Experimental Investigations of an Oscillating Annular Compressor Cascade at Reverse Flow Conditions

While the advancement of computing hardware now enables accurate predictions of flutter and forced response at normal flow conditions during the compressor design phase, aeroelastic computations at off-design or reverse flow conditions remain a challenging task. During the flow reversal sequence of a surge cycle, complex aerodynamics occur which make the accurate prediction of the unsteady forces acting on the blades difficult to assess. The main objective of this study is to increase the physical understanding of the unsteady contributions acting on the blades during the reverse flow sequence of a typical deep surge cycle. The approach adopted consisted in performing aeroelastic investigations on an annular compressor cascade at established reverse flow conditions. The cascade blades were equipped with unsteady pressure transducers and were excited to oscillations in travelling wave mode. In this paper, the blade surface fluctuating pressures recorded are analyzed for one flow operating condition. The measurements enable the determination of the blade aerodynamic stability and highlight the unsteady physical mechanisms present during the surge blow-down phase. For the investigated test case, steady-state numerical computations were carried out in parallel to the measurements to enable the comparison between both approaches.