Accession Number : ADA300740

Title :   Direct Numerical Simulations of Separated and Separated-Reattaching Flows on Massively Parallel Processing Computers.

Descriptive Note : Master's thesis,

Corporate Author : ILLINOIS UNIV AT URBANA

Personal Author(s) : Najjar, Fady M.

PDF Url : ADA300740

Report Date : APR 1994

Pagination or Media Count : 323

Abstract : Direct numerical simulations of separated-reattaching and separated flows have been performed on massively parallel processing computers. Two basic geometrical configurations have been studied: the separated-reattaching flow past a normal flat plate with an attached downstream splitter plate and the separated flow past a flat plate held normal to a uniform stream. A high-order finite-difference formulation on collocated grids has been developed to perform unsteady fluid flow simulations in rectangular geometries. The numerical procedure is based on a fifth-order upwind-biased scheme for the convective terms and a fourth-order accurate stencil for the diffusive terms. A direct solver based on eigenvalue decomposition has been developed for the pressure-Poisson equation. A mixed Fourier spectral /finite difference formulation is used for the spanwise discretization, and a data-parallel algorithm has been developed for the CM-5. The performance of the algorithm has been evaluated on various grid sizes in model flow problems and for different partition sizes. The characteristics of the separated-reattaching flow have been investigated through two-dimensional simulations in the steady and unsteady regimes. The shedding mechanism is characterized by two major modes at Re = 250 and a single mode at Re = 375 and 500. Further, the instability of the separated shear layer is found to be consistent with inviscid theory. For the two-dimensional study of the separated flow past a normal flat plate, the time-mean flow quantities are observed to be over-estimated compared to the experiments. The time-mean drag coefficient is also over-predicted by a factor of up to 2. This is attributed to the high coherence of the vortices predicted by the two-dimensional simulations

Descriptors :   *MATHEMATICAL MODELS, *PARALLEL PROCESSING, *FLOW SEPARATION, SHEAR PROPERTIES, ALGORITHMS, COMPUTERIZED SIMULATION, COMPUTATIONS, SIZES(DIMENSIONS), INTERACTIONS, COMPUTERS, LAYERS, FORMULATIONS, GRIDS, NUMERICAL ANALYSIS, COHERENCE, CONVECTION, VORTICES, FINITE DIFFERENCE THEORY, PLATES, RECTANGULAR BODIES, WAKE, TWO DIMENSIONAL FLOW, UNSTEADY FLOW, NUMERICAL METHODS AND PROCEDURES, INVISCID FLOW, FLUID FLOW.

Subject Categories : Operations Research
      Fluid Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE