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  • 1
    ISSN: 0271-2091
    Keywords: Cavity Flow ; Incompressible Flow ; Control-Volume Formulation ; Navier-Stokes Equations ; QUICK ; Convection Scheme ; Taylor-Görtler Vortices ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Previous three-dimensional simulations of the lid-driven cavity flow have reproduced only the most general features of the flow. Improvements to a finite difference code, REBUFFS, have made possible the first completely successful simulation of the three-dimensional lid-driven cavity flow. The principal improvement to the code was the incorporation of a modified QUICK scheme, a higher-order upwind finite difference formulation. Results for a cavity flow at a Reynolds number of 3200 have reproduced experimentally observed Taylor-Görtler-like vortices and other three-dimensional effects heretofore not simulated. Experimental results obtained from a unique experimental cavity facility validate the calculated results.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0271-2091
    Keywords: advective transport ; semi-implicit ; conservative ; unconditionally stable ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A one-dimensional scalar transport method which is appropriate for simulations over a wide range of Courant number is described. Von Neumann stability and matrix invertibility are guaranteed for all Courant numbers and the method has less diffusive and dispersive error than simpler implicit methods. It is implemented for vertical scalar transport in a three-dimensional hydrodynamic model, with horizontal transport discretized explicitly. The method is applied and compared with simpler semi-implicit methods in several test cases and used for a simulation of scalar transport in an estuary. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 208-218 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of experiments has been conducted in a lid-driven cavity of square cross section (depth=width=150 mm) for Reynolds numbers (Re, based on lid speed and cavity width) between 3200 and 10 000, and spanwise aspect ratios (SAR) between 0.25:1 and 1:1. Flow visualization using polystyrene beads and two-dimensional laser-Doppler anemometer (LDA) measurements have shed new light on the momentum transfer processes within the cavity. This paper focuses on the variation, with Re and SAR, of the mean and the rms velocities profiles, as well as the ∼(U'V') profile, along the horizontal and vertical centerlines in the symmetry plane. In addition, the contribution of the large-scale "organized structures,'' and the high-frequency "turbulent'' velocity fluctuations to the total rms is examined. At low Re, the organized structures account for most of the energy contained in the flow irrespective of SAR. As the Re increases, however, so does the energy content of the higher frequency fluctuations. This trend is not independent of SAR; a reduction in the SAR causes the "organized structures'' to again become more evident.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 3870-3883 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Laboratory experiments have been performed for a double diffusive system in which opposing vertical gradients of temperature and salinity are heated from one side. Details of the internal structure of the intrusions that form along the heated endwall are discussed. Fingering motions and convective overturns are prominent characteristics of the internal intrusion structure, particularly when the rate of lateral heating is high relative to the strength of the ambient vertical density gradient. Analysis of the overturning scale indicates that the RMS size of the overturns is typically 10%–30% of the total layer thickness. Comparison of the flow inside the convective layers with that which develops in a long box heated and cooled at opposite sides based on the analysis of Jeevaraj and Imberger [J. Fluid Mech. 222, 565 (1991)] shows poor agreement when molecular values of the diffusivity and viscosity are used in the theory. However, moderate increases in the diffusivity values (to account for increased vertical mixing) give good agreement between the experiments and theory. Building on the results of Schladow et al. [J. Fluid Mech. 236, 127 (1992)], further evidence of the ability of the intrusions to continue propagating following removal of the endwall heating is presented. Modification of the flow field ahead of the intrusion fronts can create conditions for which the stability ratio, Rρ, drops below a critical value, resulting in continued propagation of the intrusions. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Our objective in this study is to study inhomogeneous stratified shear flows using large eddy simulation; stratified pressure-gradient-driven channel flow was selected. The flows can be separated into three regimes: buoyancy affected, buoyancy controlled, and buoyancy dominated flows. The regime boundaries are defined by Richardson and Reynolds numbers based on the friction velocity. Buoyancy affected flows remain actively turbulent and attain a statistical steady state that resembles a lower Reynolds number unstratified flow. Flows in the buoyancy controlled regime are not in equilibrium. In the cases studied, an asymmetry develops with respect to the channel centerline leading to one-sided turbulence. Eventually, the "inactive" half undergoes a transition initiated by the active half and symmetry is restored. At higher Richardson numbers, the flows are buoyancy dominated, the near-wall burst-sweep process is completely disrupted and turbulence production ceases, leading to relaminarization. In relaminarizing flows, the inner and