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  • Biochemistry and Biotechnology  (589)
  • FLUID MECHANICS AND HEAT TRANSFER  (498)
  • 1985-1989  (1,087)
  • 1950-1954
  • 1988  (1,087)
Collection
Keywords
Publisher
Years
  • 1985-1989  (1,087)
  • 1950-1954
Year
  • 1
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    A direct interaction approximation treatment of turbulence in a compressible fluid. I - Formalism (1988)
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    Publication Date: 2011-08-19
    Description: The direct interaction approximation is used to treat turbulence in a compressible medium with constant mean gradients. The set of coupled nonlinear integrodifferential equations is derived that is satisfied by the transverse and longitudinal energy spectral functions, Q(T) and Q(L) and by the transverse and longitudinal response functions, G(T) and G(L). Finally, expressions for the average of the product of pairs of physically relevant fluctuating quantities (velocity, temperature, density) are derived in terms of Q(T) and Q(L).
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids (ISSN 0031-9171); 31; 1034-105
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  • 2
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    Generalized energy and potential enstrophy conserving finite difference schemes for the shallow water equations (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The conditions under which finite difference schemes for the shallow water equations can conserve both total energy and potential enstrophy are considered. A method of deriving such schemes using operator formalism is developed. Several such schemes are derived for the A-, B- and C-grids. The derived schemes include second-order schemes and pseudo-fourth-order schemes. The simplest B-grid pseudo-fourth-order schemes are presented.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Monthly Weather Review (ISSN 0027-0644); 116; 650-662
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  • 3
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    Renormalization-group theory for the eddy viscosity in subgrid modeling (1988)
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    Publication Date: 2011-08-19
    Description: Renormalization-group theory is applied to incompressible three-dimensional Navier-Stokes turbulence so as to eliminate unresolvable small scales. The renormalized Navier-Stokes equation now includes a triple nonlinearity with the eddy viscosity exhibiting a mild cusp behavior, in qualitative agreement with the test-field model results of Kraichnan. For the cusp behavior to arise, not only is the triple nonlinearity necessary but the effects of pressure must be incorporated in the triple term. The renormalized eddy viscosity will not exhibit a cusp behavior if it is assumed that a spectral gap exists between the large and small scales.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physical Review A - General Physics, 3rd Series (ISSN 0556-2791); 37; 2590-259
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  • 4
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    The centring dynamics of a thin liquid shell in capillary oscillations (1988)
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    Publication Date: 2011-08-19
    Description: The physical mechanism governing the centring of a hollow liquid shell in capillary oscillations, which has been observed in experiments, is investigated theoretically. First, the shell is assumed to be inviscid and to have a thickness that is much less than its spherical radius. A system of one-dimensional nonlinear equations of motion is derived using a thin-sheet model. From a numerical study the nonlinear effects of the wave are found to cause the core to oscillate slowly relative to the shell while the centre of mass of the whole system remains stationary. The effects of small viscosity are then considered in an approximation. Finally the strength of the centring mechanism is compared with that of the decentring effect due to buoyancy. The findings are consistent with the limited experimental information available.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 188; 411-435
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  • 5
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    Developing fluid flow in a curved duct of square cross-section and its fully developed dual solutions (1988)
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    Publication Date: 2011-08-19
    Description: Developing fluid flow in a curved duct of square cross-section is studied numerically by a factored ADI finite-difference method on a staggered grid. A central-difference scheme with primitive variables is used inside the computational domain to reduce numerical diffusion. Two Reynolds numbers, 574 and 790, based upon a bulk velocity and hydraulic diameter are chosen for curvature ratios of 1/6.45 and 1/2.3, respectively. It is found that the secondary flow is far more complicated than expected, with the appearance of at least two pairs of vortices. Main-flow separation is also observed for the higher curvature ratio. Furthermore, it is observed that the flow develops into two quite different states downstream, depending upon the inlet conditions. Solutions of the fully developed Navier-Stokes equations is shown to be not unique beyond a certain critical Reynolds number. Developing flow seems to evolve into the fully developed state along a particular branch into which the fully developed solution bifurcates.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 188; 337-361
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  • 6
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    Multiphase flow in porous media (1988)
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    Publication Date: 2011-08-19
    Description: A development history and current status evaluation are presented for the theory of permeability and percolation. The microscale phenomena treated in this field have proven difficult to analyze due both to their tortuous geometry and the influence of capilarity. Capilary effects may be not only important but predominant, and are differentiated into those at the fluid-fluid interface, and those involving the existence of a contact line between the solid substrate and this interface. Percolation theory has been borrowed from physics and adapted to the two-phase engineering context.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 7
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    Condensation heat transfer in a microgravity environment (1988)
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 2; 82-84
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  • 8
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    Flow-induced morphological instabilities - The rotating disc (1988)
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    Publication Date: 2011-08-19
    Description: The morphological stability of a rotating and solidifying disk is investigated under the assumption that delta, the thickness of the viscous boundary layer, is much larger than delta(c), the thickness of the solute boundary layer. It is found that axisymmetric disturbances with wavelengths comparable to delta respond to nonparallel flow effects and have stability characteristics quite different from disturbances in a parallel flow. These long waves are unstable because of the nonparallel flow and would decay without it. This analysis thus identifies a new mechanism of morphological change induced by flow.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Crystal Growth (ISSN 0022-0248); 87; 4, Ma; 385-396
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  • 9
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    On the receptivity of free shear layers to two-dimensional external excitation (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In this paper, the receptivity of a typical free shear layer to pulse-type and periodic excitation is studied. This is done by solving the initial-value problem completely and studing its long-time behavior. This leads to a wave packet for the pulse. By the superposition of many wave packets, a spatial instability mode when the flow is convectively unstable is generated. This establishes a general and simple relationship between the receptivities for pulse-type and sinusoidal excitations. It is found that a shear layer is very receptive to high-frequency disturbances that are generated near the centerline of the layer.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 187; 155-177
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  • 10
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    Direct simulation of a turbulent boundary layer up to R sub theta = 1410 (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The turbulent boundary layer on a flat plate, with zero pressure gradient, is simulated numerically at four stations between R sub theta = 225 and R sub theta = 1410. The three-dimensional time-dependent Navier-Stokes equations are solved using a spectral method with up to about 10 to the 7th grid points. Periodic spanwise and streamwise conditions are applied, and a multiple-scale procedure is applied to approximate the slow streamwise growth of the boundary layer. The flow is studied, primarily, from a statistical point of view. The solutions are compared with experimental results. The scaling of the mean and turbulent quantities with Reynolds number is compared with accepted laws, and the significant deviations are documented. The turbulence at the highest Reynolds number is studied in detail. The spectra are compared with various theoretical models. Reynolds-stress budget data are provided for turbulence-model testing.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 187; 61-98
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  • 11
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    A direct interaction approximation treatment of high Rayleigh number convective turbulence and comparison with experiment (1988)
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    Publication Date: 2011-08-19
    Description: A method is proposed for treating steady-state, thermally driven convection using the full direct interaction approximation to treat the nonlinear energy transfer and a prescribed instability function to model the eenrgy input. The instability function used is the growth rate of the mechanism generating the turbulence. This methodology can be easily generalized and applied to other driving mechanisms. The 1/3 power law form of the N vs. R relation for water is duplicated here and the coefficient is computed, using a two-point closure, to be less than about 0.08.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids (ISSN 0031-9171); 31; 256-262
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  • 12
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    Velocity spectra in the irrotational flow outside a turbulent shear layer (1988)
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    Publication Date: 2011-08-19
    Description: The relationship between the spectra of the three normal stresses near a turbulent shear layer is derived from the constraint of irrotationality. The relationship implies that the common practice of determining time scales of the turbulence from spectra in the near field is not valid. This implication is reinforced by a discussion of the scaling of irrotational spectra that follows from the formulation of Phillips (1975).
