Unsteady aerodynamic blade row response is generally categorized as either subresonant or superresonant, with an acoustic resonance at the points where these regions meet. Although these far field acoustic responses are critical to obtaining correct predictions from linearized unsteady flow models, they are a subject of some controversy, both analytically and experimentally. In this paper, multistage axial flow compressor acoustic resonance conditions, including both subresonant and superresonant unsteady aerodynamic response in the immediate vicinity of an acoustic resonance, are experimentally investigated. This is accomplished by quantifying these acoustic resonance and subresonant and superresonant blade row interaction phenomena in terms of their effect on the rotor blade row periodic unsteady pressure response. The subresonant and superresonant acoustic environments are established by changing the number of vanes while maintaining the number of rotor blades, thereby altering the unsteady stator-rotor interactions and the interblade phase angle and by varying the Mach number without changing the blade row interactions. First the first stage rotor row periodic unsteady pressure response to a downstream stator-rotor interaction generated acoustic wave is studied. Then, the gust unsteady aerodynamic response of the first stage rotor row due to IGV wakes, with the IGV-instrumented first stage rotor itself configured to generate subresonant and superresonant conditions is considered. Appropriate data are correlated with predictions.

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