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  • Inorganic Chemistry  (693)
  • FLUID MECHANICS AND HEAT TRANSFER  (633)
  • 1995-1999
  • 1990-1994  (1,326)
  • 1950-1954
  • 1990  (1,326)
Collection
Keywords
Publisher
Years
  • 1995-1999
  • 1990-1994  (1,326)
  • 1950-1954
Year
  • 1
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    An error analysis of least-squares finite element method of velocity-pressure-vorticity formulation for Stokes problem (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A theoretical proof of the optimal rate of convergence for the least-squares method is developed for the Stokes problem based on the velocity-pressure-vorticity formula. The 2D Stokes problem is analyzed to define the product space and its inner product, and the a priori estimates are derived to give the finite-element approximation. The least-squares method is found to converge at the optimal rate for equal-order interpolation.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Computer Methods in Applied Mechanics and Engineering (ISSN 0045-7825); 84; 3, De
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  • 2
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    Experimental and computational surface and flow-field results for an all-body hypersonic aircraft (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: Personnel from NASA Ames Research Center presented a paper on establishing a benchmark experimental data base for generic hypersonic vehicle shape for validation and/or calibration of advanced computational fluid dynamics computer codes. The need for this capability is based on a requirement for extensive hypersonic data to fully validate CFD codes to be used for NASP and other hypersonic vehicles. The use of wind tunnel models in the Ames 3.5-ft Hypersonic Wind Tunnel to obtain pertinent surface and flow-field data over a broad range of test conditions is described.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Lewis Research Center, 2nd NASA CFD Validation Workshop; p 126-161
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  • 3
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    NASA. Lewis Research Center/IFMD inlet duct and nozzle high speed validation experiments (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: Personnel from NASA Lewis Research Center spoke on the subject of inlet duct and nozzle high speed validation experiments to include crossing shocks and boundary layer interaction, unsteady shock/boundary layer interactions, and vortex generators. Attention was also paid to the subjects of high speed mixing and transition ducts. Specific application was made to the NASP hypermixing concepts.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: 2nd NASA CFD Validation Workshop; p 197-231
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  • 4
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    Summary of NASA. Lewis Research Center validation efforts (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: NASA Lewis Research Center personnel presented a summary of LeRC validation experiments. The subjects discussed included: iced wing, linear transonic cascade, transition duct aerodynamics, transition duct heat transfer, low speed centrifugal compressor, turbomachinery blade row interactions, and three dimensional fluid mechanics.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: 2nd NASA CFD Validation Workshop; p 100-125
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  • 5
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    NASA. Langley Research Center CFD code validation program overview (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: A presentation by Langley Research Center covered subjects of: LaRC approach to CFD code validation, experimental CFD perceptions, CFD code validation program experiment, and highlights of the experiment. The objective of the validation program and the approach taken are discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Lewis Research Center, 2nd NASA CFD Validation Workshop; p 1-21
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  • 6
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    NASA low speed centrifugal compressor (1990)
    In:  CASI
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    Publication Date: 2004-12-04
    Description: The flow characteristics of a low speed centrifugal compressor were examined at NASA Lewis Research Center to improve understanding of the flow in centrifugal compressors, to provide models of various flow phenomena, and to acquire benchmark data for three dimensional viscous flow code validation. The paper describes the objectives, test facilities' instrumentation, and experiment preliminary comparisons.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: 2nd NASA CFD Validation Workshop; p 232-256
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  • 7
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    Flow over a rearward facing step (1990)
    In:  CASI
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    Publication Date: 2004-12-04
    Description: The characteristics of flow over a rearward facing step is discussed in a paper presented by NASA Lewis Research Center personnel. The objective is to obtain data which will be used for validation of Direct Numerical Simulations being developed at NASA Langley and Ames. Two phases of the work are identified as a study of large scale structures in the flow using hot-wire/cold wire techniques and the development of a statistical data base for using three-component laser velocimetry.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Lewis Research Center, 2nd NASA CFD Validation Workshop; p 182-196
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  • 8
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    Overview of CFD flow modeling and validation: NASA. Ames Research Center (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: NASA Ames Center personnel presented data on stages of code development and corresponding experiments in the application of computational fluid dynamics for aeronautical investigations. Specific subjects included algorithms, grid generation, facilities, instrumentation, and data acquisition. Numerical simulation and flow modelling were described to show the procedure for calibration and validation.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Lewis Research Center, 2nd NASA CFD Validation Workshop; p 45-69
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  • 9
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    Status of NASA. Marshall Space Flight Center CFD application and validation activities (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: NASA Marshall Space Flight Center personnel presented a paper on the status of MSFC computational fluid dynamics application and validation activities. Subjects discussed included the Space Shuttle Main Engine studies, unsteady multistage turbine loads, fuel pump discharge volutes, and injector LOX inlet results based on fundamental flows, subcomponents, and interactive components/systems.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Lewis Research Center, 2nd NASA CFD Validation Workshop; p 70-99
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  • 10
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    Fluid management in the optimization of space construction (1990)
    In:  CASI
    Details
    Publication Date: 2004-10-02
    Description: Fluid management impacts strongly on the optimization of space construction. Large quantities of liquids are needed for propellants and life support. The mass of propellant liquids is comparable to that required for the structures. There may be a strong dynamic interaction between the stored liquids and the space structure unless the design minimizes the interaction. The constraints of cost and time required optimization of the supply/resupply strategy. The proper selection and design of the fluid management methods for: slosh control; stratification control; acquisition; transfer; gauging; venting; dumping; contamination control; selection of tank configuration and size; the storage state and the control system can improve the entire system performance substantially. Our effort consists of building mathematical/computer models of the various fluid management methods and testing them against the available experimental data. The results of the models are used as inputs to the system operations studies. During the past year, the emphasis has been on modeling: the transfer of cryogens; sloshing and the storage configuration. The work has been intermeshed with ongoing NASA design and development studies to leverage the funds provided by the Center.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Second Annual Symposium; p 412-433
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  • 11
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    Unstructured finite element mesh generation and adaptive procedures for CFD (1990)
    In:  CASI
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    Publication Date: 2011-10-14
    Description: A method is described for generating unstructured meshes of triangles or tetrahedra for computational domains of complex geometrical shape. To illustrate the power of the approach, it is applied to the solution of flows past several complete aircraft configurations. The advocated approach allows for the natural incorporation of mesh adaptivity and this is demonstrated for both inviscid and viscous computations in two and three dimensions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AGARD, Applications of Mesh Generation to Complex 3-D Configurations; 12 p
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  • 12
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    Applications of algebraic grid generation (1990)
    In:  CASI
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    Publication Date: 2011-10-14
    Description: Techniques and applications of algebraic grid generation are described. The techniques are univariate interpolations and transfinite assemblies of univariate interpolations. Because algebraic grid generation is computationally efficient, the use of interactive graphics in conjunction with the techniques is advocated. A flexible approach, which works extremely well in an interactive environment, called the control point form of algebraic grid generation is described. The applications discussed are three-dimensional grids constructed about airplane and submarine configurations.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AGARD, Applications of Mesh Generation to Complex 3-D Configurations; 12 p
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  • 13
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    A defect stream function formulation for compressible turbulent boundary layers (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Progress to date on the development of a method for turbulent, wall-bounded flow which uses the defect stream function formulation in the outer layer and an analytic law of the wall and wake formulation in the inner region is reviewed. This two-formulation approach avoids the need to computationally resolve the high-gradient inner layer. One of the most appealing recent developments is the transformation of the compressible governing equation for the defect stream function into a linear, second-order differential equation which has analytic solutions for many problems of practical interest. Numerical and analytic results for incompressible and compressible flows are shown to be in excellent agreement with experimental results. In this paper the two-formulation approach is applied to primitive-variable computations. Excellent comparisons with experiment are presented for two compressible flat plate flows.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 14
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    Quasi-coherent structures in the turbulent boundary layer. II - Verification and new information from a numerically simulated flat-plate layer (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 15
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    Velocity and pressure fields associated with near-wall turbulence structures (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Computer generated databases containing velocity and pressure fields in three-dimensional space at a sequence of time-steps, were used for the investigation of near-wall turbulence structures, their space-time evolution, and their associated pressure fields. The main body of the results were obtained from simulation data for turbulent channel flow at a Reynolds number of 180 (based on half-channel height and friction velocity) with a grid of 128 x 129 x and 128 points. The flow was followed over a total time of 141 viscous time units. Spanwise centering of the detected structures was found to be essential in order to obtain a correct magnitude of the associated Reynolds stress contribution. A positive wall-pressure peak is found immediately beneath the center of the structure. The maximum amplitude of the pressure pattern was, however, found in the buffer region at the center of the shear-layer. It was also found that these flow structures often reach a maximum strength in connection with an asymmetric spanwise motion, which motivated the construction of a conditional sampling scheme that preserved this asymmetry.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 16
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    Quasi-coherent structures in the turbulent boundary layer. I - Status report on a community-wide summary of the data (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A review is presented of the approach, motivation and early results of a reevaluation of the knowledge collected by the research community during thirty years of research on the structure of turbulent boundary layers. Four distinctions or criteria concerning the need to improve the practices in this field are discussed: data versus inferences, possible versus actual versus significant events, one structure versus many, and one or two flows versus the totality of data. Attention given to the known quasi-coherent structures show that three factors significantly reduce the information available from laboratory data as a basis for forming a complete model of the quasi-coherent structure in the turbulent boundary layer: (1) the necessity to ensemble average probe output with resulting loss of phase information, (2) the inability to see more than one or two of the various types of structures simultaneously, and (3) the inability to see the spatial relations between the various quasi-coherent structures resulting from (1) and (2).
