Unsteady pressure distributions around compressor vanes in an unsteady, transonic cascade

Abstract

Abstract : Unsteady surface pressure measurements were made at various chord locations on the turning vanes in an unsteady, compressible- flow, linear cascade. The turning vanes were made from production stator vanes from the fan stage of a Garrett F1O9 engine. The cascade unsteady forcing was produced by von Karman shedding from a row of circular-cylinder rods positioned at either 80% chord upstream of the turning vanes (forward forced) or at 80% chord downstream (rearward forced). Nominal time series of many complete cycles of the unsteady pressure response required acquiring the phase-locked response from eight instrumented vanes, each having pressure transducers at two chord locations. Unsteady pressure response from rearward forcing was of the same order as that for forward forcing. Decomposition of the ensembled, phase- locked signals into their primary and harmonic components provided insight into the amplitude decay rates and wave propagation direction within the cascade row. Although the unsteady cascade was limited to passage Mach numbers near 0.75, the rearward forcing cases indicated a suction-surface, amplification that increased with increasing Mach number. This 'bulge' appears to be compatible with the acoustic blockage phenomenon. Forward forcing of the stator vane row showed the importance of the constructive and destructive interference between convective wakes and potential disturbances that propagate at acoustic speeds. These interactions created unexpected unsteady surface pressure profiles which could be important for analysis of stator vibration modes. (AN)