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids (ISSN 0031-9171); 31; 1807
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  • 13
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    Ejection mechanisms in the sublayer of a turbulent channel (1988)
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    Publication Date: 2011-08-19
    Description: The structure of the vorticity field in the viscous wall layer of a turbulent channel is studied by examining the results of a fully resolved direct numerical simulation. It is shown that this region is dominated by intense three-dimensional shear layers in which the dominant vorticity component is spanwise. The advection and reproduction processes of these structures are examined and shown to be consistent with the classical generation mechanism for two-dimensional Tollmien-Schlichting waves. This process is fundamentally different from the usually accepted mechanism involving hairpin vortices.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids (ISSN 0031-9171); 31; 1311-131
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  • 14
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    A finite element computation of turbulent boundary layer flows with an algebraic stress turbulence model (1988)
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    Publication Date: 2011-08-19
    Description: An algebraic stress turbulence model and a computational procedure for turbulent boundary layer flows which is based on the semidiscrete Galerkin FEM are discussed. In the algebraic stress turbulence model, the eddy viscosity expression is obtained from the Reynolds stress turbulence model, and the turbulent kinetic energy dissipation rate equation is improved by including a production range time scale. Good agreement with experimental data is found for the examples of a fully developed channel flow, a fully developed pipe flow, a flat plate boundary layer flow, a plane jet exhausting into a moving stream, a circular jet exhausting into a moving stream, and a wall jet flow.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Computer Methods in Applied Mechanics and Engineering (ISSN 0045-7825); 66; 45-63
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  • 15
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    Free-streamline analysis of deformation and dislodging by wind force of drops on a surface (1988)
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    Publication Date: 2011-08-19
    Description: Free-streamline theory is used to analyze the deformation and dislodging by wind pressure of drops of liquid adhered by surface tension to a solid surface. The critical Weber number for droplets to be dislodged is determined as a function of advancing and receding contact angle. Graphical results for drop shape are in good agreement with observation.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids (ISSN 0031-9171); 31; 43-48
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  • 16
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    Considerations on the moving contact-line singularity, with application to frictional drag on a slender drop (1988)
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    Publication Date: 2011-08-19
    Description: It has previously been shown that the no-slip boundary conditions leads to a singularity at a moving contact line and that this presumes some form of slip. Present considerations on the energetics of slip due to shear stress lead to a yield stress boundary condition. A model for the distortion of the liquid state near solid boundaries gives a physical basis for this boundary condition. The yield stress condition is illustrated by an analysis of a slender drop rolling down an incline. That analysis provides a formula for the frictional drag resisting the drop movement. With the present boundary condition, the length of the slip region becomes a property of the fluid flow.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 197; 157-169
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  • 17
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    Lower-upper Symmetric-Gauss-Seidel method for the Euler and Navier-Stokes equations (1988)
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 26; 1025
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  • 18
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    Numerical study of the interactions between droplets at intermediate Reynolds numbers (1988)
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Propulsion and Power (ISSN 0748-4658); 4; 481-489
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  • 19
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    Unsteady solution of incompressible Navier-Stokes equations (1988)
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    Publication Date: 2011-08-19
    Description: The numerical scheme used by the present time-accurate FEM numerical method for incompressible Navier-Stokes equations, using primitive variables as the unknowns, is a Crank-Nicholson implicit treatment of all equation terms with central differencing for space derivatives. The introduction of a continuous auxilliary system in pseudo-time, with artificial compressibility, yields the incompressible solution at the advanced time level; time-accurate solutions are thereby obtained for two-dimensional fluid flows in a square cavity, in the cases of both an impulsively starting lid and an oscillating lid.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 79; 113-134
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  • 20
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    Measurements of the free-stream fluctuations above a turbulent boundary layer (1988)
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    Publication Date: 2011-08-19
    Description: The paper describes an investigation of the velocity fluctuations in the free stream above an incompressible turbulent boundary layer developing at constant pressure. Measurements were performed in a wind tunnel with an rms level of axial velocity fluctuations of about 0.2 percent. The possibility of assessing the contributions to the rms level of the velocity fluctuations without using the high-pass filtering technique is demonstrated.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids (ISSN 0031-9171); 31; 2834-284
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  • 21
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    Model consistency in large eddy simulation of turbulent channel flows (1988)
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    Publication Date: 2011-08-19
    Description: Combinations of filters and subgrid scale stress models for large eddy simulation of the Navier-Stokes equations are examined by a priori tests and numerical simulations. The structure of the subgrid scales is found to depend strongly on the type of filter used, and consistency between model and filter is essential to ensure accurate results. The implementation of consistent combinations of filter and model gives more accurate turbulence statistics than those obtained in previous investigations in which the models were chosen independently from the filter. Results and limitations of the a priori test are discussed. The effect of grid refinement is also examined.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids (ISSN 0031-9171); 31; 1884-189
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  • 22
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    Structure of rough-wall turbulent boundary layers (1988)
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    Publication Date: 2011-08-19
    Description: Recent experiments have shown that, in rough-wall turbulent boundary layers, drag varies systematically with the spanwise aspect ratio lambda(z) (span/height) of roughness elements. In this paper, the effect of lambda(z) on turbulence structure has been examined. Based on lambda(z), the roughness in a transversely grooved surface with lambda(z) much greater than 1 is the opposite extreme of model plant canopies with lambda(z) much less than 1, studied in wind tunnels, whereas sandgrain is an intermediate type. Second-, third-, and fourth-order turbulence moments have been measured in turbulent boundary layers over transversely grooved and smooth surfaces and compared with available turbulence structure measurements over other types of surfaces. The near-wall turbulence structure is found to vary with lambda(z). The instantaneous motions involved in the flux of shear stress near the wall in smooth and transversely grooved surfaces are opposite in sign to those in three-dimensional roughness. The former is explained in terms of hairpin vortices alone, while the latter group is modeled to have an additional vortex (the so-called necklace vortex which straddles a three-dimensional roughness element near its base).
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids (ISSN 0031-9171); 31; 1877-188
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  • 23
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    Stability of swirling gas flows (1988)
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    Publication Date: 2011-08-19
    Description: The stability of inviscid swirling gas flows to small nonaxisymmetric perturbations is considered. For small Brunt-Vaisala frequencies, the problem reduces to the classical Sturm-Liouville form and the oscillation theorem can be applied. The resulting necessary and sufficient stability condition is compared to various criteria in the literature and a limited numerical study of isothermal rigidly rotating Poiseuille flow. For given azimuthal and axial wavenumbers, it is found numerically that the higher inertial modes become unstable for successively lower Rossby numbers and that this sequence of critical values approaches the theoretical value from above.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids (ISSN 0031-9171); 31; 1872-187
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  • 24
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    Weak solutions of the three-dimensional vorticity equation with vortex singularities (1988)
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    Publication Date: 2011-08-19
    Description: The extension of the concept of vortex singularities, developed by Saffman and Meiron (1986) for the case of two-dimensional point vortices in an incompressible vortical flow, to the three-dimensional case of vortex sticks (vortons) is investigated analytically. The derivation of the governing equations is explained, and it is demonstrated that the formulation obtained conserves total vorticity and is a weak solution of the vorticity equation, making it an appropriate means for representing three-dimensional vortical flows with limited numbers of vortex singularities.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids (ISSN 0031-9171); 31; 1838
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  • 25
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    Rain simulation studies for high-intensity acoustic nose cavities (1988)
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    Publication Date: 2011-08-19
    Description: Unarmed plastic projectiles can be equipped with small axisymmetric cavities for the generation of intense tones that are useful in training maneuvers. Attention is presently given to the simulation of rainfall in an airstream and the effect of rain droplet impingement on the nose of projectiles, and especially to any penetration or accumulation of water at the base of the cavity that might increase the fundamental cavity frequency and/or reduce the intensity of sound production during rain conditions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Aircraft (ISSN 0021-8669); 25; 281-283
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  • 26
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    Equilibrium shapes of rotating spheroids and drop shape oscillations (1988)
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    Publication Date: 2011-08-19
    Description: Recent work on the equilibrium shapes of a rotating spheroid and drop shape oscillations is reviewed. The related theoretical aspects of the equilibrium shapes of a rotating drop, the stability, shape oscillations, gravitational forces, and drop fission are examined. Experimental findings on figures of a rotating drop in an immiscible system, drop oscillations in an immiscible system, oscillations of a rotating drop, compound drop oscillations, and drop dynamics in space are addressed.