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 17
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    Statistical analysis of near-wall structures in turbulent channel flow (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The two-point correlation tensor is used to analyze near-wall structures in turbulent channel flow. Simulation results have been utilized to obtain the correlation tensor with sufficient spatial resolution to permit accurate differentiation for computing the vorticity correlation, and the resolution of sharp features such as the shear layer and its corresponding region of spanwise vorticity. Proper orthogonal decomposition and stochastic estimation were observed to yield similar results when appropriate conditions were employed for the estimation. Resulting structures were such that they would be detected by standard conditional sampling methods. The results of decomposing the vorticity field and the velocity field were significantly different, indicating that if a coherent structure is found that dominates the velocity fields, the curl of that velocity structure will not dominate the vorticity field.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 18
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    Similarity of organized structures in turbulent shear flows (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Recent analysis of databases generated by direct numerical simulations of homogeneous turbulent shear flows have revealed the presence of coherent structures similar to those in turbulent boundary layers. In this paper these findings and tentative conclusions on their significance are discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 19
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    Unsteady viscous flow around a circular cylinder found by the hopscotch scheme on a vector processing machine (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The hopscotch scheme is examined to see whether it can compete effectively with implicit schemes for the integration of the Navier-Stokes equations on a vector processing machine. This scheme is stable as long as the Courant number is less than or equal to one and it does not underestimate viscous effects. The accuracy of the scheme is tested on one- and two-dimensional problems whose exact solutions are known. The scheme is then used to simulate flows around a circular cylinder with Reynolds numbers 200, 500 and 1000.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Applied Numerical Mathematics (ISSN 0168-9274); 6; 195-208
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  • 20
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    Interfacial dynamics of two liquids under an oscillating gravitational field (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The evolution of two miscible liquids meeting at an initially sharp interface inside a cavity under microgravity g-jitter conditions is studied numerically. The response of the interface and kinematics of the flowfield to various g-jitter accelerations and aspect ratio variations is shown. The interface region acts like a vortex source sheet, and it can be unstable to Kelvin-Helmholtz and Rayleigh-Taylor instabilities. The vortices produced along the interface can serve as a stirring mechanism to promote local mixing. Below the critical Stokes-Reynolds number, the destabilization of the interface results in deformation into wavy structures. In some parameter regions, these structures oscillate in time; in others, they are quasi-steady. Above the critical Stokes-Reynolds number, 'chaotic' instability results, and the interface breaks into concentration pockets. The morphology of the initial breakup is similar to observed Rayleigh-Taylor instability. Subsequent mixing of the two fluids after the breakup of the interface is then very rapid.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 28; 1933-194
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  • 21
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    Stability of an oscillated fluid with a uniform density gradient (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Instabilities in a fluid with a constant density gradient that is subject to arbitrarily oriented oscillatory accelerations are considered. With the Boussinesq approximation and for the case of an unbounded fluid, transformation to Lagrangian coordinates allows the reduction of the problem to an ordinary differential equation for each three-dimensional wavenumber. The problem has three parameters: the nondimensional amplitude R of the base-state oscillation, the nondimensional level of background steady acceleration, which for some cases can be represented in terms of a local (in time) Richardson number Ri, and the Prandtl number Pr. Some general bounds on stability are derived. For Pr = 1 closed-form solutions are found for impulse (delta function) accelerations and a general asymptotic solution is constructed for large R and general imposed accelerations. The asymptotic solution takes advantage of the fact that at large R wave growth is concentrated at 'zero points'. These are times when the effective vertical wavenumber passes through zero. Kelvin-Helmholtz instabilities are found to dominate at low R, while Rayleigh-Taylor instabilities dominate at high R. At high R, the uniform shear of the Kelvin-Helmholtz case tends to distort and weaken instability waves. With unsteady flows, Ri = 1/4 is no longer an instability limit. Significant instabilities have been found for sinusoidal forcing for Ri up to 0.6.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 219; 449-468
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  • 22
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    Riblets (1990)
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    Publication Date: 2011-08-19
    Description: In addition to characterizing the various concepts reported in the literature on longitudinally-ribbed surface for aerodynamic surface drag reduction, the present development status evaluation of this technology correlates all available experimental data. An analysis of these data is then conducted to ascertain the parameters most directly involved in drag reduction, and to evaluate the effects which have thus far been exerted on turbulent boundary layer structures. Such advanced riblet techniques as compound and three-dimensional riblets, riblets in combination with large-eddy breakup devices, and riblets with suction/blowing, are also discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 23
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    Active wave control of boundary-layer transition (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The physical processes involved in the boundary layer instability-generation and transition process seem to pose basic restrictions on the implementation of active, wave-based transition-control methods. While suppression short of elimination is possible by these means for primary disturbances, wave-interaction instabilities demand that the control be implemented almost immediately after the appearance of primary disturbances; even slight delays can negate the intended beneficial effects, and this basic problem is exacerbated at the higher Reynolds numbers typical of aircraft in cruising flight. Three-dimensional disturbances are noted to be important in this context, together with the continuous regeneration of TS waves.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 24
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    Recent advances, trends and new perspectives via enthalpy-based finite element formulations for applications to solidification problems (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The present paper describes recent advances and trends in finite element developments and applications for solidification problems. In particular, in comparison to traditional methods of approach, new enthalpy-based architectures based on a generalized trapezoidal family of representations are presented which provide different perspectives, physical interpretation and solution architectures for effective numerical simulation of phase change processes encountered in solidification problems. Various numerical test models are presented and the results support the proposition for employing such formulations for general phase change applications.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal for Numerical Methods in Engineering (ISSN 0029-5981); 30; 803-820
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  • 25
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    Inviscid flux-splitting algorithms for real gases with non-equilibrium chemistry (1990)
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    Publication Date: 2011-08-19
    Description: Formulations of inviscid flux splitting algorithms for chemical nonequilibrium gases are presented. A chemical system for air dissociation and recombination is described. Numerical results for one-dimensional shock tube and nozzle flows of air in chemical nonequilibrium are examined.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 90; 371-395
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  • 26
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    Ternary baroeffect with a nondiffusing component (1990)
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    Publication Date: 2011-08-19
    Description: A systematic analysis is developed which describes the isothermal counterdiffusion of two gases in the presence of a third nondiffusing gas. Four distinct regimes are identified for diffusive slip. The nondiffusing gas reduces the pressure drop in all cases, whether it raises or lowers the mean density. The gas leads to nonzero diffusive slip even in the limit of very disparate masses for the diffusing gases. The implications of these findings for controlling concentration creep in crystal growth are discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physical Review Letters (ISSN 0031-9007); 65; 1587-159
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  • 27
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    Diagonally inverted lower-upper factored implicit multigrid scheme for the three-dimensional Navier-Stokes equations (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 28; 1642-164
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  • 28
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    Solitons induced by boundary conditions from the Boussinesq equation (1990)
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    Publication Date: 2011-08-19
    Description: The behavior of solitons induced by boundary excitation is investigated at various time-dependent conditions and different unperturbed water depths, using the Korteweg-de Vries (KdV) equation. Then, solitons induced from Boussinesq equations under similar conditions were studied, making it possible to remove the restriction in the KdV equation and to treat soliton head-on collisions (as well as overtaking collisions) and reflections. It is found that the results obtained from the KdV and the Boussinesq equations are in good agreement.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 1574-158
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  • 29
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    Hopf bifurcation in the driven cavity (1990)
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    Publication Date: 2011-08-19
    Description: The algorithm employed in the present incompressible two-dimensional calculations of an impulsively-started lid-driven cavity has its basis in the time-dependent stream-function equation. While a Crank-Nicholson differencing scheme is used for the diffusion terms, the Adams-Bashforth scheme is used for the convection terms. The periodic asymptotic solutions obtained for Reynolds numbers of 5000 and 10,000 are found to be precisely periodic; it is demonstrated that they have reached asymptotic states. The indicators of that achievement are discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 90; 219-261
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  • 30
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    Containments for liquids at zero gravity (1990)
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    Publication Date: 2011-08-19
    Description: A theory proposed by Concus and Finn (1974) and recently developed by Finn (1983 and 1984) yields explicit geometrical criteria for the position of the free surface of a liquid at zero gravity in a cylindrical container of specified cross section. These criteria were applied by Concus and Finn to three container geometries: the bathtub, the trapezoid, and the keyhole. It is possible to find geometrical criteria that promise a liquid interface of finite height, with the base still covered with liquid, or a liquid interface of infinite height, with the liquid wetting a well defined portion of the wall. In the present work, calculations are presented for a fourth geometry, the non-concentric cylinders. In addition, the earlier calculations of Concus and Finn are extended, and a unified graphical presentation of all four geometries is given that can be used directly for the design of containments for liquids at zero gravity.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Microgravity Science and Technology (ISSN 0938-0108); 3; 13-23
