Effects of the foam metal casing treatment on aerodynamic stability and aerocoustic noise in an axial flow compressor

A kind of foam metal casing treatment (FMCT) is proposed and experimentally tested on a low-speed axial flow compressor in this work. Foam metal is a foam-like substance with a lightweight structure but a certain strength. Both time-mean and high-response instrumentation are applied to capture the steady and unsteady performances of the compressor. Initially, parametric experimental measurements on axial location of foam metal over rotors are performed with respect to stability enhancement and noise reduction. It is found that the stall margin improvement (SMI) and the aerodynamic efficiency loss are functions of the axial location of the foam metal. Particularly, the SMI maxima appears at CT7 with a certain amount of aerodynamic efficiency loss. In analyzing the results measured over and downstream of the rotor, it is suggested that the release of rotor tip loading may be a stability improvement mechanism of FMCTs. Furthermore, comparison in the stall inception process of the axial flow between the compressor with the solid-wall and the implementation configuration shows that, in solid-wall casing condition, the compressor experiences a spike-type stall inception, however in CT7, the compressor goes through a modal-type process. Finally, conclusions and suggestions are given based on the findings.