Casing treatments are widely used to enhance the stall margin of fans or compressors of aircraft engines.However

the existing design of casing treatment is generally on the basis of trial and error method and its application always results in efficiency loss of fans or compressors.So

how to understand the mechanism of stall margin improvement with casing treatments and how to design better casing treatments have long been an area of vigorous research activity.Based on the knowledge of the unsteady characteristics caused by casing treatment

it is verified that recessed casing treatment can be modeled as a wall boundary condition

which can be calculated by means of vortex sound theory.In the present work

a series of experimental investigations were conducted with emphasis on the effect of unsteady casing treatments on the stall margin and efficiency of three different low speed fan/compressor facilities.The results show that the unsteady casing treatments do improve the stall margin without incurring recognizable efficiency loss of the concerned fan/compressor.