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  • 31
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    A spectrum model for weakly anisotropic turbulence (1990)
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    Publication Date: 2011-08-19
    Description: A simple model, parameterized by the Reynolds stress anisotropy, is proposed for the spectrum of weakly anisotropic turbulence. It contains a model constant that affects its region of realizability. This spectrum model is used to derive a one-point closure to the rapid pressure-strain term. The derived pressure-strain model is linear in the Reynolds stress anisotropy and is of the same form as the closure model of Launder et al. (1975). The spectrum model becomes unrealizable in some regions of wave space for sufficiently large anisotropy of the Reynolds stress, and this is used to infer the region of validity of the linear closure model. It is found that the extent of the valid region is very small when the model constant is set to match rapid distortion theory, and largest for a model-constant set close to the value suggested by LRR. However, even the largest valid domain does not extend very far from isotropy, suggesting inherent weakness in the linear pressure-strain models.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 1500-150
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  • 32
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    A technique for measurement of instantaneous heat transfer in steady-flow ambient-temperature facilities (1990)
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    Publication Date: 2011-08-19
    Description: An experimental technique is described for obtaining time-resolved heat flux measurements with high-frequency response (up to 100 kHz) in a steady-flow ambient-temperature facility. The heat transfer test object is preheated and suddenly injected into an established steady flow. Thin-film gages deposited on the test surface detect the unsteady substrate surface temperature. Analog circuitry designed for use in short-duration facilities and based on one-dimensional semiinfinite heat conduction is used to perform the temperature/heat flux transformation. A detailed description of substrate properties, instrumentation, experimental procedure, and data reduction is given, along with representative results obtained in the stagnation region of a circular cylinder subjected to a wake-dominated unsteady flow. An in-depth discussion of related work is also provided.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Experimental Thermal and Fluid Science (ISSN 0894-1777); 3; 416-430
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    Near-wall turbulence model and its application to fully developed turbulent channel and pipe flows (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A near-wall turbulence model and its incorporation into a multiple-timescale turbulence model are presented. The near-wall turbulence model is obtained from a k-equation turbulence model and a near-wall analysis. In the method, the equations for the conservation of mass, momentum, and turbulent kinetic energy are integrated up to the wall, and the energy transfer and the dissipation rates inside the near-wall layer are obtained from algebraic equations. Fully developed turbulent channel and pipe flows are solved using a finite element method. The computational results compare favorably with experimental data. It is also shown that the turbulence model can resolve the overshoot phenomena of the turbulent kinetic energy and the dissipation rate in the region very close to the wall.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Numerical Heat Transfer, Part B: Fundamentals (ISSN 1040-7790); 17; 101-122
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    Implicit flux-split schemes for the Euler equations (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 28; 973
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  • 35
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    Numerical simulations of soft and hard turbulence - Preliminary results for two-dimensional convection (1990)
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    Publication Date: 2011-08-19
    Description: Results on the transition from soft to hard turbulence in simulations of two-dimensional Boussinesq convection are reported. The computed probability densities for temperature fluctuations are exponential in form in both soft and hard turbulence, unlike what is observed in experiments. In contrast, a change is obtained in the Nusselt number scaling on Rayleigh number in good agreement with the three-dimensional experiments.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physical Review Letters (ISSN 0031-9007); 64; 2370-237
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  • 36
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    Modeling of confined turbulent fluid-particle flows using Eulerian and Lagrangian schemes (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Two important aspects of fluid-particulate interaction in dilute gas-particle turbulent flows (the turbulent particle dispersion and the turbulence modulation effects) are addressed, using the Eulerian and Lagrangian modeling approaches to describe the particulate phase. Gradient-diffusion approximations are employed in the Eulerian formulation, while a stochastic procedure is utilized to simulate turbulent dispersion in the Lagrangina formulation. The k-epsilon turbulence model is used to characterize the time and length scales of the continuous phase turbulence. Models proposed for both schemes are used to predict turbulent fully-developed gas-solid vertical pipe flow with reasonable accuracy.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal of Heat and Mass Transfer (ISSN 0017-9310); 33; 691-701
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  • 37
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    The vibrating ribbon problem revisited (1990)
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    Publication Date: 2011-08-19
    Description: A revised formal solution of the vibrating ribbon problem of hydrodynamic stability is presented. The initial formulation of Gaster (1965) is modified by application of the Briggs method and a careful treatment of the complex double Fourier transform inversions. Expressions are obtained in a natural way for the discrete spectrum as well as for the four branches of the continuous spectra. These correspond to discrete and branch-cut singularities in the complex wavenumber plane. The solutions from the continuous spectra decay both upsteam and downstream of the ribbon, with the decay in the upstream direction being much more rapid than that in the downstream direction. Comments and clarification of related prior work are made.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 213; 531-547
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  • 38
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    Numerical analysis of three-dimensional viscous internal flows (1990)
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 28; 798-806
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  • 39
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    Variable specific heat and thermal relaxation parameter in hyperbolic heat conduction (1990)
    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); 4; 252-255
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  • 40
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    Implicit methods for the Navier-Stokes equations (1990)
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    Publication Date: 2011-08-19
    Description: Numerical solutions of the Navier-Stokes equations using explicit schemes can be obtained at the expense of efficiency. Conventional implicit methods which often achieve fast convergence rates suffer high cost per iteration. A new implicit scheme based on lower-upper factorization and symmetric Gauss-Seidel relaxation offers very low cost per iteration as well as fast convergence. High efficiency is achieved by accomplishing the complete vectorizability of the algorithm on oblique planes of sweep in three dimensions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Computing Systems in Engineering (ISSN 0956-0521); 1; 2-4,
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    Visualization of fluid dynamics at NASA Ames (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Some of the hardware and software tools and techniques in use at NASA's numerical aerodynamic simulation facility for the analysis of computational fluid dynamics are described. The visualization process can be illustrated by video tapes and stereo pictures. Although these visualization tools have dramatically improved the ability to conduct research in fluid dynamics, a comparison of the current environment for analysis with an 'ideal' environment illustrates that there are still major improvements that should be made. The most time-consuming task in future analyses of the increasingly complex computer simulations will be the extraction and clear display of the key features. In addition, the interface between the workstation and the scientist should be improved significantly. Current research on techniques for creating these improvements is described.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Computing Systems in Engineering (ISSN 0956-0521); 1; 2-4,
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  • 42
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    Nonlinear phase-space diffusion approach to turbulent organized structures (1990)
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    Publication Date: 2011-08-19
    Description: The study deals with the approximation of the effect of all velocity-increment moments on the spatial evolution of the pdf for maximally correlated structures by the effect of the second moment alone by assuming independence of separated length scales. The dependence of the two-point velocity statistics on length-scale or separation is found to be governed by the gradients of the stress, rather than of the velocity. This may provide a new approach for predicting the domain patterns observed in turbulent flows and a new means of characterizing or classifying different structures, namely, by their nonlinear diffusion coefficient.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Canadian Journal of Physics (ISSN 0008-4204); 68; 723-725
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  • 43
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    Effect of metallic coatings on the thermal contact conductance of turned surfaces (1990)
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    Publication Date: 2011-08-19
    Description: An experimental investigation was conducted to determine the degree to which the thermal contact conductance at the interface of contacting Aluminum 6061 T6 surfaces could be enhanced through the use of vapor-deposited metallic coatings. Three different coating materials (lead, tin, and indium) were evaluated using four different thicknesses for each coating material. The results verified the existence of an optimum coating thickness, shown to be in the range of 2.0 to 3.0 microns for indium, 1.5 to 2.5 microns for lead, and 0.2 to 0.5 microns for tin. The enhancement factors for thermal contact conductance were found to be on the order of 700, 400, and 50 percent, respectively. Based upon the experimental data, the hardness of the coating materials appears to be the most significant parameter in ranking the substrate and coating material combinations; however, additional experimental data are needed to substantiate this hypothesis. Finally, it was apparent that the thermal contact conductance enhancement effect was greatest at low contact pressures and decreased significantly with increases in the contact pressure.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: ASME, Transactions, Journal of Heat Transfer (ISSN 0022-1481); 112; 864-871
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    Influence of geometric features on the performance of pressure-swirl atomizers (1990)
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    Publication Date: 2011-08-19
    Description: The spray characteristics of several different simplex pressure-swirl nozzles are examined using water as the working fluid. Measurements of mean drop size, drop-size distribution, effective spray cone angle, and circumferential liquid distribution are carried out over wide ranges of injection pressure. Eight different nozzles are employed in order to achieve a wide variation in the length/diameter ratio of the final discharge orifice. Generally, it is found that an increase in discharge orifice length/diameter ratio, l(o)/d(o), increases the mean drop size in the spray and reduces the spray cone angle. The circumferential liquid distribution is most uniform when l(o)/d(o) = 2. If l(o)/d(o) is raised above or lowered below this optimum value, the circumferential uniformity of the liquid distribution is impaired. The observed effects of l(o)/d(o) on spray characteristics are generally the same regardless of whether the change in l(o)/d(o) is accomplished by varying l(o) or d(o).
