The efficient numerical simulation of unsteady flow in a centrifugal compressor stage equipped with a vaned diffuser

Abstract

The scope of this paper is to present the Computational Fluid Dynamics (CFD) transient flow simulations of a centrifugal compressor stage with cavities at design point and at off design conditions. The cavities are included in the CFD model for several reasons. First the leakage flows and the windage effects are important to predict the absolute performance level of the stage (efficiency). Secondly the cavities also play an important role in the generation of the aerodynamic forcing on the impeller as well as in the prediction of the aerodynamic damping. The Time Transformation method, an extension of the time inclining method, is used in this work. The ability of the method to predict the impeller/diffuser interactions and cavity unsteady pressure response at design point and at off-design conditions is discussed. The respective contributions of the diffuser and impeller blade passages on pressure fluctuation amplitude and frequency content are studied.