In high pressure compressors large tip clearances can occur in the rear stages especially during transient operation. This can lead to a reduced operating range and performance of the compressor. One simple means to reduce the negative effects of a rotor tip clearance increase can be circumferential groove casing treatments. Their ability to improve the operating range of a compressor is well-known for several decades.
In this paper, an experimental study to investigate the influence of three different circumferential groove casing treatments on a low speed axial research compressor with very large rotor tip clearances (5% of annulus height) is presented. Two single-groove and one double-groove casing treatments have been tested. The grooves are positioned from 31% to 69% axial chord. The compressor characteristics of the smooth wall and the three groove configurations are discussed as well as selected five-hole probe measurements of the flow field downstream the rotor. It can be shown that all grooves are able to improve the operating range of the compressor. Furthermore, an improvement of efficiency due to the casing grooves can also be observed in certain operating points.