Axisymmetric Casing Optimization for Transonic Compressor Rotors

Abstract

In the present work, a method for tip clearance loss reduction by casing contouring above a transonic rotor with a constant clearance height is presented. The proposed method is found to be effective especially at design point conditions, which marks an important difference to nearly all well known casing treatment configurations. The Stage 3 of the DLR test RIG 250 was used as vehicle for the following work. In order to achieve a well increased performance of Stage 3 of the test rig an automated process chain is used to couple the DLR in house Optimizer AutoOpti (Voß et al., 2006; Siller et al., 2009) with the DLR 3D Navier-Stokes flow solver TRACE (Kügeler, 2004; Nürnberger, 2004). Kriging and neural networks are used as accelerating surrogate metamodels in the optimization process. It has been found that similar to casing contouring in high pressure stages (Kröger et al., 2009b) an optimized casing and blade tip contour in transonic stages with small clearance heights lead to a smaller overall pressure loss coefficient of the clearance flow so that the endwall blockage can be reduced and the stage performance can be improved up to 0.4% at design point conditions.