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: ASME, Transactions, Journal of Engineering for Gas Turbines and Power (ISSN 0022-0825); 112; 579-584
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  • 45
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    Direct numerical simulation of a three-dimensional turbulent boundary layer (1990)
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    Publication Date: 2011-08-19
    Description: The effects of transverse strain on an initially two-dimensional turbulent boundary layer are studied in a direct numerical simulation of a planar channel flow with impulsively started transverse pressure gradient. Consistent with experiments in three-dimensional boundary layers, the simulation shows a decrease in the Reynolds shear stress with increasing transverse strain. Also, the directions of the Reynolds shear stress vector and the mean velocity gradient vector were found to differ. In addition, the simulation shows a drop in the turbulent kinetic energy. Terms in the Reynolds stress transport equations were computed. The balances indicate that the decrease in turbulent kinetic energy is a result of a decrease in turbulence production, along with an increase in turbulent dissipation. Intuitive reasoning and current turbulence models would predict an increase in kinetic energy along with increases in production and dissipation rates as a result of increased mean-flow strain rate. Later in the evolution of the flow, both turbulence production and dissipation increase.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 1846-185
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  • 46
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    Time-dependent boundary conditions for hyperbolic systems. II (1990)
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    Publication Date: 2011-08-19
    Description: A general boundary condition formalism is developed for all types of boundary conditions to which hyperbolic systems are subject; the formalism makes possible a 'cookbook' approach to boundary conditions, by means of which novel boundary 'recipes' may be derived and previously devised ones may be consulted as required. Numerous useful conditions are derived for such CFD problems as subsonic and supersonic inflows and outflows, nonreflecting boundaries, force-free boundaries, constant pressure boundaries, and constant mass flux. Attention is given to the computation and integration of time derivatives.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 89; 439-461
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  • 47
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    Long-wave morphological instabilities in the directional solidification of a dilute binary mixture (1990)
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    Publication Date: 2011-08-19
    Description: Long-wave instabilities in a directionally-solidified binary mixture may occur in several limits. Sivashinsky (1983) identified a small-segregation-coefficient limit and obtained a weakly nonlinear evolution equation governing subcritical two-dimensional bifurcation. Brattkus and Davis (1988) identified a near-absolute-stability limit and obtained a strongly nonlinear evolution equation governing supercritical two-dimensional bifurcation. The present investigation identifies a third strongly nonlinear evolution equation, arising in the small-segregation-coefficient, large-surface-energy limit. This equation links both of the former and describes the change from the sub- to super-critical bifurcations. This study sets the previous long-wave analyses into a logical framework.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: SIAM Journal on Applied Mathematics (ISSN 0036-1399); 50; 420-436
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  • 48
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    On the Lagrangian description of unsteady boundary-layer separation. II - The spinning sphere (1990)
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    Publication Date: 2011-08-19
    Description: A theory to explain the initial stages of unsteady separation was proposed by Van Dommelen and Cowley (1989). This theory is verified for the separation process that occurs at the equatorial plane of a sphere or a spheroid which is impulsively spun around an axis of symmetry. A Lagrangian numerical scheme is developed which gives results in good agreement with Eulerian computations, but which is significantly more accurate. This increased accuracy, and a simpler structure to the solution, also allows verification of the Eulerian structure, including the presence of logarithmic terms. Further, while the Eulerian computations broke down at the first occurrence of separation, it is found that the Lagrangian computation can be continued. It is argued that this separated solution does provide useful insight into the further evolution of the separated flow. A remarkable conclusion is that an unseparated vorticity layer at the wall, a familiar feature in unsteady separation processes, disappears in finite time.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 210; 627-645
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    Small-scale transition in a plane mixing layer (1990)
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    Publication Date: 2011-08-19
    Description: An experimental study was conducted to investigate the generation process of random small-scale turbulence in an originally laminar mixing layer. The evolutions of the two types of deterministic structures, the spanwise and streamwise vortices, were first clarified in order to determine their roles in the transition process. A scaling rule for the streamwise distance from the trailing edge of the splitter plate to the vortex merging position was found for various velocity ratios. After this stremwise lengthscale was determined, it became clear that the spanwise wavelength of the streamwise vortices doubled after the merging of the spanwise structures which nominally doubled streamwise wavelengths. The most interesting finding was that the random small-scale eddies were produced by the interactions between the merging spanwise structures and the streamwise vortices.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 210; 475-500
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  • 50
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    On the Lagrangian description of unsteady boundary-layer separation. I - General theory (1990)
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    Publication Date: 2011-08-19
    Description: Although unsteady, high-Reynolds number, laminar boundary layers have conventionally been studied in terms of Eulerian coordinates, a Lagrangian approach may have significant analytical and computational advantages. In Lagrangian coordinates the classical boundary layer equations decouple into a momentum equation for the motion parallel to the boundary, and a hyperbolic continuity equation (essentially a conserved Jacobian) for the motion normal to the boundary. The momentum equations, plus the energy equation if the flow is compressible, can be solved independently of the continuity equation. Unsteady separation occurs when the continuity equation becomes singular as a result of touching characteristics, the condition for which can be expressed in terms of the solution of the momentum equations. The solutions to the momentum and energy equations remain regular. Asymptotic structures for a number of unsteady 3-D separating flows follow and depend on the symmetry properties of the flow. In the absence of any symmetry, the singularity structure just prior to separation is found to be quasi 2-D with a displacement thickness in the form of a crescent shaped ridge. Physically the singularities can be understood in terms of the behavior of a fluid element inside the boundary layer which contracts in a direction parallel to the boundary and expands normal to it, thus forcing the fluid above it to be ejected from the boundary layer.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 210; 593-626
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    Multiple paths to subharmonic laminar breakdown in a boundary layer (1990)
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    Publication Date: 2011-08-19
    Description: Numerical simulations demonstrate that laminar breakdown in a boundary layer induced by the secondary instability of two-dimensional Tollmien-Schlichting waves to three-dimensional subharmonic disturbancews need not take the conventional lambda vortex/high-shear layer path.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physical Review Letters (ISSN 0031-9007); 64; 641-644
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    Time-accurate simulations of a shear layer forced at a single frequency (1990)
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 28; 267-275
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    Analysis of stability of a planar solid-liquid interface in a dilute binary alloy (1990)
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    Publication Date: 2011-08-19
    Description: This paper reconsiders the question of stability of a planar solid-liquid interface in an undercooled alloy melt without making the restrictive assumption of no heat flow in the solid (i.e., Gs = 0). The results of this analysis indicate that, provided the thermal gradient on the solid side of the interface, Gs, is positive, stability can be achieved in an undercooled alloy melt for growth rates R greater than Ra (where Ra is the absolute stability limit of Mullins and Sekerka, 1964). Thus, the absolute stability criterion for steady-state planar growth in an undercooled alloy melt is the same as derived earlier by Mullins and Sekerka for directional solidification. Relaxing the restrictive assumption of Gs = 0 also reveals that there is a regime of stability for low growth rates and low supercoolings.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Materials Research (ISSN 0884-2914); 5; 223-228
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    Numerical experiments in supersonic boundary-layer stability (1990)
