Spanwise Variations in Aerodynamic Damping of an Oscillating Annular Compressor Cascade

Abstract

Aeroelastic instability in turbomachinery is one of the severe problems limiting its performance. Of particular interest is the phenomenon of stall flutter in compressors, which occurs when blades encounter large incidence flows. With the objective to understand the aerodynamics associated with stall flutter, the present experimental study is conducted on a subsonic annular compressor cascade. Five consecutive blades are oscillated, with the central blade instrumented for unsteady surface pressure measurements. The flow incidence is established using inlet guide vanes to provide three inflow profiles, representative of nominal, near-stall, and poststall incidences. With the blades oscillating at specific interblade phase angles and reduced frequencies, the stability of the cascade is determined globally and locally in terms of aerodynamic damping. The near-hub flow is distinctive due to the thickened boundary layer, resulting in an irregular variation of pressure with low magnitudes, eventually approaching negative stability. At larger incidences, due to the low-amplitude fluctuations in pressure at all spans, the overall stability is reduced. The present work also describes and rationalizes the nature of the dependence of blade unsteady pressure distribution on reduced frequency and incidence.