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  • 27
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    Oxygen plasma effects on several liquid droplet radiator fluids (1988)
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 25; 99-101
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  • 28
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    Solutions of one-dimensional steady nozzle flow revisited (1988)
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    Publication Date: 2011-08-19
    Description: A formulation is presented by which any iteration process for obtaining the entropy increase in the flow of a one-dimensional steady nozzle is eliminated, and the simple solution of a quadratic equation is obtained. The proper parameters are then explicitly seen in the equation, and their effects on the solution are easily determined. Since only one root of the equation is physically admissible, entropy production, and therefore the shock wave, are uniquely determined by this set of parameters.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 26; 625-628
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  • 29
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    Karhunen-Loeve expansion of Burgers' model of turbulence (1988)
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    Publication Date: 2011-08-19
    Description: The properties of the Karhunen-Loeve expansion of a strongly inhomogeneous random process are examined with emphasis on applications to turbulent flow fields. The ability of the KL expansion to represent functions that have both slow and rapid variations in a relatively small number of expansion terms is tested on a one-dimensional model based on the forced Burgers' equation. The rate of the convergence of the expansion is evaluated, and its dependence on the Reynolds number is determined. It is shown that the KL eigenfunctions possess wall boundary layers attached to outer structures that are independent of the Reynolds number (at high Reynolds numbers). It is also shown that the spectrum of eigenvalues is broad at large Reynolds numbers, requiring many terms to represent higher-order derivatives of the function.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids (ISSN 0031-9171); 31; 2573-258
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  • 30
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    On the nonlinear interaction of Goertler vortices and Tollmien-Schlichting waves in curved channel flows at finite Reynolds numbers (1988)
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    Publication Date: 2011-08-19
    Description: The flow in a two-dimensional curved channel driven by an azimuthal pressure gradient can become linearly unstable due to axisymmetric perturbations and/or nonaxisymmetric perturbations depending on the curvature of the channel and the Reynolds number. For a particular small value of curvature, the critical neighborhood of this curvature value and critical Reynolds number, nonlinear interactions occur between these perturbations. The Stuart-Watson approach is used to derive two coupled Landau equations for the amplitudes of these perturbations. The stability of the various possible states of these perturbations is shown through bifurcation diagrams. Emphasis is given to those cases which have relevance to external flows.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 193; 569-595
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  • 31
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    Experimental and theoretical effects of nitrogen gas flow rate on liquid-jet atomization (1988)
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Propulsion and Power (ISSN 0748-4658); 4; 406-411
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  • 32
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    Experimental study of thermocapillary flows in a thin liquid layer with heat fluxes imposed on the free surface (1988)
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    Publication Date: 2011-08-19
    Description: To study thermocapillary flows in a two-dimensional thin liquid layer with heat fluxes imposed on the free surface experimentally, a long tray configuration was employed to simulate the infinite layer. The surface temperature distribution due to thermocapillary convection for different flow regimes was measured and compared with theorectical predictions. A short tray configuration was also employed to study the end wall effects (insulating or conducting). The results show that, for a strong convection flow with an insulating wall as the boundary, the surface temperature distribution became quite uniform. Consequently, the thermocapillary driving force was greatly reduced. On the other hand, a strong fluid motion always existed adjacent to the conducting wall because of the large surface temperature gradient near the wall.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Metallurgical Transactions A - Physical Metallurgy and Materials Science (ISSN 0360-2133); 19A; 1895-189
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  • 33
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    Transfinite element methodology for nonlinear/linear transient thermal modelling/analysis - Progress and recent advances (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The 'transfinite element method' (TFEM) proposed by Tamma and Railkar (1987 and 1988) for the analysis of linear and nonlinear heat-transfer problems is described and demonstrated. The TFEM combines classical Galerkin and transform approaches with state-of-the-art FEMs to obtain a flexible hybrid modeling scheme. The fundamental principles of the TFEM and the derivation of the governing equations are reviewed, and numerical results for sample problems are presented in extensive graphs and briefly characterized. Problems analyzed include a square plate with a hole, a rectangular plate with natural and essential boundary conditions and varying thermal conductivity, the Space Shuttle thermal protection system, a bimaterial plate subjected to step temperature variations, and solidification in a semiinfinite liquid slab.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal for Numerical Methods in Engineering (ISSN 0029-5981); 25; 475-494
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    Determination of convective diffusion heat/mass transfer rates to burner rig test targets comparable in size to cross-stream jet diameter (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: ASME, Transactions, Journal of Heat Transfer (ISSN 0022-1481); 110; 449-455
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    Reynolds-stress and dissipation-rate budgets in a turbulent channel flow (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The budgets for the Reynolds stresses and for the dissipation rate of the turbulence kinetic energy are computed using direct simulation data of a turbulent channel flow. The budget data reveal that all the terms in the budget become important close to the wall. For inhomogeneous pressure boundary conditions, the pressure-strain term is split into a return term, a rapid term, and a Stokes term. The Stokes term is important close to the wall. The rapid and return terms play different roles depending on the component of the term. A split of the velocity pressure-gradient term into a redistributive term and a diffusion term is proposed, which should be simpler to model. The budget data is used to test existing closure models for the pressure-strain term, the dissipation rate, and the transport rate. In general, further work is needed to improve the models.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 194; 15-44
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    Transient radiative cooling of an absorbing and scattering cylinder - A separable solution (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A cylindrical region filled with absorbing-emitting material is cooled by radiation to surroundings at a much lower temperature. A solution is found showing that, for each set of parameters, the transient radial temperature distribution reaches a fixed shape, although the temperatures are decreasing with time. This 'fully developed' transient region is characterized by having a constant emittance based on instantaneous values of the cylinder heat loss and mean temperature. This emittance depends only on the optical radius of the cylinder and the scattering albedo. The emittance is lower than that for a cylinder at uniform temperature. This arises from the larger local cooling and, hence, reduced temperatures of the outer layers of the cylinder. An examination of this transient emittance provides the ranges of parameters within which the simplification can be made that the cylinder has uniform radial temperature distribution throughout the cooling process.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 2; 110-117
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    Nonlinear vortex trail dynamics (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The nonlinear evolution of periodic disturbances on vortex trails is considered. In addition to following small initial perturbations, large amplitude initial disturbances of the vortex trails are also studied. It is shown that the equations support a rich variety of essentially nonlinear solutions including unbounded and quasisteady ones. These solutions are found to correspond to various modes of vortex clustering in the physical plane. At the close of the paper, comparisons of these results with recent numerical and experimental findings on the wakes behind stationary cylinders, and also transversely oscillating bluff objects, are made.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids (ISSN 0031-9171); 31; 991-998
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    Computation of the velocity field of an excited shear layer (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An infinitely thin shear layer emanating from a semi-infinite flat plate subjected to acoustic excitation is considered. The flow field outside the excited shear layer is computed employing a source distribution approach. Results are given for the region of the velocity field that cannot easily be obtained by analytical approximations.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Communications in Applied Numerical Methods (ISSN 0748-8025); 4; 85-89
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    Overlapping grids for flow field calculations (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Many problems in computational fluid dynamics (CFD) involve the calculation of flow fields within or around complex geometric configurations. The flow solution is computed on a computational grid. The construction of the grid is one of the major difficulties in the application of CFD to the analysis of flow about actual aircraft configurations. Due to geometric complexity, the grid has to be constructed in simple subregions and then all of these subgrids have to be pieced together to form a complete grid for the entire flow field. The entire grid, which is called a composite grid because it is formed from many parts, may have common regions. In either case, the computation of the flow field, using any numerical algorithm, will require the transfer of information between individual subgrids. The transfer of information is more difficult with overlapping grids. Algorithms have been developed and tested for automating the transfer of information between two overlapping grids.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Hampton Inst., NASA/American Society for Engineering Educ; Hampton Inst., NASA(
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    Modeling of transitional flows (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: An effort directed at developing improved transitional models was initiated. The focus of this work was concentrated on the critical assessment of a popular existing transitional model developed by McDonald and Fish in 1972. The objective of this effort was to identify the shortcomings of the McDonald-Fish model and to use the insights gained to suggest modifications or alterations of the basic model. In order to evaluate the transitional model, a compressible boundary layer code was required. Accordingly, a two-dimensional compressible boundary layer code was developed. The program was based on a three-point fully implicit finite difference algorithm where the equations were solved in an uncoupled manner with second order extrapolation used to evaluate the non-linear coefficients. Iteration was offered as an option if the extrapolation error could not be tolerated. The differencing scheme was arranged to be second order in both spatial directions on an arbitrarily stretched mesh. A variety of boundary condition options were implemented including specification of an external pressure gradient, specification of a wall temperature distribution, and specification of an external temperature distribution. Overall the results of the initial phase of this work indicate that the McDonald-Fish model does a poor job at predicting the details of the turbulent flow structure during the transition region.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Hampton Inst., NASA/American Society for Engineering Educ; Hampton Inst., NASA(