outer regions behave nearly independently. While the inner region turbulence decays monotonically, large-scale restratification, internal waves, and potential energy-driven motions are observed in the outer region. The simulation results are used to construct a physical model of stratified wall-bounded flows. Stable stratification weakens the interaction between the inner and outer regions by decreasing the vertical transport, leading to near-decoupling of the two layers at strong enough stratification. The notion that the disappearance of the log region marks the onset of buoyancy control provides a criterion for estimating the Richardson number delineating the transition from buoyancy affected to buoyancy controlled flows. Data that should be useful for creating parametrizations for prediction of stratified flows are also presented. © 2000 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 3186-3196 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dynamic subgrid-scale eddy viscosity model of Germano et al. [Phys. Fluids A 3, 1760 (1991)] (DSM) is modified by employing the mixed model of Bardina et al. [Ph.D dissertation, Stanford University (1983)] as the base model. The new dynamic mixed model explicitly calculates the modified Leonard term and only models the cross term and the SGS Reynolds stress. It retains the favorable features of DSM and, at the same time, does not require that the principal axes of the stress tensor be aligned with those of the strain rate tensor. The model coefficient is computed using local flow variables. The new model is incorporated in a finite-volume solution method and large-eddy simulations of flows in a lid-driven cavity at Reynolds numbers of 3200, 7500, and 10 000 show excellent agreement with the experimental data. Better agreement is achieved by using the new model compared to the DSM. The magnitude of the dynamically computed model coefficient of the new model is significantly smaller than that from DSM.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 619-622 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A two-dimensional numerical solution of the flow in a lid-driven cavity with a cutoff is compared with a physical experiment of the same flow. The Reynolds number of the flow is 3200. The results show that whereas the numerical solution is steady, the physical flow is unsteady and oscillates between three different flow modes. The oscillation is ascribed to unsteady three-dimensional structures in the flow.
    Type of Medium: Electronic Resource
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  • 8
    Publication Date: 2019
    Description: 〈div data-abstract-type="normal"〉〈p〉We investigate the interaction of a downslope gravity current with an internal wave propagating along a two-layer density jump. Direct numerical simulations confirm earlier experimental findings of a reduced gravity current mass flux, as well as the partial removal of the gravity current head from its body by large-amplitude waves (Hogg 〈span〉et al.〈/span〉, 〈span〉Environ. Fluid Mech.〈/span〉, vol. 18 (2), 2018, pp. 383–394). The current is observed to split into an intrusion of diluted fluid that propagates along the interface and a hyperpycnal current that continues to move downslope. The simulations provide detailed quantitative information on the energy budget components and the mixing dynamics of the current–wave interaction, which demonstrates the existence of two distinct parameter regimes. Small-amplitude waves affect the current in a largely transient fashion, so that the post-interaction properties of the current approach those in the absence of a wave. Large-amplitude waves, on the other hand, perform a sufficiently large amount of work on the gravity current fluid so as to modify its properties over the long term. The ‘decapitation’ of the current by large waves, along with the associated formation of an upslope current, enhance both viscous dissipation and irreversible mixing, thereby strongly reducing the available potential energy of the flow.〈/p〉〈/div〉
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 9
    Publication Date: 2019
    Description: 〈div data-abstract-type="normal"〉〈p〉Results are presented from a laboratory study on the free-surface signal generated over an array of submerged circular cylinders, representative of submerged aquatic vegetation. We aim to understand whether aquatic ecosystems generate a surface signature that is indicative of both what is beneath the water surface as well as how it is altering the flow. A shear layer forms over the canopy, generating coherent vortex structures which eventually manifest in the free-surface slope field. We connect the vortex properties measured at the surface with measurements of the bulk flow, and show that correlations between these quantities are adequate to create a parameterized model in which the interior velocity profile can be predicted solely from measurements taken at the free surface. Experimental surface observations yield a Strouhal number that is twice the most amplified mode predicted by linear stability theory, suggesting that vortices may evolve between generation at the canopy height and their manifestation at the water surface. Additionally, the surface signal continues evolving with distance downstream, with vortices becoming spread farther apart and the passage frequency gradually decreasing. By the trailing edge of the canopy, surface-impacting boils emerge for canopies with higher submergence ratios, suggesting a transition from coherent two-dimensional rollers to transversely varying structures.〈/p〉〈/div〉
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 10
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