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    Publication Date: 2011-08-19
    Description: The three-dimensional (3-D) time-dependent compressible Navier-Stokes equations are numerically solved by a Fourier-Chebyshev collocation method to study the stability of supersonic flows over a flat plate. Several direct simulations carried out in this study suggest the existence of a secondary instability that might provide a route to transition. The interaction of the modes involved in the secondary instability is possibly amenable to a Floquet-type analysis. Pertinent differences between this instability and the analogous incompressible K-type secondary instability are pointed out. Some preliminary results of a 2-D direct simulation of the nonlinear evolution of a second mode perturbation wave are also discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 94-104
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    On the three-dimensional instability of strained vortices (1990)
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    Publication Date: 2011-08-19
    Description: The three-dimensional (3-D) instability of a two-dimensional (2-D) flow with elliptical streamlines has been proposed as a generic mechanism for the breakdown of many 2-D flows. A physical interpretation for the mechanism is presented together with an analytical treatment of the problem. It is shown that the stability of an elliptical flow is governed by an Ince equation. An analytical representation for a localized solution is given and establishes a direct link with previous computations and experiments.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 76-80
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    Unsteady heat transfer on turbine blades (1990)
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    Publication Date: 2011-08-19
    Description: This paper describes a method for calculating heat transfer on turbine blades subjected to passing wakes. It is based on the numerical solution of the boundary-layer equations for laminar, transitional, and turbulent flows with a novel procedure to account for the movement of the stagnation point. Results are presented for a model flow and show that the procedure is numerically sound and produces results that can give good agreement with measurements provided that the turbulence model is adequate.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 4; 47-52
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    Two-dimensional convection and radiation with scattering from a Poiseuille flow (1990)
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    Publication Date: 2011-08-19
    Description: Two-dimensional combined convection and radiation heat transfer from a gray scattering fluid in a reflecting channel is considered. The model, represented by a set of simultaneous nonlinear integro-partial differential equations, is solved numerically. The effects of aspect ratio, conduction-radiation parameter, scattering albedo, and wall emissivity, are systematically investigated. It is found that these parameters have a significant influence on the temperature field and alter the radiative and convective fluxes at the hot and cold walls. In particular, when radiation effects are considerable, the heat-transfer characteristics of the fluid at the hot and cold walls are very different.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 4; 98-105
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    Elimination of spurious eigenvalues in the Chebyshev tau spectral method (1990)
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    Publication Date: 2011-08-19
    Description: A very simple modification is presented for the Chebyshev tau method which can eliminate spurious eigenvalues, proceeding from a consideration of the vorticity-streamfunction reformulation of the Chebyshev tau method and the Chebyshev-Galerkin method, which have no spurious modes. Consideration of a model problem indicates that these two approaches are equivalent, and that they reduce to the present modification of the tau method. This modified tau method also eliminates spurious eigenvalues from the Orr-Sommerfeld equation.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 91; 228-239
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    Stabilization of Taylor-Couette flow due to time-periodic outer cylinder oscillation (1990)
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    Publication Date: 2011-08-19
    Description: The linear stability of circular Couette flow between concentric infinite cylinders is considered for the case when the inner cylinder is rotated at a constant angular velocity and the outer cylinder is driven sinusoidally in time with zero mean rotation. This configuration was studied experimentally by Walsh and Donnelly. The critical Reynolds numbers calculated from linear stability theory agree well with the experimental values, except at large modulation amplitudes and small frequencies. The theoretical values are obtained using Floquet theory implemented in two distinct approaches: a truncated Fourier series representation in time, and a fundamental solution matrix based on a Chebyshev pseudospectral representation in space. For large amplitude, low frequency modulation, the linear eigenfunctions are temporally complex, consisting of a quiescent region followed by rapid change in the perturbed flow velocities.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 2147-215
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    The migration of a compound drop due to thermocapillarity (1990)
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    Publication Date: 2011-08-19
    Description: The quasistatic thermocapillary motion of a compound drop in an unbounded fluid possessing a uniform temperature gradient is analyzed. For completeness, gravitational effects are included in the treatment. The general model is formulated, and the equations for the concentric case are solved using spherical polar coordinates, while the eccentric case is handled using bispherical coordinates. Results are given for the velocity of the drop as well as that of the droplet with respect to the drop, along with useful approximations. Illustrative results are presented graphically for the thermocapillary migration of a compound drop in the special case when the droplet is a gas bubble. In addition to the velocities of the drop and the bubble, representative isotherms and streamlines also are presented which display interesting qualitative features.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 2119-213
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    Adaptive mesh generation for viscous flows using Delaunay triangulation (1990)
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    Publication Date: 2011-08-19
    Description: A method for generating an unstructured triangular mesh in two dimensions, suitable for computing high Reynolds number flows over arbitrary configurations is presented. The method is based on a Delaunay triangulation, which is performed in a locally stretched space, in order to obtain very high aspect ratio triangles in the boundary layer and the wake regions. It is shown how the method can be coupled with an unstructured Navier-Stokes solver to produce a solution adaptive mesh generation procedure for viscous flows.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 90; 271-291
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    A Poisson equation formulation for pressure calculations in penalty finite element models for viscous incompressible flows (1990)
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    Publication Date: 2011-08-19
    Description: The calculation of pressures when the penalty-function approximation is used in finite-element solutions of laminar incompressible flows is addressed. A Poisson equation for the pressure is formulated that involves third derivatives of the velocity field. The second derivatives appearing in the weak formulation of the Poisson equation are calculated from the C0 velocity approximation using a least-squares method. The present scheme is shown to be efficient, free of spurious oscillations, and accurate. Examples of applications are given and compared with results obtained using mixed formulations.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal for Numerical Methods in Engineering (ISSN 0029-5981); 30; 349-361
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    The baroeffect and an appropriate momentum boundary condition (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: As disparate molecular weight gases isothermally diffuse between two ends of a capillary tube, they can support a pressure gradient. The magnitude of this pressure gradient depends critically on viscous wall stress and becomes a measure of the boundary condition. Here, a one-dimensional analytical model is proposed that allows for specular gas reflection from the wall. It explains anomalous (4/3) correction factors required previously to match experiment to baroeffect models. It predicts a new physical phenomenon, a surface-driven baroeffect for equal molecular weight gases. Diffusive slip contributions exceed the order of convective diffusion for Peclet number Pe less than 1 and approximately equal convective diffusion for Pe values between 1 and 4. For binary gases, this model further extends the baroeffect experiment as a means to find momentum accommodation coefficients, slip lengths, and external friction coefficients. A corrected binary diffusion coefficient is defined.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 858-865
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    Effect of a crystal-melt interface on Taylor-vortex flow (1990)
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    Publication Date: 2011-08-19