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    Energy transfer in isotropic turbulence at low Reynolds numbers (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Detailed measurements were made of energy transfer among the scales of motion in incompressible turbulent fields at low Reynolds numbers generated by direct numerical simulation. It was observed that although the transfer resulted from triad interactions that were non-local in k space, the energy always transferred locally. The results are consistent with the notion of non-uniform advection of small weak eddies by larger and stronger ones, similar to transfer processes in the far dissipation range at high Reynolds numbers.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Stanford Univ., Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program; p 169-177
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  • 42
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    Multifractal spectra in homogeneous shear flow (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Employing numerical simulations of 3-D homogeneous shear flow, the associated multifractal spectra of the energy dissipation, scalar dissipation and vorticity fields were calculated. The results for (128) cubed simulations of this flow, and those obtained in recent experiments that analyzed 1- and 2-D intersections of atmospheric and laboratory flows, are in some agreement. A two-scale Cantor set model of the energy cascade process which describes the experimental results from 1-D intersections quite well, describes the 3-D results only marginally.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program; p 157-167
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  • 43
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    Pressure-strain-rate events in homogeneous turbulent shear flow (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A detailed study of the intercomponent energy transfer processes by the pressure-strain-rate in homogeneous turbulent shear flow is presented. Probability density functions (pdf's) and contour plots of the rapid and slow pressure-strain-rate show that the energy transfer processes are extremely peaky, with high-magnitude events dominating low-magnitude fluctuations, as reflected by very high flatness factors of the pressure-strain-rate. A concept of the energy transfer class was applied to investigate details of the direction as well as magnitude of the energy transfer processes. In incompressible flow, six disjoint energy transfer classes exist. Examination of contours in instantaneous fields, pdf's and weighted pdf's of the pressure-strain-rate indicates that in the low magnitude regions all six classes play an important role, but in the high magnitude regions four classes of transfer processes, dominate. The contribution to the average slow pressure-strain-rate from the high magnitude fluctuations is only 50 percent or less. The relative significance of high and low magnitude transfer events is discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program; p 143-156
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    Scalar entrainment in the mixing layer (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: New definitions of entrainment and mixing based on the passive scalar field in the plane mixing layer are proposed. The definitions distinguish clearly between three fluid states: (1) unmixed fluid, (2) fluid engulfed in the mixing layer, trapped between two scalar contours, and (3) mixed fluid. The difference betwen (2) and (3) is the amount of fluid which has been engulfed during the pairing process, but has not yet mixed. Trends are identified from direct numerical simulations and extensions to high Reynolds number mixing layers are made in terms of the Broadwell-Breidenthal mixing model. In the limit of high Peclet number (Pe = ReSc) it is speculated that engulfed fluid rises in steps associated with pairings, introducing unmixed fluid into the large scale structures, where it is eventually mixed at the Kolmogorov scale. From this viewpoint, pairing is a prerequisite for mixing in the turbulent plane mixing layer.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program; p 69-76
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    Phase decorrelation, streamwise vortices and acoustic radiation in mixing layers (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Several direct numerical simulations were performed and analyzed to study various aspects of the early development of mixing layers. Included are the phase jitter of the large-scale eddies, which was studied using a 2-D spatially-evolving mixing layer simulation; the response of a time developing mixing layer to various spanwise disturbances; and the sound radiation from a 2-D compressible time developing mixing layer.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program; p 29-39
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    A numerical study of bifurcations in a barotropic shear flow (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: In the last few years, more and more evidence has emerged suggesting that transition to turbulence may be viewed as a succession of bifurcations to deterministic chaos. Most experimental and numerical observations have been restricted to Rayleigh-Benard convection and Taylor-Couette flow between concentric cylinders. An attempt is made to accurately describe the bifurcation sequence leading to chaos in a 2-D temporal free shear layer on the beta-plane. The beta-plane is a locally Cartesian reduction of the equations describing the dynamicss of a shallow layer of fluid on a rotating spherical planet. It is a valid model for large scale flows of interest in meteorology and oceanography.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program; p 41-47
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    Analysis of homogeneous turbulent reacting flows (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Full turbulence simulations at low Reynolds numbers were made for the single-step, irreversible, bimolecular reaction between non-premixed reactants in isochoric, decaying homogeneous turbulence. Various initial conditions for the scalar field were used in the simulations to control the initial scalar dissipation length scale, and simulations were also made for temperature-dependent reaction rates and for non-stoichiometric and unequal diffusivity conditions. Joint probability density functions (pdf's), conditional pdf's, and various statistical quantities appearing in the moment equations were computed. Preliminary analysis of the results indicates that compressive strain-rate correlates better than other dynamical quantities with local reaction rate, and the locations of peak reaction rates seem to be insensitive to the scalar field initial conditions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program; p 243-255
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    Eddies, streams, and convergence zones in turbulent flows (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Recent studies of turbulent shear flows have shown that many of their important kinematical and dynamical properties can be more clearly understood by describing the flows in terms of individual events or streamline patterns. These events or flow regions are studied because they are associated with relatively large contributions to certain average properties of the flow, for example kinetic energy, Reynolds stress, or to particular processes in the flow, such as mixing and chemical reactions, which may be concentrated at locations where streamlines converge for fast chemical reactions (referred to as convergence or C regions), or in recirculating eddying regions for slow chemical reactions. The aim of this project was to use the numerical simulations to develop suitable criteria for defining these eddying or vortical zones. The C and streaming (S) zones were defined in order to define the whole flow field. It is concluded that homogeneous and sheared turbulent flow fields are made up of characteristic flow zones: eddy, C, and S zones. A set of objective criteria were found which describe regions in which the streamlines circulate, converge or diverge, and form high streams of high velocity flow.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program; p 193-208
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    Subharmonic resonance in a mixing layer (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The subharmonic resonance phenomenon in a spatially evolving mixing layer is studied using direct simulations of the 2-D Navier-Stokes equations. The computational domain extends to + or - infinity in the cross-stream direction with U(1) = 1.25 and U(2) = 0.25 imposed at + infinity and - infinity respectively. The domain is finite in the streamwise direction with inflow and outflow boundary conditions imposed at x/delta sub omega = 0 and 100, respectively. A hyperbolic-tangent mean velocity profile is assumed at the inlet and the Reynolds number based on the inlet vorticity thickness and velocity difference is Re = 600. It is observed that the phase angle between the fundamental and its subharmonic plays a key role in the spatial development of these modes. Contour plots of vorticity show that varying the phase will have a dramatic effect on the dynamics of the vortices. Pairing or shredding is observed depending on the phase. Fourier decomposition of the time traces show that the fundamental grows, saturates and decays with the downstream distance. The subharmonic has a similar behavior. However, the level at which the modes will saturate is affected by the phase. At 0 deg phase, it was found that as the fundamental saturates, the growth rate of the subharmonic is enhanced. At 90 deg phase, it was found that as the fundamental saturates, the growth rate of the subharmonic is inhibited. In the later case, the growth rate of the subharmonic recovers after saturation of the fundamental. These results are in qualitative agreement with experimental data.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Stanford Univ., Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program; p 57-68
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    Inflow/outflow boundary conditions and global dynamics of spatial mixing layers (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The numerical simulation of incompressible spatially-developing shear flows poses a special challenge to computational fluid dynamicists. The Navier-Stokes equations are elliptic and boundary equations need to be specified at the inflow and outflow boundaries in order to compute the fluid properties within the region of interest. It is, however, difficult to choose inflow and outflow conditions corresponding to a given experimental situation. Furthermore the effects that changes in the boundary conditions or in the size of the computational domain may induce on the global dynamics of the flow are presently unknown. These issues are examined in light of recent developments in hydrodynamic stability theory. The particular flow considered is the spatial mixing layer but it was expected that similar phenomena were bound to occur in other cases such as channel flow, the boundary layer, etc. A short summary of local/global and absolute/convective instability concepts is given. The results of numerical simulations are presented which strongly suggest that global resonances may be triggered in domains of finite streamwise extent although the evolution of the perturbation vorticity field is everywhere locally convective. A relationship between finite domains and pressure sources which might help in devising a scheme to eliminate these difficulties is discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Stanford Univ., Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program; p 19-27
