Experimental Validation of Lifting Surface Theory for Rotor-Stator Interaction Noise Generation

An important element in the National Aerospace Laboratory NLR prediction model for rotor-stator interaction noise is the unsteady lifting surface theory for a rotating blade row. To validate this lifting surface theory, a wind-tunnel experiment has been carried out using a through-flow nacelle with a hub, a 16-bladed rotor, and an 18-vane stator. Two mechanisms of sound generation were recognized. As usual in rotor-stator configurations, sound was produced by interaction of rotor viscous wakes with the downstream stator vanes. In addition, due to the small gap between rotor and stator, sound was generated by interaction of the stator vanes, with flow distortions caused by the thickness of the rotor blades and vice versa. Trip wires were attached to blades and vanes to simulate high-Reynolds-number flow. Unsteady pressures were measured on a stator vane, on a rotor blade, and in the inlet. Experiment and theory are briefly described, and results from both are compared. For most of the measured cases, the agreement is good.