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  • FLUID MECHANICS AND HEAT TRANSFER  (6)
  • 2020-2022
  • 2015-2019
  • 2005-2009
  • 1990-1994  (6)
  • 1970-1974
  • 1993  (6)
  • 1
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    On nonlinear Tollmien-Schlichting/vortex interaction in three-dimensional boundary layers (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The instability of an incompressible three-dimensional boundary layer (that is, one with cross-flow) is considered theoretically and computationally in the context of vortex/wave interactions. Specifically the work centers on two low amplitude, lower-branch Tollmien-Schlichting waves which mutually interact to induce a weak longitudinal vortex flow; the vortex motion, in turn, gives rise to significant wave-modulation via wall-shear forcing. The characteristic Reynolds number is taken as a large parameter and, as a consequence, the waves' and the vortex motion are governed primarily by triple-deck theory. The nonlinear interaction is captured by a viscous partial-differential system for the vortex coupled with a pair of amplitude equations for each wave pressure. Three distinct possibilities were found to emerge for the nonlinear behavior of the flow solution downstream - an algebraic finite-distance singularity, far downstream saturation or far-downstream wave-decay (leaving pure vortex flow) - depending on the input conditions, the wave angles, and the size of the cross-flow.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-106184 , ICOMP-93-17 , E-7889 , NAS 1.15:106184
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  • 2
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    Linear and nonlinear pattern selection in Rayleigh-Benard stability problems (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A new algorithm is introduced to compute finite-amplitude states using primitive variables for Rayleigh-Benard convection on relatively coarse meshes. The algorithm is based on a finite-difference matrix-splitting approach that separates all physical and dimensional effects into one-dimensional subsets. The nonlinear pattern selection process for steady convection in an air-filled square cavity with insulated side walls is investigated for Rayleigh numbers up to 20,000. The internalization of disturbances that evolve into coherent patterns is investigated and transient solutions from linear perturbation theory are compared with and contrasted to the full numerical simulations.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-104007 , A-93048 , NAS 1.15:104007
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  • 3
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    Collective effects of temperature gradients and gravity on droplet coalescence (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The interaction and coalescence of small spherical drops in dilute, homogeneous dispersions are considered theoretically under conditions, where drop motion results from gravity settling and thermocapillary migration acting simultaneously. A trajectory analysis is used to predict pairwise collision rates, and population dynamics equations are solved to predict the time evolution of the droplet size distribution. The rate of droplet collisions and growth may be reduced dramatically by antiparallel alignment of the gravitational and thermocapillary velocities. For such antiparallel alignment with the gravitational relative velocity exceeding the thermocapillary relative velocity for two widely separated drops, there is a 'collision-forbidden region' in parameter space. This occurs because the gravitational relative velocity decays more rapidly with decreasing separation distance between the drops than does the thermocapillary relative velocity, and so the resultant relative velocity along the line-of-centers from these two sources combined becomes zero at a finite separation and the drops are unable to collide. As a result, small drops which initially collide and coalesce due to thermocapillary motion will only grow until they reach a critical size for which the oppositely directed gravitational motion balances the thermocapillary motion.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 5; 7; p. 1602-1613.
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  • 4
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    A hydrodynamic model of the oscillating screen viscometer (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The viscometer consists of an oscillating screen immersed in a fluid and free to rotate about an axis in its plane. The viscosity can be determined from the measured ratio of the periodic driving force to the screen motion when an adequate hydrodynamical model of the immersed oscillator is available. The screen is formed by a square mesh of thin wire whose dimensions invite comparison with asymptotic results for narrow hollow bodies translating in Stokes flow. These indicate that the closed hole structure of the grid plays an important role in determining its motion. It is shown that this role diminishes as the frequency increases. The computed results, obtained from a system of linear equations, are consistent with experimental values over the appropriate range of frequency.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 5; 9; p. 2095-2103.
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  • 5
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    An algorithm for solving the perturbed gas dynamic equations (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The present application of a compact, higher-order central-difference approximation to the linearized Euler equations illustrates the multimodal character of these equations by means of computations for acoustic, vortical, and entropy waves. Such dissipationless central-difference methods are shown to propagate waves exhibiting excellent phase and amplitude resolution on the basis of relatively large time-steps; they can be applied to wave problems governed by systems of first-order partial differential equations.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 93-0664 , ; 11 p.|AIAA, Aerospace Sciences Meeting and Exhibit; Jan 11, 1993 - Jan 14, 1993; Reno, NV; United States
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  • 6
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    Experimental study of two interacting drops in an immiscible fluid (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Experiments were performed in order to elucidate the effects of hydrodynamic interactions between two drops on their gravity-induced relative motion. The relative trajectories of two drops, their relative velocities, and the travel time for them to flow around each other were measured for different initial horizontal separations. Two size ratios and two viscosity ratios were investigated. Hydrodynamic interactions significantly reduce the relative velocity of two nearby drops and cause them to flow around each other with curved trajectories, resulting in a longer duration of the close encounter, compared with that for two non-interacting drops. These effects increase with decreasing drop separation, decreasing size ratio, and increasing viscosity ratio. Experimental results are in good agreement with theoretical predictions, except when the drops become sufficiently close that interface deformation occurs.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); p. 227-239.
    Format: text
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