Experimental Investigation of the Rotor / Casing Treatment Interaction in an Axial Single-Stage Transonic Compressor

Abstract

In the design process of compressors for gas turbines, the application of casing treatments showed a substantial contribution to the enhancement of total pressure ratio and stability. The development of a treated casing endwall remains quite demanding due to the complicated flow features and interactions, particularly when applied to transonic rotors with strong shock systems. To achieve an insight into these flow mechanisms, the axial single-stage Darmstadt Transonic Compressor Test Rig was equipped with a casing treatment with 56 bend axial slots. Speedlines and exit plane measurements were made for design speed and for a completely subsonic flow field. Time resolved measurement techniques were chosen to investigate the rotorcasing treatment interaction. The casing treatment was designed to provide an optical access through two slots. In addition, the land between these slots was replaced with a glass insert. The assembly allowed phase-resolved particle image velocimetry investigations in the rotor tip area and inside the tip gap underneath one axial slot. Results showed an increase in stall margin for both operating conditions. Efficiency declined slightly. At design speed, a second shock structure develops when the casing treatment is applied. This additional shock front has considerable effect on the flow field. Vortices inside the slots account for the efficiency losses