A Method for Predicting the Noise of a Tip-Jet Driven Rotor

The use of tip jets to provide the torque to power rotor blades has long been considered as an alternate approach to a shaft driven rotor system. However, large tip-jet exit velocities are needed to provide sufficient jet thrust to power the rotor; hence, these jets can generate very large noise levels when compared to the usual sources of rotating blade noise. This paper demonstrates a new approach to predict the noise from such a design. The methodology uses a derivative of the SAE ARP876 Revision D code to compute the tip-jet noise and PSU-WOPWOP to compute the rotational noise. Noise predictions for the Fairey Rotodyne aircraft are compared with acoustic measurements to provide a limited validation of the noise prediction methodology. The prediction method is also demonstrated through a brief investigation of design constraints and their impact the rotor noise levels.