Unsteady Deffuser Flow in a Transonic Centrifugal Compressor

The paper deals with the clarication of the unsteady, transonic ow phenomena occurring in the vaned diuser area of a high pressure ratio centrifugal compressor stage. A description of the test rig, the measurement technique applied and a brief description of the steady 3D code used for the theoretical investigations are given. The measured stage characteristic and the mean diuser pressure rise as deduced from the 3D calculations are presented. The unsteady ow character in the vaned diuser region is experimentally resolved with the help of laser measurements performed for the whole diuser region, from impeller exit up to the vaned diuser exit. A comparison with the results of a steady state 3D calculation carried out separately for the rotor and diuser shows good agreement with reality, especially with the ow in the rear part of the diuser, where the real ow was found to be almost steady.