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  • Life and Medical Sciences  (10,247)
  • FLUID MECHANICS AND HEAT TRANSFER  (4,418)
  • 1990-1994  (11,693)
  • 1975-1979  (2,972)
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  • 11
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    A novel pulse technique for thermal diffusivity determination of high-temperature levitated materials - Inverse analysis and experimental set-up (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: In order to determine the thermal diffusivity of materials at high temperatures, a two-step extended flash technique, which is applicable to levitated spherical samples, is proposed. The containerless flash method is modeled as an axisymmetric transient conduction heat transfer problem within the sphere subjected to a radiative boundary condition on its surface. The problem of nonlinearity which arises from the radiative heat transfer boundary condition is solved by replacing it with the measured time-dependent surface temperature data, thus giving rise to an 'Inverse Analysis'. Upon obtaining the analytic solution for the temperature field, the determination of the thermal diffusivity turns into a minimization problem, whereby the difference between the actual surface boundary condition and the analytic solution is minimized. In performing the proposed experiments, there is a need to undertake a cool-down experiment which should be governed by the lumped parameter analysis.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 93-2756 , ; 7 p.|AIAA, Thermophysics Conference; Jul 06, 1993 - Jul 09, 1993; Orlando, FL; United States
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  • 12
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    Finite-element solution scheme for compressible viscous flow (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Adaptivity offers the possibility of using FEM for problems that are otherwise intractable. The solution algorithm is combined with an adaptive approach in which the unstructured portion of the grid is adaptively regenerated as the solution proceeds; the structured portion of the mesh is modified accordingly, to ensure both compatibility along the interface between the implicit and explicit element groups and increased resolution of the viscous layer. The approach offers significant computational savings in 3D simulations.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: In: Finite elements in fluids. Vol. 8 (A93-45962 19-34); p. 47-73.
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  • 13
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    On the dynamical buoyancy of vortices (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: In this paper we consider the effect of dynamical buoyancy (Parker) on the motion of stratified fluid vortex tubes. We find that the dynamical buoyancy force does not necessarily lead to a buoyant rise if there exists a flow field external to a tube. In particular, the vortex tubes presented in our previous work are shown to have a pressure force exactly canceling the buoyancy force so that they do not move vertically (i.e., parallel to gravity) at all. Moreover, we construct a more general class of vortex tubes and find that their vertical motion can be either up or down, depending on the detailed vorticity distribution, regardless of the fact that they are all dynamically buoyant. We find that the vertical motion is intimately related to the horizontal self-motion of stratified fluid vortex tubes. Finally, we note that the presence of dynamical buoyancy implies that steady state compressible flow solutions for isolated fluid regions in a gravitational field do not exist. These results may have relevance to astrophysical convection.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 412; 2; p. 664-674.
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  • 14
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    An implicit method for two-dimensional hydrodynamics (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: An implicit method for compressible multidimensional flows is presented. The method, which is strongly oriented toward astrophysical applications, enables one to simulate very subsonic flows by removing the Courant condition upon time steps. It consists of an implicit purely Lagrangian step, followed by an explicit and second-order accurate (at least in one dimension) remapping step, which is optional. When the remapping step is performed the time step is limited by the 'particle crossing time' and otherwise it is limited only by accuracy considerations. The suggested method, which results from a compromise between accuracy and efficiency, is very efficient relative to other methods. It enables the computation of many multidimensional problems in stellar evolution, such as those governed by very subsonic flows, which were not calculable with existing explicit methods.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 412; 2; p. 634-647.
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  • 15
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    DSMC simulation of low Reynolds number nozzle flows (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: A numerical analysis of low Reynolds number nozzle flows was performed to investigate the loss mechanisms involved and to determine the nozzle wall contour that minimizes these losses. DSMC was used to simulate flows through three different nozzle configurations at two different stagnation chamber temperatures so that the heat transfer losses could be separated from the wall contour effects on performance. A trumpet-shaped nozzle had 5 percent higher efficiency than a conical nozzle and a 3 percent higher efficiency than a bell-shaped nozzle with the unheated flow. With heated flow both the trumpet and bell-shaped nozzles had a 6.5 percent higher efficiency than the conical nozzle. The conical nozzle had the highest discharge coefficient of the three configurations, 0.92, and the trumpet-shaped nozzle had the lowest, 0.82. The discharge coefficient of each nozzle was unaffected by the change in stagnation temperature; however the increase in stagnation temperature increased the heat transfer and viscous losses in the boundary layer. These results suggest that the trumpet-shaped wall contour performed most efficiently except near the throat region, where it incurred large viscous losses. However, the bell-shaped nozzle may increase its overall performance with an increase in stagnation temperature.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 93-2490 , ; 24 p.|AIAA, SAE, ASME, and ASEE, Joint Propulsion Conference and Exhibit; Jun 28, 1993 - Jun 30, 1993; Monterey, CA; United States
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  • 16
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    Modeling of turbulent supersonic H2-air combustion with a multivariate beta PDF (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Recent calculations of turbulent supersonic reacting shear flows using an assumed multivariate beta PDF (probability density function) resulted in reduced production rates and a delay in the onset of combustion. This result is not consistent with available measurements. The present research explores two possible reasons for this behavior: use of PDF's that do not yield Favre averaged quantities, and the gradient diffusion assumption. A new multivariate beta PDF involving species densities is introduced which makes it possible to compute Favre averaged mass fractions. However, using this PDF did not improve comparisons with experiment. A countergradient diffusion model is then introduced. Preliminary calculations suggest this to be the cause of the discrepancy.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 93-2198 , AIAA, SAE, ASME, and ASEE, Joint Propulsion Conference and Exhibit; Jun 28, 1993 - Jun 30, 1993; Monterey, CA; United States|; 13 p.
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  • 17
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    Steady flow on to a conveyor belt - Causal viscosity and shear shocks (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Some hydrodynamical consequences of the adoption of a causal theory of viscosity are explored. Causality is introduced into the theory by letting the coefficient of viscosity go to zero as the flow velocity approaches a designated propagation speed for viscous signals. Consideration is given to a model of viscosity which has a finite propagation speed of shear information, and it is shown that it produces two kinds of shear shock. A 'pure shear shock' corresponds to a transition from a superviscous to a subviscous state with no discontinuity in the velocity. A 'mixed shear shock' has a shear transition occurring at the same location as a normal adiabatic or radiative shock. A generalized version of the Rankine-Hugoniot conditions for mixed shear shocks is derived, and self-consistent numerical solutions to a model 2D problem in which an axisymmetric radially infalling stream encounters a spinning star are presented.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 262; 3; p. 749-763.
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  • 18
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    Boundary layer energization by means of optimized vortex generators (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: A three-dimensional, multi-block, multi-zone, Euler analysis has been developed and applied to analyze the flow processes induced by a lateral array of low profile vortex generators (VG). These vortex generators have been shown to alleviate boundary layer separation through the generation of streamwise vorticity. The analysis has been applied to help develop improved VG configurations in an efficient manner. Special attention has been paid to determining the accuracy requirements of the solver for calculations in which vortical mechanisms are dominant. The analysis has been used to assess the effectiveness or boundary layer energization capacity of different VG's, including the effect of scale and shape variation. Finally, the analysis has been validated through comparisons with experimental data obtained in a large-scale low-speed wind tunnel.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 93-0445 , AIAA, Aerospace Sciences Meeting and Exhibit; Jan 11, 1993 - Jan 14, 1993; Reno, NV; United States|; 11 p.
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  • 19
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    Modeling and computation of turbulent free-surface jets (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: A 2D numerical model for a turbulent surface jet issuing into a finite-depth channel is presented. The model uses an unstructured, finite element procedure. The calculations confirm the experimental observation that scale similarity may be apparent in the mean velocity profile even in the presence of a large encroaching recirculation cell.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 93-0201 , ; 11 p.|AIAA, Aerospace Sciences Meeting and Exhibit; Jan 11, 1993 - Jan 14, 1993; Reno, NV; United States
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  • 20
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    A fully nonlinear, mixed spectral and finite difference model for thermally driven, rotating flows (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Finite difference in time and the meridional plane, in conjunction with a spectral technique in the azimuthal direction, are used to approximate the Navier-Stokes equations in a model that can simulate a variety of thermally driven rotating flows in cylindrical and spherical geometries. Axisymmetric flow, linearized waves relative to a fixed or changing axisymmetric flow, nonlinear waves without wave-wave interaction, and fully nonlinear 3D flow, can in this way be calculated. A reexamination is conducted of the steady baroclinic wave case previously treated by Williams (1971) and Quon (1976).
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 101; 2, Au; 265-275
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