Stall Margin Improvement by Use of Casing Treatments

The beneficial impact of casing treatments on the stall margin of tip-critical compressors has been proven many times. However, there is still no simple and general method to predict their actual effectiveness. The present work considers the axial velocity deficit that is generally observed at the blade tip. This so called tip-blockage is caused by the tip clearance flow. That is investigated for different configurations of the transonic compressor test facilities in Darmstadt and Notre Dame and the results are presented in this paper. Similar circumferential groove casing treatments were applied to different single-stage and 1.5-stage compressors. They all had a tip critical behavior in common, but exhibited different design philosophies. The effectiveness of similar casing treatments on different stages was observed. A new method for calculating tip-blockage is introduced based on compressor performance and the results of a through-flow tool. A direct link between blockage growth and stall margin improvement was found for circumferential grooves casing treatments. Additionally, the results of an axial slot casing treatment are taken into account.Copyright © 2013 by ASME