    Description: The linear stability of circular Couette flow between concentric infinite cylinders is considered for the case that the stationary outer cylinder is a crystal-melt interface rather than a rigid surface. A radial temperature difference is maintained across the liquid gap, and equations for heat transport in the crystal and melt phases are included to extend the ordinary formulation of this problem. The stability of this two-phase system depends on the Prandtl number. For small Prandtl number the linear stability of the two-phase system is given by the classical results for a rigid-walled system. For increasing values of the Prandtl number, convective heat transport becomes significant and the system becomes increasingly less stable. Previous results in a narrow-gap approximation are extended to the case of a finite gap, and both axisymmetric and nonaxisymmetric disturbance modes are considered. The two-phase system becomes less stable as the finite gap tends to the narrow-gap limit. The two-phase system is more stable to nonaxisymmetric modes with azimuthal wavenumber n = 1; the stability of these n = 1 modes is sensitive to the latent heat of fusion.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 700-705
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    Hydrodynamic interactions in directional solidification (1990)
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    Publication Date: 2011-08-19
    Description: A binary liquid undergoes unidirectional solidification. The one-dimensional steady state is susceptible to morphological instability that causes the solid/liquid interface to change from a planar state to a cellular pattern. This paper examines the effects on this transition of volume-change convection, buoyancy-driven convection or forced flows. It emphasizes how flows alter stability limits, create scale and pattern changes in morphology, and create, through coupling, new instabilities. Emphasis is placed on the physical mechanisms of the interactions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 212; 241-262
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  • 66
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    Preliminary drop-tower experiments on liquid-interface geometry in partially filled containers at zero gravity (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Plexiglass containers with rounded trapezoidal cross sections were designed and built to test the validity of Concus and Finn's existence theorem (1974, 1983) for a bounded free liquid surface at zero gravity. Experiments were carried out at the NASA Lewis two-second drop tower. Dyed ethanol-water solutions and three immiscible liquid pairs, with one liquid dyed, were tested. High-speed movies were used to record the liquid motion. Liquid rose to the top of the smaller end of the containers when the contact angle was small enough, in agreement with the theory. Liquid interface motion demonstrated a strong dependence on physical properties, including surface roughness and contamination.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Experiments in Fluids (ISSN 0723-4864); 8; 6, Ma; 312-318
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    A contribution toward rational modeling of the pressure-strain-rate correlation (1990)
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    Publication Date: 2011-08-19
    Description: A novel method of obtaining an analytical expression of the 'linear part' of the pressure-strain-rate tensor in terms of the anisotropy tensor of the Reynolds stresses has been developed, where the coefficients of the seven independent tensor terms are functions of the invariants of the Reynolds-stress anisotropy. The coefficients are evaluated up to fourth order in the anisotropy of the Reynolds stresses to provide guidance for development of a turbulence model.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 630-633
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    Control of turbulent separated flow over a rearward-facing ramp using longitudinal grooves (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Aircraft (ISSN 0021-8669); 27; 283-285
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  • 69
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    Rotational-translational energy transfer in rarefied nonequilibrium flows (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A new model for simulating the transfer of energy between the translational and rotational modes is derived for a homogeneous gas of diatomic molecules. The model has been developed specifically for use in discrete particle simulation methods where molecular motion and intermolecular collisions are treated at the molecular level. A temperature dependence is introduced which has been predicted by theory and observed in experiment. The new model is applied to the relaxation of rotational temperature, and is found to produce significant differences in comparison with the model normally employed at both high and low temperatures. Calculations have also been performed for a Mach 7 normal shock wave.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 447-452
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    Parallel flows with Soret effect in tilted cylinders (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Henry and Roux (1986, 1987, 1988) have conducted extensive numerical studies on the interaction of Soret separation with convection in cylindrical geometry. Many of their solutions exhibit parallel flow away from end walls. Their parallel flow results can be matched by closed-form solutions. Solutions are nonunique in some parameter regions. Disappearance of one branch of solutions correlates with a sudden transition of Henry and Roux's results from a separated to a well-mixed flow.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 211; 355-372
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    Theoretical study of turbulent channel flow - Bulk properties, pressure fluctuations, and propagation of electromagnetic waves (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In this paper, we apply two theoretical turbulence models, DIA and the recent GISS model, to study properties of a turbulent channel flow. Both models provide a turbulent kinetic energy spectral function E(k) as the solution of a non-linear equation; the two models employ the same source function but different closures. The source function is characterized by a rate n sub s (k) which is derived from the complex eigenvalues of the Orr-Sommerfeld (OS) equation in which the basic flow is taken to be of a Poiseuille type. The O-S equation is solved for a variety of Reynolds numbers corresponding to available experimental data. A physical argument is presented whereby the central line velocity characterizing the basic flow, U0 sup L, is not to be identified with the U0 appearing in the experimental Reynolds number. The theoretical results are compared with two types of experimental data: (1) turbulence bulk properties, and (2) properties that depend strongly on the structure of the turbulence spectrum at low wave numbers. The only existing analytical expression for Pi (k) cannot be used in the present case because it applies to the case of a flat plate, not a finite channel.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 211; 1-35
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    Splitting of inviscid fluxes for real gases (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Flux-vector and flux-difference splittings for the inviscid terms of the compressible flow equations are derived under the assumption of a general equation of state for a real gas in equilibrium. No necessary assumptions, approximations for auxiliary quantities are introduced. The formulas derived include several particular cases known for ideal gases and readily apply to curvilinear coordinates. Applications of the formulas in a TVD algorithm to one-dimensional shock-tube and nozzle problems show their quality and robustness.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 87; 1-24
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    Improvement of pump tubes for gas guns and shock tube drivers (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In a pump tube, a gas is mechanically compressed, producing very high pressures and sound speeds. The intensely heated gas produced in such a tube can be used to drive light gas guns and shock tubes. Three concepts are presented that have the potential to allow substantial reductions in the size and mass of the pump tube to be achieved. The first concept involves the use of one or more diaphragms in the pump tube, thus replacing a single compression process by multiple, successive compressions. The second concept involves a radical reduction in the length-to-diameter ratio of the pump tube and the pump tube piston. The third concept involves shock heating of the working gas by high explosives in a cyclindrical geometry reusable device. Preliminary design analyses are performed on all three concepts and they appear to be quite feasible. Reductions in the length and mass of the pump tube by factors up to about 11 and about 7, respectively, are predicted, relative to a benchmark conventional pump tube.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 28; 483-491
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    Separated flow upstream of a jet in a crossflow (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 28; 414-420
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    Wave formation on a liquid layer for de-icing airplane wings (1990)
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    Publication Date: 2011-08-19
    Description: Wave formation on a thin liquid layer used for deicing aircraft wings is investigated by studying the stability of airflow over a liquid-coated flat plate at zero angle of incidence. The ratio of the viscosity of the liquid to that of air is very high (over 500,000), and the Reynolds number based on liquid depth and air viscosity is of the order of a few thousand. Under these circumstances the analysis gives two formulas, in closed form, for the growth rate and phase velocity of the waves in terms of the wavenumber and other relevant parameters. The expected wavenumber is that for which the growth rate is the maximum. The instability is one in which the viscosity difference between the two fluids (air and liquid) plays the dominant role, and is of the kind found by Yih (1967).