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    Chaos in a spatially-developing plane mixing layer (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: A spatially-developing plane mixing layer was analyzed for chaotic behavior. A direct numerical simulation of the Navier-Stokes equations in a 2-D domain infinite in y and having inflow-outflow boundary conditions in x was used for data. Spectra, correlation dimension and the largest Lyapunov exponent were computed as functions of downstream distance x. When forced at a single (fundamental) frequency with maximum amplitude, the flow is periodic at the inflow but becomes aperiodic with increasing x. The aperiodic behavior is caused by the presence of a noisy subharmonic caused by the feedback between the necessarily nonphysical inflow and outflow boundary conditions. In order to overshadow this noise the flow was also studied with the same fundamental forcing and added random forcing of amplitude upsilon prime sub R/delta U = 0.01 at the inlet. Results were qualitatively the same in both cases: for small x, spectral peaks were sharp and dimension was nearly 1, but as x increased a narrowband spectral peak grew, spectra decayed exponentially at high frequencies and dimension increased to greater than 3. Based on these results, the flow appears to exhibit deterministic chaos. However, at no location was the largest Lyapunov exponent found to be significantly greater than zero.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Stanford Univ., Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program; p 3-18
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    Theoretical model for VITA-educed coherent structures in the wall region of a turbulent boundary layer (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Experiments on wall-bounded shear flows (channel flows and boundary layers) have indicated that the turbulence in the region close to the wall exhibits a characteristic intermittently formed pattern of coherent structures. For a quantitative study of coherent structures it is necessary to make use of conditional sampling. One particularly successful sampling technique is the Variable Integration Time Averaging technique (VITA) first explored by Blackwelder and Kaplan (1976). In this, an event is assumed to occur when the short time variance exceeds a certain threshold multiple of the mean square signal. The analysis presented removes some assumptions in the earlier models in that the effects of pressure and viscosity are taken into account in an approximation based on the assumption that the near-wall structures are highly elongated in the streamwise direction. The appropriateness of this is suggested by the observations but is also self consistent with the results of the model which show that the streamwise dimension of the structure grows with time, so that the approximation should improve with the age of the structure.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Stanford Univ., Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program; p 209-220
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    Optical propagation through a homogeneous turbulent shear flow (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Effects of organized turbulent structures on the propagation of an optical beam in a homogeneous shear flow were studied. A passive-scalar field in a computed turbulent shear flow is used to represent index-of-refraction fluctuations, and phase errors induced in a coherent optical beam by turbulent fluctuations are computed. The organized vortical structures produce a scalar distribution with elongated regions of intense fluctuations which have an inclination with respect to the mean flow similar to that of the characteristic hairpin eddies. It is found that r.m.s. phase error is minimized by propagating approximately normal to the inclined vortical structures. Two-point correlations of vorticity and scalar fluctuation suggest that the regions of intense scalar fluctuation are produced primarily by the hairpin eddies.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program; p 311-320
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    The structure of sheared turbulence near a plane boundary (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: An analysis is presented of how a plane boundary affects the structure of turbulence in a sheared free stream. A uniform-shear boundary layer (USBL) is formulated with slip velocity condition at the surface, and inhomogeneous rapid distortion theory is applied. The effects of blocking by the surface on the turbulence structure in USBL is compared with those in the shear-free boundary layer (SFBL). Shear produces highly anisotropic eddies elongated in the flow direction. The vertical velocity variance is reduced with shear at all heights, roughly in proportion to the reduction in the homogeneous value, but the shape of the profile remains unchanged only near the surface. The streamwise integral scales increase with shear, indicating elongation of the streamwise extent of eddies.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program; p 221-241
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    Turbulence characteristics inside a turbulent spot in plane Poiseuille flow (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: In wall-bounded shear flows the transition to turbulence through localized disturbances goes through a pattern starting with a development of shear layers. The localized normal velocity fluctuations induce normal vorticity through the lift-up effect. These shear layers become unstable to secondary disturbances, and if the amplitudes of the disturbances are large enough, a turbulent spot develops. Investigations of the spot in boundary layers has shown that the turbulent part of the spot is very similar to a fully developed boundary layer. Wygnanski et al. (1976) showed that the mean profile at the center-symmetry plane has a logarithmic region and Johansson et al. (1987) showed that both the higher-order statistics and flow structures in the spot were the same as in the corresponding fully developed flow. In what respects the turbulence inside the Poiseuille spot is similar to fully developed turbulent channel flow is studied. The numerically simulated spot is used, where the characteristics inside the spot are compared to those of the wave packet in the wingtip area. A recent experimental investigation of the velocity field associated with the Poiseuille spot by Klingmann et al. is used for comparison.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Stanford Univ., Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program; p 179-192
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    Turbulence production near walls: The role of flow structures with spanwise asymmetry (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Space-time evolution of near wall flow structures is described by conditional sampling methods, in which conditional averages are formed at various stages of development of shear layer structures. The development of spanwise asymmetry of the structures was found to be important in the creation of the structures and for the process of turbulence production.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Stanford Univ., Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program; p 131-141
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    Sensitivity of mixing layers to three-dimensional forcing (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: It is well known that turbulent mixing layers are dominated by large scale, fairly coherent structures, and that these structures are related to the stability characteristics of the flow. These facts have led researchers to attempt controlling such flows by selectively forcing certain unstable modes, which can in addition have the effect of suppressing other modes. Much of the work on controlling the mixing layer has relied on forcing 2-D instabilities. The results of forcing 3-D instabilities are addressed. The objectives of the work are twofold: to understand how a mixing layer responds to 3-D perturbations, and to test the validity of an amplitude expansion in predicting the mixing layer development. The amplitude expansion could be very useful in understanding and predicting the 3-D response of the flow to a variety of initial conditions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Stanford Univ., Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program; p 91-116
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    Use of passive scalar tagging for the study of coherent structures in the plane mixing layer (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Data obtained from the numerical simulation of a 2-D mixing layer were used to study the feasibility of using the instantaneous concentration of a passive scalar for detecting the typical coherent structures in the flow. The study showed that this technique works quite satisfactorily and yields results similar to those that can be obtained by using the instantaneous vorticity for structure detection. Using the coherent events educed by the scalar conditioning technique, the contribution of the coherent events to the total turbulent momentum and scalar transport was estimated. It is found that the contribution from the typical coherent events is of the same order as that of the time-mean value. However, the individual contributions become very large during the pairing of these structures. The increase is particularly spectacular in the case of the Reynolds shear stress.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program; p 77-89
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    Dynamics of coherent structures in a plane mixing layer (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: An incompressible, time developing 3-D mixing layer with idealized initial conditions was simulated numerically. Consistent with the suggestions from experimental measurements, the braid region between the dominant spanwise vortices or rolls develops longitudinal vortices or ribs, which are aligned upstream and downstream of a roll and produce spanwise distortion of the rolls. The process by which this distortion occurs is explained by studying a variety of quantities of dynamic importance (e.g., production of enstrophy, vortex stretching). Other quantities of interest (dissipation, helicity density) are also computed and discussed. The currently available simulation only allows the study of the early evolution (before pairing) of the mixing layer. New simulations in progress will relieve this restriction.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program; p 49-55
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    Observations of breakup processes of liquid jets using real-time X-ray radiography (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: To unravel the liquid-jet breakup process in the nondilute region, a newly developed system of real-time X-ray radiography, an advanced digital image processor, and a high-speed video camera were used. Based upon recorded X-ray images, the inner structure of a liquid jet during breakup was observed. The jet divergence angle, jet breakup length, and fraction distributions along the axial and transverse directions of the liquid jets were determined in the near-injector region. Both wall- and free-jet tests were conducted to study the effect of wall friction on the jet breakup process.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA, Marshall Space Flight Center, Mixing and Demixing Processes in Multiphase Flows with Application to Propulsion Systems; p 125-133
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    The application of single particle hydrodynamics in continuum models of multiphase flow (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: A review of the application of single particle hydrodynamics in models for the exchange of interphase momentum in continuum models of multiphase flow is presented. Considered are the equations of motion for a laminar, mechanical two phase flow. Inherent to this theory is a model for the interphase exchange of momentum due to drag between the dispersed particulate and continuous fluid phases. In addition, applications of two phase flow theory to de-mixing flows require the modeling of interphase momentum exchange due to lift forces. The applications of single particle analysis in deriving models for drag and lift are examined.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Mixing and Demixing Processes in Multiphase Flows With Application to Propulsion Systems; p 3-13
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    Migration arising from gradients in shear stress: Particle distributions in Poiseuille flow (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Experimental evidence for the existence of shear induced migration processes is reviewed and the mechanism by Leighton and Acrivos (1987b) is described in detail. The proposed mechanism is shown to lead to the existence of an additional shear induced migration in the presence of gradients in shear stress such as would be found in Poiseuille flow, and which may be used to predict the amplitude of the observed short-term viscosity increase. The concentration and velocity profiles which result from such a migration are discussed in detail and are compared to the experimental observations of Karnis, Goldsmith and Mason (1966).
