Unsteady Leading Edge Suction Effects on Rotor-Stator Interaction Noise

A strictly linear analysis of the sound generated by an unleaned stator yields a vanishing amplitude for modes with zero circumferential periodicity. In such a case higher-order effects become relevant. In the present study the higher-order effect of stator leading-edge suction on radiated sound is addressed. By a local analysis in the vicinity of the leading edge, a suction force can be restored from the first-order theory. This suction force oscillates at twice the frequency of the associated blade loading. Numerical examples show that the effect provides a realistic floor level for the sound that otherwise would seem to vanish. For non-zero circumferential modal wave numbers, the effect can increase the acoustic intensity by as much as 10 dB.