Hybrid LES/RANS study of turbulent flow in a low speed linear compressor cascade with moving casing

In this work a robust hybrid LES/RANS model has been applied to the prediction of secondary flows in a linear compressor cascade with moving casing simulating the relative motion between blade and the casing. The hybrid LES/RANS model uses the well established z-f URANS model of Hanjalić et al. (2004) in the near wall region coupled with dynamic Smagorinsky LES. The switch between the two zones is based on a couple of parameters defining the boundary of interface region: the first one is a grid-detection parameter expressed as a function of the ratio between the turbulent and LES characteristic length scales while the switching to pure LES is obtained when the subgrid scale viscosity is greater than eddy viscosity (Delibra et al., 2010). We present hybrid LES/RANS results of a 3D linear compressor cascade with a tip leakage equal to 1.65% of chord. We compare two cascade configurations: with stationary casing and with moving casing. The second simulation allows to scrutinize the exclusive influence of the relative motion between casing and blades on the tip leakage vortex and the turbulent structures developing in the wake. The quality of the results and their agreement with experiments are encouraging in terms of prediction of the main flow characteristics and identification of turbulence structures. © 2010 by ASME.