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA, Marshall Space Flight Center, Mixing and Demixing Processes in Multiphase Flows with Application to Propulsion Systems; p 109-124
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    Transient heat transfer from shrinking LOX-drop (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: In order to achieve prescribed experimental conditions in wind tunnels, the nitrogen-oxygen mixture is enriched by injection of liquid oxygen (LOX) upstream of methane burners. The objective of the study is to determine the LOX drop evaporation rate, which is dominated by heat transfer from the air stream (mass transfer mechanism can be later coupled with the solution from the present work). Since the concentration of drops in the surrounding gas is quite high, the concept of infinite medium cannot be utilized. Drop evaporation, as part of system's mass balance, is an important source-term in the finite-difference 2/3-dimensional network terms of laboratory-system (Eulerian) coordinates, while individual drop behavior, including its thermal history, is analyzed in Lagrangian coordinates.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Hampton Inst., NASA/American Society for Engineering Educ; Hampton Inst., NASA(
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    An investigation of turbulence models (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The accuracy to which a turbulent boundary layer or wake can be predicted numerically depends on the validity of the turbulence closure model used. The modeling of turbulence physics is one of the most difficult problems in computational fluid dynamics (CFD). In fact, it is one of the pacing factors in the development of CFD. In general, there are three main approaches to the description of trubulence physics. First is turbulence modeling in which the Reynolds averaged Navier-Stokes equations are used and some closure approximation is made for the Reynolds stresses. A second approach to turbulence is large eddy simulation (LES) in which the computational mesh is taken to be fine enough that the large scale structure of the turbulence can be calculated directly. An empirical assumption must be made for the small scale sub-grid turbulence. The third approach is direct simulation. In this technique the Navier-Strokes equations are solved directly on a mesh which if fine enough to resolve the smallest length scale of the turbulence. The Reynolds averaged equations are not used and no closure assumption is required. These last two approaches require extensive computer resources and as such are not engineering tools. The purpose of the work was to investigate the various engineering turbulence models for accuracy and ease of programming. This involved comparison of the models with each other and with experimental data.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Hampton Inst., NASA/American Society for Engineering Educ; Hampton Inst., NASA(
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    Development of optimized, graded-permeability axial groove heat pipes (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Heat pipe performance can usually be improved by uniformly varying or grading wick permeability from end to end. A unique and cost effective method for grading the permeability of an axial groove heat pipe is described - selective chemical etching of the pipe casing. This method was developed and demonstrated on a proof-of-concept test article. The process improved the test article's performance by 50 percent. Further improvement is possible through the use of optimally etched grooves.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA, Goddard Space Flight Center, 15th Space Simulation Conference: Support the Highway to Space Through Testing; p 397-408
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    Confined turbulent fluid-particle flow modeling using multiple-realization particle trajectory schemes (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: A multiple-realization particle trajectory scheme has been developed and applied to the numerical prediction of confined turbulent fluid-particle flows. The example flows investigated include the vertical pipe upflow experimental data of Tsuji et al. and the experimental data of Leavitt for a coaxial jet flow, comprising a particle-laden central jet and a clean annular jet, into a large recirculation chamber. The results obtained from the numerical scheme agree well with the experimental data, lending confidence to the modeling approach. The multiple-realization particle trajectory turbulent flow modeling scheme is believed to be a more elegant and accurate approach to the extension of single-particle hydrodynamics to dilute multi-particle systems than the more commonly employed two-fluid modeling approach. It is also better able to incorporate additional force items such as lift, virtual mass and Bassett history terms directly into the particle equation of motion as appropriate. This makes it a suitable candidate for particle migration studies and an extension to situations involving liquid particulate phases with possible propulsion applications, such as in spray combustion, follows naturally.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Mixing and Demixing Processes in Multiphase Flows With Application to Propulsion Systems; p 55-85
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    Heat exchanger expert system logic (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The reduction is described of the operation and fault diagnostics of a Deep Space Network heat exchanger to a rule base by the application of propositional calculus to a set of logic statements. The value of this approach lies in the ease of converting the logic and subsequently implementing it on a computer as an expert system. The rule base was written in Process Intelligent Control software.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: The Telecommunications and Data Acquisition Report; p 232-244
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    Knowledge-based zonal grid generation for computational fluid dynamics (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Automation of flow field zoning in two dimensions is an important step towards reducing the difficulty of three-dimensional grid generation in computational fluid dynamics. Using a knowledge-based approach makes sense, but problems arise which are caused by aspects of zoning involving perception, lack of expert consensus, and design processes. These obstacles are overcome by means of a simple shape and configuration language, a tunable zoning archetype, and a method of assembling plans from selected, predefined subplans. A demonstration system for knowledge-based two-dimensional flow field zoning has been successfully implemented and tested on representative aerodynamic configurations. The results show that this approach can produce flow field zonings that are acceptable to experts with differing evaluation criteria.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Lyndon B. Johnson Space Center, 2nd Annual Workshop on Space Operations Automation and Robotics (SOAR 1988); p 73-80
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    The role of the turbulent Prandtl number in turbine blade heat transfer prediction (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Improvement of the prediction of external (gas-to-blade) heat transfer coefficients in gas turbine engines was undertaken. The effects of improved eddy diffusivity of heat modeling in the turbulence model was specifically investigated. A two-dimensional boundary STAN5, was selected and modified by incorporating several different turbulent Prandtl number models. Results indicated that slight effects were attributable to the modified turbulence model. Boundary layer character appeared to be much more significant.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Alabama Univ., Research Reports: 1988 NASA(ASEE Summer Faculty Fellowship Program; 20 p
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    Vortex methods for separated flows (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The numerical solution of the Euler or Navier-Stokes equations by Lagrangian vortex methods is discussed. The mathematical background is presented and includes the relationship with traditional point-vortex studies, convergence to smooth solutions of the Euler equations, and the essential differences between two and three-dimensional cases. The difficulties in extending the method to viscous or compressible flows are explained. Two-dimensional flows around bluff bodies are emphasized. Robustness of the method and the assessment of accuracy, vortex-core profiles, time-marching schemes, numerical dissipation, and efficient programming are treated. Operation counts for unbounded and periodic flows are given, and two algorithms designed to speed up the calculations are described.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: VKI, Computational Fluid Dynamics, Volume 1; 64 p
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    Convergence speeding up in the calculation of the viscous flow about an airfoil (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: A finite volume method to solve the three dimensional Navier-Stokes equations was developed. It is based on a cell-vertex scheme with central differences and explicit Runge-Kutta time steps. A good convergence for a stationary solution was obtained by the use of local time steps, implicit smoothing of the residues, a multigrid algorithm, and a carefully controlled artificial dissipative term. The method is illustrated by results for transonic profiles and airfoils. The method allows a routine solution of the Navier-Stokes equations.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: DGLR, Flows with Separation; p 301-312
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    Ammonia transfer across rotating joints in space (1988)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Thermal control of future large space facilities, such as the space station, will require the transfer of anhydrous ammonia across rotating joints with near zero leakage. Anhydrous ammonia is the primary heat transfer fluid aboard the station, providing critical thermal management of habitat and payload systems. The solar radiator joints, as well as the various payload pointing systems, are obvious examples of the need for a reliable fluid transfer device. Low weight, tight temperature control, low parasitic drag torque, long life, and high reliability, in addition to near zero leakage, are important characteristics necessary for the successful operation of such a device. In late 1986, Lockheed initiated a project to develop a Rotary Transfer Coupling (RTC) directed toward space station requirements. Fabrication and assembly of this device is now complete and testing is scheduled. The design and development of the face seal-type rotary fluid coupling that utilizes a unique cover gas concept (an inert gas such as nitrogen) to provide full containment of the ammonia was addressed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Langley Research Center, The 22nd Aerospace Mechanisms Symposium; p 341-353
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    Vortex shedding experiment with flat and curved bluff plates in water (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Vortex shedding experiments were conducted in a water flow facility in order to simulate the strong discrete 4000-Hz vibration detected in the Space Shuttle Main Engine (SSME) which is thought to be associated with the SSME LOX inlet tee splitter vanes on the Main Injector. For the case of a flat vane with a blunt trailing edge excited by flow induced vortex shedding, lock-in with the first bending mode of the plate was observed. A curved vane displayed similar behavior, with the lock-in being a more discrete higher amplitude response. Aluminum vanes were employed to decouple the first vane bending mode from the vortex shedding mode. The application of an asymmetric 30-deg trailing edge bevel to both the flat and curved vanes was found to greatly reduce the strength of the shed vortices.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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    Acoustics and dynamics of coaxial interacting vortex rings (1988)
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    Publication Date: 2011-08-19
    Description: Using a contour dynamics method for inviscid axisymmetric flow we examine the effects of core deformation on the dynamics and acoustic signatures of coaxial interacting vortex rings. Both 'passage' and 'collision' (head-on) interactions are studied for initially identical vortices. Good correspondence with experiments is obtained. A simple model which retains only the elliptic degree of freedom in the core shape is used to explain some of the calculated features.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Fluid Dynamics Research (ISSN 0169-5983); 3; 1-4,
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    Nonlinear spatial evolution of an externally excited instability wave in a free shear layer (1988)
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    Publication Date: 2011-08-19
    Description: This paper considers a disturbance evolving from a strictly linear finite-growth-rate instability wave, with nonlinear effects first becoming important in the critical layer. By incorporating viscous effects into the nonlinear critical-layer analysis of Goldstein and Leib (1988), it was possible to demonstrate how an initially linear instability wave evolves as it propagates downstream and how the viscous effects eventually become important, even when the viscosity is very small, due to continually decreasing scales generated by the nonlinear effects.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 197; 295-330
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    The mean flow structure around and within a turbulent junction or horseshoe vortex. I - The upstream and surrounding three-dimensional boundary layer (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An experimental study of the mean flow structure upstream, around, and in a turbulent junction or horseshoe vortex is presented for the case of an incompressible subsonic flow. Mean velocity field and turbulent kinetic energy field measurements (obtained with hot film anemometry) and local wall shear stress measurements are used to monitor the upstream and surrounding three-dimensional turbulent boundary layer-like flow away from separation. Freestream or edge velocity and floor static pressure results are reported.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: ASME, Transactions, Journal of Fluids Engineering (ISSN 0098-2202); 110; 406-414
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    Observations of the frequencies in a sphere wake and of drag increase by acoustic excitation (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Vortex shedding and instability wave frequencies have been measured in the wakes of spheres in the Reynolds number range 500 less than Re less than 60,000. The effect of acoustic excitation was examined and an interaction between the two frequency modes was found at the lower Reynolds numbers; through this interaction, external forcing at the instability frequency could change the vortex shedding frequency. The development of the mean wake was manipulated by forcing near to the dominant shear layer instability frequency. With this forcing, the separated shear layer moved closer to the surface of the sphere and the reversed flow region of the wake was shortened. Concomitantly, the base pressure decreased and drag increased.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids (ISSN 0031-9171); 31; 3260-326
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    Investigation of the flow between a pair of circular cylinders in the flopping regime (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The wakes of a pair of circular cylinders are grossly unsteady when the cylinders are separated in a direction normal to the approaching flow by less than one cylinder diameter. The wakes flop randomly between two asymmetric states. The time-scale for the flopping is several orders of magnitude longer than the timescale of vortex shedding, and also several orders of magnitude longer than the timescale for instability of the separating shear layers. When a splitter plate is positioned suitably on the centerline of the cylinders, the flopping can be stopped and the flow made to assume either of the asymmetric states, or a symmetric steady state. For a range of plate positions a new, periodic oscillation occurs. Acoustic excitation can also destroy the flopping mean flow, replacing it by a symmetric flow.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 196; 431-448
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    Sources of error in the graphical analysis of CFD results (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Errors inherent to the graphic analysis of CFD solutions are discussed. Consideration is given to contouring, plotting of vector fields, particle tracing, and the computation of flow functions involving integration or differentiation. Many of the problems addressed are the direct result of knowing the function values only at grid points, not in the interior of the grid cells.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Scientific Computing (ISSN 0885-7474); 3; 149-164
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    Application of advanced computational technology to propulsion CFD (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The Internal Fluid Mechanics Division of the NASA Lewis Research Center is combining the key elements of computational fluid dynamics, aerothermodynamic experiments, and advanced computational technology to bring internal computational fluid dynamics (ICFM) to a state of practical application for aerospace propulsion system design. This paper presents an overview of efforts underway at NASA Lewis to advance and apply computational technology to ICFM. These efforts include the use of modern, software engineering principles for code development, the development of an AI-based user-interface for large codes, the establishment of a high-performance, data communications network to link ICFM researchers and facilities, and the application of parallel processing to speed up computationally intensive and/or time-critical ICFM problems. A multistage compressor flow physics program is cited as an example of efforts to use advanced computational technology to enhance a current NASA Lewis ICFM research program.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Computers and Structures (ISSN 0045-7949); 30; 1-2,; 375-384
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    Numerical simulation methods of incompressible flows and an application to the Space Shuttle main engine (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper discusses incompressible Navier-Stokes solution methods with an emphasis on the pseudocompressibility method. A steady-state flow solver based on the pseudocompressibility approach is then described. This flow solver code has been used to analyze the internal flow in the Space Shuttle main engine hot-gas manifold. Salient features associated with this three-dimensional realistic flow simulation are discussed. Numerical solutions relevant to the current engine analysis and the redesign effort are discussed along with experimental results. This example demonstrates the potential of computational fluid dynamics as a design tool for aerospace applications.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal for Numerical Methods in Fluids (ISSN 0271-2091); 8; 1241-126
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    Simple high-accuracy resolution program for convective modelling of discontinuities (1988)
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    Publication Date: 2011-08-19
    Description: For steady multidimensional convection, the Quadratic Upstream Interpolation for Convective Kinematics (QUICK) scheme has several attractive properties. However, for highly convective simulation of step profiles, QUICK produces unphysical overshoots and a few oscillations, and this may cause serious problems in nonlinear flows. Fortunately, it is possible to modify the convective flux by writing the normalized convected control-volume face value as a function of the normalized adjacent upstream node value, developing criteria for monotonic resolution without sacrificing formal accuracy. This results in a nonlinear functional relationship between the normalized variables, whereas standard methods are all linear in this sense. The resulting Simple High Accuracy Resolution Program (SHARP) can be applied to steady multidimensional flows containing thin shear or mixing layers, shock waves, and other frontal phenomena. This represents a significant advance in modeling highly convective flows of engineering and geophysical importance. SHARP is based on an explicit, conservative, control-volume flux formation, equally applicable to one, two, or three dimensional elliptic, parabolic, hyperbolic, or mixed-flow regimes. Results are given for the bench-mark purely convective first-order results and the nonmonotonic predictions of second- and third-order upwinding.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal for Numerical Methods in Fluids (ISSN 0271-2091); 8; 1291-131
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    A spectral multi-domain technique for viscous compressible reacting flows (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The first application of a spectral multidomain method for viscous compressible flow is presented. The method imposes a global flux balance condition at the interface so that high-order continuity of the solution is preserved. The solution scheme can be adapted to the particular requirement in each subdomain. To illustrate these advantages, a Mach 11 shock calculation is presented to study the chemical kinetics initiated as air passes through a fully resolved shock wave.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal for Numerical Methods in Fluids (ISSN 0271-2091); 8; 1121-113
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    The mean flow structure around and within a turbulent junction or horseshoe vortex. II - The separated and junction vortex flow (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Five-hole probe measurements of the flow through the separation region and in the vortex system of an incompressible subsonic flow around and within a turbulent junction or horseshoe vortex are reported. Mean velocity, static pressure, and total pressure results are presented. The streamwise vorticity field is obtained from the measured velocity field. Flow visualization results for the floor and cylinder surface agree well with the flow field data.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: ASME, Transactions, Journal of Fluids Engineering (ISSN 0098-2202); 110; 415-423
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    Thermal conductance of pressed aluminum and stainless steel contacts at liquid helium temperatures (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The thermal conductance of aluminum and stainless steel 304 sample pairs with surface finishes ranging from 0.1 to 1.6 microns rms roughness was investigated over a temperature range from 1.6 to 6.0 K. The thermal conductance follows a simple power law function of temperature, with the exponent ranging from 0.5 to 2.25, increases asymptotically with increasing applied force, and exhibits an anomaly for surface finishes in the 0.4 micron region.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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    On the wind force needed to dislodge a drop adhered to a surface (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The dislodging by dynamic pressure forces of a drop adhered by surface tension to a plane is considered. The method involves the numerical solution of the integrodifferential equation describing the drop shape and the obtaining of the critical Weber number as a function of contact angle hysteresis. The study assumes high-Reynolds-number free-streamline separation from the drop.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 196; 205-222
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    Instabilities caused by oscillating accelerations normal to a viscous fluid-fluid interface (1988)
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    Publication Date: 2011-08-19
    Description: The case of two incompressible viscous fluids (with different densities) which meet at a planar interface and are subject to an externally imposed oscillating acceleration directed normal to the interface is studied. The linear evolution of perturbations to the basic-state flow is investigated. It is found that the critical Stokes-Reynolds number and the most unstable perturbation wavelengths are insensitive to the degree of density and viscosity differences between the two fluids.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 196; 495-511
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    An adaptive finite element solver for transient problems with moving bodies (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The combination of adaptive remeshing techniques, flow solvers for transient problems with moving grids, and integrators for rigid body motion is presented. The resulting scheme allows the economic simulation of fully coupled fluid-rigid body interaction problems of arbitrary geometric complexity. Several results are given to demonstrate the capabilities developed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Computers and Structures (ISSN 0045-7949); 30; 1-2,; 303-317
