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Turbulence and Shear Flow Phenomena -1 First International Symposium

ISBN:
1-56700-135-1 (Print)

LARGE EDDY SIMULATION OF THE FLOW IN A BLADED DIFFUSER

Doru Caraeni
Dept. of Heat and Power Engineering, Fluid Mechanics, Lund Institute of Technology, SE-221 00 Lund, Sweden

Stephen Conway
Dept. of Heat and Power Engineering, Fluid Mechanics, Lund Institute of Technology, SE-221 00 Lund, Sweden

Laszlo Fuchs
Department of Mechanics, KTH, CICERO, SE-10044 Stockholm; Division of Fluid Mechanics Lund University Lund, 22363, Sweden

Abstract

The advances made in computer technology over recent years have lead to a great increase in the engineering problems which can be simulated using CFD. The computation of flows over complex geometries at relatively high Reynolds number is becoming more common using Large Eddy Simulations (LES), as recent reviews on the subject have shown (Piomelli, 98). Direct Numerical Simulations (DNS) of such flows is still beyond the capacity of today's largest supercomputers, requiring many millions of computational cells and excessive computational times. In addition, traditional Reynolds Averaged Navier-Stokes (RANS) methods fail for various reasons for many of the industrial applications of interest. In an increasing number of cases LES is seen as the only real alternative.
The anisotropic dynamic SGS models (Abba) have the potential of yielding better performances, for wall bounded flows. In this study, the Dynamic Divergence Model (DDM) has been used. It is a novel anisotropic dynamic SGS model (Held, 1998) (Conway, 1998), with independently determined coefficients in each direction. It has been designed to allow anisotropy, for wall bounded flows. Some results for the classical turbulent channel flow, while using DDM, are presented. The results obtained compare well with the experimental and DNS data.
LES has been used to solve the flow through a bladed diffuser positioned at the inlet to a gas turbine combustion chamber. Flows through such geometries at high Reynolds number are inherently time dependent, involve transition to and development of turbulence, fully three dimensional boundary layers, separation, etc. A simplified geometry has been studied previously (Conway, 1998). This work covers the next stage in the study. A new flow solver has been used in the present calculations. ParNAS3D is a parallel Navier-Stokes solver, that has been developed at LTH for simulations of engineering turbulent compressible flows, using LES.