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  • Life and Medical Sciences  (1,825)
  • FLUID MECHANICS AND HEAT TRANSFER  (731)
  • Engineering  (662)
  • 1990-1994  (3,218)
  • 1993  (3,218)
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  • 1990-1994  (3,218)
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  • 1
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    Multiple solutions in a rotating annulus flow model (1993)
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    Publication Date: 2019-08-28
    Description: A series of numerical experiments is conducted for rotating annulus flow using Miller et al.'s (1992) Geophysical Flow Simulation (GFS) model; a mixture of 25-percent upwind-differencing and 75-percent center-differencing is employed to approximate the temperature advective terms. Attention is given to the wavenumber selection time and wavenumber regimes, the sensitivity in the wavenumber transition regions, and hysteresis and irregular wavenumber selections.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: ; : Micro(
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  • 2
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    Navier-Stokes relaxation to sinh-Poisson states at finite Reynolds numbers (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: A mathematical framework is proposed in which it seems possible to justify the computationally-observed relaxation of a two-dimensional Navier-Stokes fluid to a 'most probable', or maximum entropy, state. The relaxation occurs at large but finite Reynolds numbers, and involves substantial decay of higher-order ideal invariants such as enstrophy. A two-fluid formulation, involving interpenetrating positive and negative vorticity fluxes (continuous and square integrable) is developed, and is shown to be intimately related to the passive scalar decay problem. Increasing interpenetration of the two fluids corresponds to the decay of vorticity flux due to viscosity. It is demonstrated numerically that, in two dimensions, passive scalars decay rapidly, relative to mean-square vorticity (enstrophy). This observation provides a basis for assigning initial data to the two-fluid field variables.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 5; 9; p. 2207-2216.
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  • 3
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    New two-temperature dissociation model for reacting flows (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 7; 4; p. 687-696.
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  • 4
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    Direct simulation with vibration-dissociation coupling (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 7; 4; p. 680-686.
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  • 5
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    Steady, three-dimensional, internally heated convection (1993)
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    Publication Date: 2019-08-28
    Description: Numerical calculations have been carried out of steady, symmetric, 3D modes of convection in internally heated, infinite Prandtl number, Boussinesq fluids at a Rayleigh number of 1.4 x 10 exp 4 in a spherical shell with inner/outer radius of 0.55 and in a 3 x 3 x 1 rectangular box. Multiple patterns of convection occur in both geometries. In the Cartesian geometry, the patterns are dominated by cylindrical cold downflows and a broad hot upwelling. In the spherical geometry the patterns consist of cylindrical cold downwellings centered either at the vertices of a tetrahedron or the centers of the faces of a cube. The cold downflow cylinders are immersed in a background of upwelling within which there are cylindrical hot concentrations (plumes) and hot halos around the downflows. The forced hot upflow return plumes of internally heated spherical convection are fundamentally different from the buoyancy-driven plumes of heated from below convection.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 5; 8; p. 1928-1932.
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  • 6
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    Singularities in the classical Rayleigh-Taylor flow - Formation and subsequent motion (1993)
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    Publication Date: 2019-08-28
    Description: The creation and subsequent motion of singularities of solution to classical Rayleigh-Taylor flow (two dimensional inviscid, incompressible fluid over a vacuum) are discussed. For a specific set of initial conditions, we give analytical evidence to suggest the instantaneous formation of one or more singularities at specific points in the unphysical plane, whose locations depend sensitively on small changes in initial conditions in the physical domain. One-half power singularities are created in accordance with an earlier conjecture; however, depending on initial conditions, other forms of singularities are also possible. For a specific initial condition, we follow a numerical procedure in the unphysical plane to compute the motion of a one-half singularity. This computation confirms our previous conjecture that the approach of a one-half singularity towards the physical domain corresponds to the development of a spike at the physical interface. Under some assumptions that appear to be consistent with numerical calculations, we present analytical evidence to suggest that a singularity of the one-half type cannot impinge the physical domain in finite time.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Royal Society (London), Proceedings, Series A - Mathematical and Physical Sciences (ISSN 0962-8444); 441; 1913; p. 501-525.
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  • 7
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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
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    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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  • 8
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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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  • 9
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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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  • 10
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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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