Modeling Capability for Cavity Flows in an Axial Compressor

Abstract

Seal-teeth cavity leakage in a shrouded stator blade deteriorates the performance of an axial compressor. This impact of shrouded stator seal-teeth cavity flows on compressor performance is demonstrated by presenting a sensitivity study with different seal-teeth clearances. A parametric definition of the cavity geometry (including the seal teeth) is created for an axial compressor, which allows for variation in seal teeth design, clearance and cavity shape. One and a half subsonic stages (rotor-stator-rotor) of a 10 stage axial compressor derived from the EEE design is considered to perform a computational fluid dynamic study. A NLH calculation is performed to account for the unsteady effects across the rotor-stator interface. Accuracy of the NLH calculations is determined by a comparison with time-marching results. For mixing plane calculations the location of the rotor-stator interface relative to the upstream and down-stream cavity connections is crucial. Comparison for mixing plane calculation at different rotor-stator interface is made with NLH results. For this configuration the low momentum leakage flow through the cavities gets entrained in the power stream upstream of the stator which increases the near hub blockage for the stator. Excessive near hub blockage alters the outlet flow conditions for the stator which changes the incoming flow for the down-stream rotor. A vortical flow structure exists at the upstream and downstream cavity connections which changes with the increase in clearance and defines the flow going into and coming out of the cavity. An increase in seal-teeth cavity clearance is shown to deteriorate compressor efficiency up to 0.86% for the largest clearance analyzed. The parametric design and simulation process presented represents the first step in a design optimization process that accounts for cavity flows and seal leakage. The seal-teeth cavity should be modeled correctly to account for the correct blockage and loss distribution. It should also be integrated into the airfoil design at an early stage.