ANALYSES OF URANS AND LES CAPABILITIES TO PREDICT VORTEX SHEDDING FOR RODS AND TURBINES

P. Ferrand, J. Boudet, J. Caro

Ecole Centrale de Lyon – LMFA – UMR 5509 36, avenue Guy de Collongues 69134 Ecully (France) pascal. ferrand@ ec-lyon. fr

S. Aubert, C. Rambeau

Fluorem, Ecully (France)

Abstract The objective of this study is to evaluate the capability of codes to simulate vor­tex shedding that occurs at the trailing edge of turbine blades. Firstly, unsteady RANS simulations (various k — w models) are presented on the VKI turbine, and the results are compared to experiments. Next, results are interpreted for an academic test-case of fbw past a rod. This latter configuration allows a deeper analysis and provides an outlook by the use of large-eddy simulation (LES). It appears that URANS provides qualitative results, and LES is an interesting way to get accurate predictions.

1. Introduction

Large unsteady coherent structures appear downstream turbine blade with thick trailing edge. These "von Karman” vortex structures are similar to vortex shedding in wake of a rod. The phenomenon has been investigated experi­mentally by many authors at low (Han and Cox, 1983, Cicatelli and Sieverd – ing, 1997) and high speed (Sieverding et al., 2003). The experimental results present quantitative information on unsteady pressure, velocity, and tempera­ture. Sieverding’s results are a precious source of analysis and validation of numerical simulations. The presented results try to evaluate the capabilities of URANS and LES to predict these phenomena. In fact, through these differ­ent models, the question is to know if the turbulent scales interact or not with

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K. C. Hall et al. (eds.),

Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines, 381-393. © 2006 Springer. Printed in the Netherlands.

macroscopic vortices. If yes, LES must be performed to simulate vortex shed­ding process, if no, URANS can be enough. Experimental results (Sieverding et al., 2003) on turbine blade, and presented results, are based on European Research Projects "Turbulence modeling for unsteady fbws in axial turbines”.