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    Experiments for the determination of convective diffusion heat/mass transfer to burner rig test targets comparable in size to jet stream diameter (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The application of a recently formulated vapor transport theory to predict deposition rates of corrosive salts from alkali-seeded combustion gases of a small-capacity, high-velocity, atmospheric-pressure burner rig was hampered by the relatively large dimensions of the cylindrical deposit collector compared to the diameter of the combustion gas stream. The relative dimensions lead to a highly nonadiabatic combustion gas flow around the collector and necessitate two series of experiments. In the first series, mass transfer coefficients are determined by utilizing the naphthalene sublimation technique. The second series of experiments determines the dilution effect on the sodium species concentrations due to the entrainment of ambient air. This second series involves the measurement of the temperature variation along the surface of the collector under steady state conditions. Vapor deposition rates are determined exploiting this information and the results are found to compare favorably with experimentally obtained rates.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: ASME, Transactions, Journal of Heat Transfer (ISSN 0022-1481); 110; 442-448
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    Computational aspects of heat transfer in structures via transfinite-element formulations (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 2; 189-192
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  • 91
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    Nonlinear roll-up of externally excited free shear layers (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The effects of strong critical-layer nonlinearity on the spatially growing instabilities of a shear layer between two parallel streams are considered. A composite expansion technique is used to obtain a single formula that accounts for both shear-layer spreading and nonlinear critical-layer effects. Nonlinearity causes the instability to saturate well upstream of the linear neutral stability point. It also produces vorticity roll-up that cannot be predicted by linear theory.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 191; 481-515
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  • 92
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    A new hybrid transfinite element computational methodology for applicability to conduction/convection/radiation heat transfer (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper describes new and recent advances in the development of a hybrid transfinite element computational methodology for applicability to conduction/convection/radiation heat transfer problems. The transfinite element methodology, while retaining the modeling versatility of contemporary finite element formulations, is based on application of transform techniques in conjunction with classical Galerkin schemes and is a hybrid approach. The purpose of this paper is to provide a viable hybrid computational methodology for applicability to general transient thermal analysis. Highlights and features of the methodology are described and developed via generalized formulations and applications to several test problems. The proposed transfinite element methodology successfully provides a viable computational approach and numerical test problems validate the proposed developments for conduction/convection/radiation thermal analysis.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal for Numerical Methods in Engineering (ISSN 0029-5981); 26; 1087-110
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  • 93
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    The fully nonlinear development of Goertler vortices in growing boundary layers (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A combination of asymptotic and numerical methods is used to study the fully nonlinear development of small-wavelength Goertler vortices in a growing boundary layer. It is shown that the vortices spread out across the boundary layer, effectively driving the boundary layer, and that the mean flow adjusts so as to make the large-amplitude vortices locally neutral. In the region where the vortices exist, the mean flow is found to have a square-root profile, and the vortex velocity field can be written in closed form. The region of vortex activity is shown to ultimately include almost all of the original boundary layer and much of the free stream.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Proceedings, Series A - Mathematical and Physical Sciences (ISSN 0080-4630); 415; 1849,; 421-444
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    Slip effects associated with Knudsen transport phenomena in porous media (1988)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: Porous media used in phase separators and thermomechanical pumps have been the subject of characterization efforts based on the Darcy permeability of laminar continuum flow. The latter is not always observed at low speed, in particular at permeabilities below 10 to the -9th/squared cm. The present experimental and theoretical studies address questions of slip effects associated with long mean free paths of gas flow at room temperature. Data obtained are in good agreement, within data uncertainty, with a simplified asymptotic Knudsen equation proposed for porous plugs on the basis of Knudsen's classical flow equation for long mean free paths.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Cryogenics (ISSN 0011-2275); 28; 110-114
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    Analytical study of He II flow characteristics in the SHOOT transfer line (1988)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: Pressure and temperature profiles for He II flow in the transfer line for the Superfluid Helium On-Orbit Transfer (SHOOT) experiment are determined using a finite difference method to solve the one-dimensional two-fluid conservation equations. For practical purposes, forced flow of He II with Re greater than 10 to the 6th can be treated as a classical turbulent flow For a maximum SHOOT transfer rate of 800 cu dm/h, the temperature rise between the pump outlet and the receiver tank is about 80 mk with a 7-W heat load imposed on the 4-m-long transfer line. A pump outlet pressure of 160 torr is required to sustain the 800 cu dm/h flow without causing vapor formation within the transfer line.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Cryogenics (ISSN 0011-2275); 28; 81-85
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  • 96
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    Measured and predicted shock shapes for AFE configuration at Mach 6 in air and in CF4 (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Shock shapes and stand-off distances were obtained for the Aeroassist Flight Experiment configuration from Mach 6 tests in air and in CF4. Results were plotted for an angle-of attack range from -10 to 10 degrees and comparisons were made at selected angles with inviscid-flow predictions. Tests were performed in the Langley Research Center (LaRC) 20 inch Mach 6 Tunnel (air) at unit free-stream Reynolds numbers (N sub Re, infinity) of 2 million/ft and 0.6 million/ft and in the LaRC Hypersonic CF4 Tunnel at N sub Re, infinity = 0.5 million/ft and 0.3 million/ft. Within the range of these tests, N sub Re, infinity did not affect the shock shape or stand off distance, and the predictions were in good agreement with the measurements. The shock stand-off distance in CF4 was approximately half of that in air. This effect resulted from the differences in density ratio across the normal shock, which was approximately 12 in CF4 and 5 in air. In both test gases, the shock lay progressively closer to the body as angle of attack decreased.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-100660 , NAS 1.15:100660
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    Direct numerical simulation of compressible free shear flows (1988)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: Direct numerical simulations of compressible free shear layers in open domains are conducted. Compact finite-difference schemes of spectral-like accuracy are used for the simulations. Both temporally-growing and spatially-growing mixing layers are studied. The effect of intrinsic compressibility on the evolution of vortices is studied. The use of convective Mach number is validated. Details of vortex roll up and pairing are studied. A simple explanation of the stabilizing effect of compressibility is offered. Acoustic radiation from vortex roll up, pairing and shape oscillations is studied and quantified.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Sandia National Labs., Summary of Discussions at the Eleventh Meeting of the Sandia Cooperative Group on the Aerothermochemistry of Turbulent Combustion; p 23
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  • 98
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    A comparative study and validation of upwind and central-difference Navier-Stokes codes for high-speed flows (1988)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: A comparative study was made using 4 different computer codes for solving the compressible Navier-Stokes equations. Three different test problems were used, each of which has features typical of high speed internal flow problems of practical importance in the design and analysis of propulsion systems for advanced hypersonic vehicles. These problems are the supersonic flow between two walls, one of which contains a 10 deg compression ramp, the flow through a hypersonic inlet, and the flow in a 3-D corner formed by the intersection of two symmetric wedges. Three of the computer codes use similar recently developed implicit upwind differencing technology, while the fourth uses a well established explicit method. The computed results were compared with experimental data where available.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AGARD, Validation of Computational Fluid Dynamics. Volume 1: Symposium Papers and Round Table Discussion; 15 p
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    CFD validation experiments for internal flows (1988)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Computational Fluid Dynamics (CFD) validation experiments at NASA Lewis are described. The material presented summarized the research in 3 areas: Inlets, ducts and nozzles; Turbomachinery; and Chemically reacting flows. The specific validation activities are concerned with shock boundary layer interactions, vortex generator effects, large low speed centrifugal compressor measurements, transonic fan shock structure, rotor/stator kinetic energy distributions, stator wake shedding characteristics, boundary layer transition, multiphase flow and reacting shear layers. These experiments are intended to provide CFD validation data for the internal flow fields within aerospace propulsion system components.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AGARD, Validation of Computational Fluid Dynamics. Volume 1: Symposium Papers and Round Table Discussion; 13 p
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    Accurate solutions, parameter studies and comparisons for the Euler and potential flow equations (1988)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Parameter studies are conducted using the Euler and potential flow equation models for steady and unsteady flows in both two and three dimensions. The Euler code is an implicit, upwind, finite volume code which uses the Van Leer method of flux vector splitting which has been recently extended for use on dynamic meshes and maintain all the properties of the original splitting. The potential flow code is an implicit, finite difference method for solving the transonic small disturbance equations and incorporates both entropy and vorticity corrections into the solution procedures thereby extending its applicability into regimes where shock strength normally precludes its use. Parameter studies resulting in benchmark type calculations include the effects of spatial and temporal refinement, spatial order of accuracy, far field boundary conditions for steady flow, frequency of oscillation, and the use of subiterations at each time step to reduce linearization and factorization errors. Comparisons between Euler and potential flow results are made, as well as with experimental data where available.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AGARD, Validation of Computational Fluid Dynamics. Volume 1: Symposium Papers and Round Table Discussion; 16 p
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