Upstream-propagating acoustic waves interacting with a compressible cascade

Abstract

Phase-locked, unsteady, surface-pressure measurements were made on the vanes of a compressible cascade, for inlet Mach numbers up to 0.5, which resulted in Mach numbers through the vanes of up to 0.73. Flow unsteadiness was produced by shedding from circular cylinders positioned at a distance of 80 percent chord downstream of the vane row (rearward forcing). When the unsteady pressure response from this rearward forcing was compared with the response from forward forcing, rearward forcing resulted in the same order of unsteady surface pressure response as forward forcing. Decomposition of the ensembled, phase-locked signals for rearward forcing demonstrated unambiguous position-vs-phase curves that showed that the unsteady disturbances originate from downstream and propagate forward through the vane row at acoustic speeds into the oncoming flow. These acoustically-radiated disturbances appear to have elicited two previously-unexpected response amplification mechanisms: a possible trailing-edge singularity; and a Mach number-related amplification that may be evidence of acoustic blockage. (Author)