Blade-Row Interaction Effects on Unsteady Stator Loading in an Embedded Compressor Stage

Blade-row interactions drive unsteady blade forces in compressors. This paper presents a perspective on understanding how the pitchwise variations in the flow at the exit of the rotor affect the surface pressures on the downstream vane. The rotor wakes and tip leakage flows are the primary unsteady flow features that drive unsteady lift on the vane. However, those rotor flow features are affected by their interaction with the wakes from upstream vanes. Thus, the interaction with stator 1 and rotor 2 must be understood to adequately characterize the interaction between rotor 2 and stator 2. This paper uses vane clocking, or the circumferential shift in successive vane rows of similar counts, to illuminate these blade-row interaction effects on the downstream vane surface pressure distribution. To accomplish this, experiments are performed in a three-stage axial compressor where high-frequency response pressure transducers are flush-mounted in the stator 2 pressure and suction surfaces are flush-mounted at 50 and 80% spans. Results show that rotor 1-rotor 2 interactions contribute significantly to the changes in unsteady stator surface pressure over the course of a rotor revolution. Also, the rotor 1-rotor 2 interaction levels change in the pitchwise direction downstream of the rotor; thus, the changes in surface pressure are affected by vane clocking. Furthermore, the rotor tip leakage flow is an additional contributor to the unsteady stator surface pressures measured at 80% span, providing an additional pressure peak per blade passing, and thus more high-frequency content (twice the blade-passing frequency).