Aerodynamic design of abradable liners with integrated endwall treatments for axial compressor rotors

In this study endwall treatments, which are integrated into an abradable liner, are used to reduce the liner solidity, defined by the volumetric proportion between endwall treatments and solid casing. Consequently the milled off amount of liner material during the rubbing process is decreased. The mechanical stresses in the rotor blades are thus supposed to be reduced, so that liner materials with higher strength can be used or additional blade tip coatings are dispensable. Accordingly, the purpose of the present study was to develop geometries of endwall treatments, which reduce the liner solidity as much as possible without degrading the stage performance of the test compressor. The focus of the work lies exclusively on the aerodynamics. Investigations were made by steady and unsteady computational fluid dynamics on a transonic single stage axial compressor with two different tip clearance sizes (0.64%/1.28% span). The developed configurations resemble casing treatments, comparable to axial slots and circumferential grooves, which are adapted to the specific tasks of liners. Solidity could be reduced by as much as 29% with negligible efficiency degradation for small tip gaps and increased efficiencies for large tip clearances.