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 212; 41-53
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    Buoyancy-driven instability in a vertical cylinder: Binary fluids with Soret effect. I - General theory and stationary stability results (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The buoyancy-driven instability of a monocomponent or binary fluid completely contained in a vertical circular cylinder is investigated, including the influence of the Soret effect for the binary mixture. The Boussinesq approximation is used, and the resulting linear stability problem is solved using a Galerkin technique. The analysis considers fluid mixtures ranging from gases to liquid metals. The flow structure is found to depend strongly on both the cylinder aspect ratio and the magnitude of the Soret effect. The predicted stability limits are shown to agree closely with experimental observations.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal for Numerical Methods in Fluids (ISSN 0271-2091); 10; 79-117
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    Calculation of shocked one-dimensional flows on abruptly changing grids by mathematical programming (1990)
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    Publication Date: 2011-08-19
    Description: Cell-centered finite differences on cells of an arbitrarily spaced grid are presently used to discretize the steady-state inviscid and nearly inviscid Burgers' equations for steady-state shocked flow in a quasi-one-dimensional nozzle. The everdetermined system of nonlinear algebraic equations thus obtained is solved by a procedure which minimizes a weighted sum of the residuals' absolute values. Numerical solutions for both viscous and inviscid problems are accurate and nonoscillatory, on grids whose abrupt mesh lengths refinements are as great as a factor of 10,000.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 86; 1-17
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    Emittance bounds for transient radiative cooling of a scattering rectangular region (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Transient cooling was analyzed for a two-dimensional gray rectangular region that emits, absorbs, and isotropically scatters radiation. The region, initially at uniform temperature, is placed in surroundings at a much lower temperature. The cooling analysis yields two simultaneous equations for the transient temperature and scattering source function distributions. The region starts to cool with the medium at uniform temperature. For this condition, the local emittance around the perimeter was obtained by a numerical solution of the radiative equations, and the rate of heat loss from the entire medium was evaluated. As cooling continues, the emissive ability decreases because of the lower temperatures in the outer regions of the rectangle. Based on some previous work, a lower limit for the transient overall emittance was found by obtaining a similarity solution. For some ranges of optical thickness and scattering albedo, the lower limit is only a small amount below the initial emittance. For these conditions, the initial emittance can be used to compute the entire transient resulting in a considerable simplification.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 4; 106-114
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    A Detailed Investigation of Staged Normal Injection into a Mach 2 Flow (1990)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: A study of the staged injection of two jets of air behind a rearward facing step into a Mach 2 flow was performed using the SPARK 3-D Navier-Stokes code. Calculated mole fraction distributions were compared with an extensive set of planar mole fraction measurements made with a laser induced iodine fluorescence technique. A statistical measure, the standard deviation, was used to help assess agreement between calculation and experiment. Overall, good agreement was found between calculated and measured values. Generally, agreement was better in the far field of the injectors. The effect of grid resolution was investigated by calculating solutions on grids of 60,000, 200,000, and 450,000 points. Differences in the solutions on the two finer grids were small. However, the mole fraction distributions were distinguishable. The effect of turbulence modeling was investigated by employing three different algebraic models for the jet turbulence: the Baldwin-Lomax model, the Prandtl mixing length model, and the Eggers mixing length model. Overall, the Eggers mixing length model was found to be superior for this case. Finally, the effect of the jet exit conditions was examined. A recently proposed Mach number distribution at the jet exit was found to slightly improve agreement between measurement and calculation.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: 27th JANNAF Combustion Subcommittee Meeting; Volume 3; 115-129
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    Tailoring explicit time-marching schemes to improve convergence characteristics (1990)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Multi-stage time-stepping schemes, tailored to chosen spatial-differencing operators, are derived and tested. The schemes are constructed to give optimal damping of the high-frequency waves. They are ideal for use with multi-grid acceleration. The concept of characteristic time-stepping, necessary for the extension of the scalar analysis to systems of equations, is presented. The schemes show a marked improvement over Runge-Kutta schemes.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: VKI, Computational Fluid Dynamics, Volume 2; 30 p
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    Towards a genuinely multi-dimensional upwind scheme (1990)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Methods of incorporating multi-dimensional ideas into algorithms for the solution of Euler equations are presented. Three schemes are developed and tested: a scheme based on a downwind distribution, a scheme based on a rotated Riemann solver and a scheme based on a generalized Riemann solver. The schemes show an improvement over first-order, grid-aligned upwind schemes, but the higher-order performance is less impressive. An outlook for the future of multi-dimensional upwind schemes is given.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: VKI, Computational Fluid Dynamics, Volume 2; 55 p
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    On unstructured grids and solvers (1990)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The fundamentals and the state-of-the-art technology for unstructured grids and solvers are highlighted. Algorithms and techniques pertinent to mesh generation are discussed. It is shown that grid generation and grid manipulation schemes rely on fast multidimensional searching. Flow solution techniques for the Euler equations, which can be derived from the integral form of the equations are discussed. Sample calculations are also provided.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: VKI, Computational Fluid Dynamics, Volume 2; 66 p
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  • 83
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    High-speed inlet research program and supporting analysis (1990)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The technology challenges faced by the high speed inlet designer are discussed by describing the considerations that went into the design of the Mach 5 research inlet. It is shown that the emerging three dimensional viscous computational fluid dynamics (CFD) flow codes, together with small scale experiments, can be used to guide larger scale full inlet systems research. Then, in turn, the results of the large scale research, if properly instrumented, can be used to validate or at least to calibrate the CFD codes.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Aeropropulsion 1987; p 469-486
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    Chemical reacting flows (1990)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Future aerospace propulsion concepts involve the combustion of liquid or gaseous fuels in a highly turbulent internal airstream. Accurate predictive computer codes which can simulate the fluid mechanics, chemistry, and turbulence-combustion interaction of these chemical reacting flows will be a new tool that is needed in the design of these future propulsion concepts. Experimental and code development research is being performed at LeRC to better understand chemical reacting flows with the long-term goal of establishing these reliable computer codes. Our approach to understand chemical reacting flows is to look at separate, more simple parts of this complex phenomenon as well as to study the full turbulent reacting flow process. As a result, we are engaged in research on the fluid mechanics associated with chemical reacting flows. We are also studying the chemistry of fuel-air combustion. Finally, we are investigating the phenomenon of turbulence-combustion interaction. Research, both experimental and analytical, is highlighted in each of these three major areas.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Aeropropulsion 1987; p 197-208
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    Inlets, ducts, and nozzles (1990)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The internal fluid mechanics research program in inlets, ducts, and nozzles consists of a balanced effort between the development of computational tools (both parabolized Navier-Stokes and full Navier-Stokes) and the conduct of experimental research. The experiments are designed to better understand the fluid flow physics, to develop new or improved flow models, and to provide benchmark quality data sets for validation of the computational methods. The inlet, duct, and nozzle research program is described according to three major classifications of flow phenomena: (1) highly 3-D flow fields; (2) shock-boundary-layer interactions; and (3) shear layer control. Specific examples of current and future elements of the research program are described for each of these phenomenon. In particular, the highly 3-D flow field phenomenon is highlighted by describing the computational and experimental research program in transition ducts having a round-to-rectangular area variation. In the case of shock-boundary-layer interactions, the specific details of research for normal shock-boundary-layer interactions are described. For shear layer control, research in vortex generators and the use of aerodynamic excitation for enhancement of the jet mixing process are described.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Aeropropulsion 1987; p 157-174
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    On the Subgrid-Scale Modeling of Compressible Turbulence (1990)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: A new sub-grid scale model is presented for the large-eddy simulation of compressible turbulence. In the proposed model, compressibility contributions have been incorporated in the sub-grid scale eddy viscosity which, in the incompressible limit, reduce to a form originally proposed by Smagorinsky (1963). The model has been tested against a simple extension of the traditional Smagorinsky eddy viscosity model using simulations of decaying, compressible homogeneous turbulence. Simulation results show that the proposed model provides greater dissipation of the compressive modes of the resolved-scale velocity field than does the Smagorinsky eddy viscosity model. For an initial r.m.s. turbulence Mach number of 1.0, simulations performed using the Smagorinsky model become physically unrealizable (i.e., negative energies) because of the inability of the model to sufficiently dissipate fluctuations due to resolved scale velocity dilations. The proposed model is able to provide the necessary dissipation of this energy and maintain the realizability of the flow. Following Zeman (1990), turbulent shocklets are considered to dissipate energy independent of the Kolmogorov energy cascade. A possible parameterization of dissipation by turbulent shocklets for Large-Eddy Simulation is also presented.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Studying Turbulence Using Numerical Simulation Databases. 3: Proceedings of the 1990 Summer Program; p 47-59
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    Correlation of leak rates of various fluids with the leak rate of an inert gas in the same configuration (1990)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: NASA is interested in field testing for possible leakage in their fueling systems; however, many fuels are hazardous to the extent that personnel cannot be on hand when the system is being monitored. It is proposed that an inert material such as helium be used on the field test, and that those results be calibrated to simulate the actual process. A technique such as this would allow personnel to be on site during the testing and use techniques to determine the behavior of the system that could not be used otherwise. This endeavor attempts to develop such a correlation. The results show promise, but more refinement and data are needed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA, John F. Kennedy Space Center, Research Reports: 1990 NASA(ASEE Summer Faculty Fellowship Program; p 308-338
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    Flow fields of low pressure vent exhausts (1990)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The flow field produced by low pressure gas vents are described based on experimental data obtained from tests in a large vacuum chamber. The gas density, pressure, and flux at any location in the flow field are calculated based on the vent plume description and the knowledge of the flow rate and velocity of the venting gas. The same parameters and the column densities along a specified line of sight traversing the plume are also obtained and shown by a computer generated graphical representation. The fields obtained with a radically scanning Pitot probe within the exhausting gas are described by a power of the cosine function, the mass rate, and the distance from the exit port. The field measurements were made for gas at pressures ranging from 2 to 50 torr venting from pipe fittings with diameters to 3/16 to 1-1/2 inches I.D. (4.76 to 38.1 mm). The N2 mass flow rates ranged from 2E-4 to 3.7E-1 g/s.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: 16th Space Simulation Conference Confirming Spaceworthiness Into the Next Millennium; p 75-83
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    Surface Reorientation and Settling in Cylinders upon Step Reduction in Gravity (1990)
    In:  Other Sources
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    Publication Date: 2013-08-22
    Description: A large literature exists concerning the equilibrium configurations of free liquid/gas surfaces in reduced gravity environments. Such conditions generally yield surfaces of constant curvature contracting the container wall at a particular angle. The time required to reach and stabilize about this configuration is less studied for the case of sudden changes in gravity level; e.g., from normal- to low-gravity, as can occur in many drop tower experiments. The particular interest here was to determine the total reorientation time for such surfaces in cylinders, as a function primarily of contact angle and kinematic viscosity, in order to aid in the development of drop tower experiment design. A large parametric range of tests were performed and, based on an accompanying scale analysis, the complete data set was correlated. The results of other investigations are included for comparison.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Microgravity Science and Technology (ISSN 0938-0108); 3; 24-32
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  • 90
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    Generation of large-scale density fluctuations by buoyancy (1990)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: The generation of fluid motion from a state of rest by buoyancy forces acting on a homogeneous isotropic small-scale density field is considered. Nonlinear interactions between the generated fluid motion and the initial isotropic small-scale density field are found to create an anisotropic large-scale density field with spectrum proportional to kappa(exp 4). This large-scale density field is observed to result in an increasing Reynolds number of the fluid turbulence in its final period of decay.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Stanford Univ., Studying Turbulence Using Numerical Simulation Databases. 3: Proceedings of the 1990 Summer Program; p 313-318
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  • 91
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    Transition to turbulence in hypersonic flow (1990)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: An outline of the project and recent progress toward the study of transition in hypersonic boundary layers is given. Aspects of the numerical method and the results of test computations are presented. At present the laminar flows over a flat plate have been computed for M less than or equal to 5.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Annual Research Briefs, 1989; p 157-168
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  • 92
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    Short-time Lyapunov exponent analysis (1990)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: A new technique for analyzing complicated fluid flows in numerical simulations has been successfully tested. The analysis uses short time Lyapunov exponent contributions and the associated Lyapunov perturbation fields. A direct simulation of the Taylor-Couette flow just past the onset of chaos demonstrated that this new technique marks important times during the system evolution and identifies the important flow features at those times. This new technique will now be applied to a 'minimal' turbulent channel.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Annual Research Briefs, 1989; p 97-106
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  • 93
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    Organized motions underlying turbulent shear flows (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: The objective of this project is to determine the nature and significance of the organized motions underlying turbulent shear flow. There is considerable experimental evidence for the existence of such motions. In particular, one consistently observes longitudinal streaks with a spacing of about 100 in wall units in the near-wall region of wall-bounded shear flows. Recently, an analysis based on the direct resonance mechanism has predicted the appearance of streaks with precisely such a spacing. Also, the minimum channel simulations of Jimenez and Moin have given a strong dynamical significance to that spanwise length scale. They have shown that turbulent-like flows can not be maintained when the spanwise wavelength of the motion is constrained to be less than about that critical number. A critical review of the direct resonance ideas and the non-linear theory of Benney and Gustavsson is presented first. It is shown how this leads to the later mean flow-first harmonic theory of Benney. Finally, we note that a different type of analysis has led to the prediction streaks with a similar spacing. This latter approach consists of looking for optimum fields and directly provides deep insights into why a particular structure or a particular scale should be preferred.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Annual Research Briefs, 1989; p 107-115
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  • 94
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    An experimental study of the effects of rapid rotation on turbulence (1990)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: Experiments, large eddy simulations and direct numerical simulations all show that rapid rotation has a striking effect on homogeneous nearly isotropic turbulence. The cascade process is effectively inhibited by rotation, and thus dissipation is greatly reduced. Some attempts have been made to incorporate this effect in turbulence models. Numerical simulation further showed the somewhat surprising result that anisotropic homogeneous turbulence subjected to rotation tended towards an isotropic state; however, the residual anisotropy was not zero. Reynolds (1989) performed a detailed analysis using Rapid Distortion Theory (RDT) and showed that a reduction in the anisotropy is indeed expected and if the anisotropy is produced by irrotational strain then the anisotropy tensor b(sub ij) is asymptotically driven to half its initial value. Our objective is to extend the work of the experiments mentioned above to lower turbulent Rossby numbers and to confirm some of the results obtained by Reynolds (1989) for anisotropic turbulence.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Annual Research Briefs, 1989; p 51-57
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  • 95
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    A fractal transition in the two dimensional shear layer (1990)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: The dependence of product generation with the Peclet and Reynolds number in a numerically simulated, reacting, two dimensional, temporally growing mixing layer is used to compute the fractal dimension of passive scalar interfaces. A transition from a low dimension of 4/3 to a higher one of 5/3 is identified and shown to be associated to the kinematic distortion on the flow field during the first pairing interaction. It is suggested that the structures responsible for this transition are non-deterministic, non-random, inhomogeneous fractals. Only the large scales are involved. No further transition is found for Reynolds numbers up to 20,000.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Studying Turbulence Using Numerical Simulation Databases. 3: Proceedings of the 1990 Summer Program; p 235-242
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  • 96
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    Resonant instability of supersonic shear layers (1990)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: A computer simulation of possible resonant instability of a supersonic shear layer is carried out. The resonance of two acoustic duct modes of the flow induced by periodic Mach waves generated by a wavy wall is sought. Results of the simulations are reported. Simulations are unable to document a resonant instability and the mixing characteristics remain unchanged. Possible weakness of the present simulations are discussed. A second set of simulations involving a mixing layer separating a supersonic and a subsonic stream were performed. A wavy wall placed adjacent to the supersonic stream to produce a set of periodic Mach waves terminating at the shear layer is modelled. The entire flow field is similar to that of an imperfectly expanded supersonic jet discharging into a subsonic coflowing stream for which enhanced mixing due to the onset of screech (feedback instability) is known to occur. The purpose of these simulations is to see if enhanced mixing and feedback instability would, indeed, take place. Some evidence of feedback oscillations is found in the simulated flow.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Stanford Univ., Studying Turbulence Using Numerical Simulation Databases. 3: Proceedings of the 1990 Summer Program; p 191-201
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  • 97
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    Low Reynolds number kappa-epsilon modeling with the aid of direct simulation data (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: The constant C(sub mu) and the near-wall damping function f(sub mu) in the eddy-viscosity relation of the kappa-epsilon model are evaluated from direct numerical simulation (DNS) data for developed channel and boundary layer flow at two Reynolds numbers each. Various existing f(sub mu) model functions are compared with the DNS data, and a new function is fitted to the high-Reynolds-number channel flow data. The epsilon-budget is computed for the fully developed channel flow. The relative magnitude of the terms in the epsilon-equation is analyzed with the aid of scaling arguments, and the parameter governing this magnitude is established. Models for the sum of all source and sink terms in the epsilon-equation are tested against the DNS data, and an improved model is proposed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Stanford Univ., Studying Turbulence Using Numerical Simulation Databases. 3: Proceedings of the 1990 Summer Program; p 85-106
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  • 98
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    A subgrid-scale model based on the second-order velocity structure function (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: A series of tests were performed to help extend the use of a subgrid-scale model to compressible and wall-bounded flows. A priori tests were done in the case of the incompressible turbulent channel flow. They showed that a 1-D formulation of the structure-function model is more appropriate, leading to a satisfactory behavior of the model at the walls without requiring any damping function. This model is consistent with the original formulation of Metais & Lesieur (1990). In large-eddy simulations of compressible isotropic turbulence, both models performed well up to an initial rms Mach number of 0.6.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Stanford Univ., Studying Turbulence Using Numerical Simulation Databases. 3: Proceedings of the 1990 Summer Program; p 31-45
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  • 99
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    A numerical method for prediction of compressible turbulent flows with closure models (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: A new computer code to solve the time averaged Navier-Stokes equations is developed. Many of the state-of-the-art numerical techniques and algorithms have been tested and implemented in the program in order to achieve a better numerical accuracy and code efficiency. Various turbulence models are tested for a wide range of flows. The initial focus has been on two-equation eddy-viscosity models, which are the most advanced available in current compressible flow codes. The long term goal will be to test Reynolds-Stress models and to explore their performance in the high Mach number range. Although testing and improvement of turbulence models for supersonic and hypersonic flows is the primary objective of this research, part of the effort has been devoted to analyzing the vortex breakdown phenomena using new computer programs. Some preliminary results on the breakdown of a vortex flow in a tube are reported. Present calculations are restricted to two dimensional flow geometry.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Annual Research Briefs, 1989; p 185-193
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  • 100
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    Modeling of compressible turbulence (1990)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: The work is directed toward understanding and modeling compressibility effects in turbulent flows. The primary objective is to investigate how compressibility influences the basic turbulence processes such as turbulence production and dissipation, length scale modification, spectral energy transfer, etc. The second objective is to develop parameterization schemes and models to incorporate compressibility into one-point closure models and into the subgrid scale models for LES techniques. The ultimate purpose of this research is to develop compressible turbulence models which are capable of handling the hypersonic regime. Specifically, the emphasis will be on the model capability of predicting: (1) heat and momentum transfer in hypersonic boundary layers; and (2) mixing and growth of high Mach number shear layers, jet and wakes.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Annual Research Briefs, 1989; p 3-12
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