Modular Prediction Scheme for Blade Row Interaction Noise

A previously developed method for the prediction of contrarotating propeller noise is extended, with minimal modification, for application to many-bladed configurations. The resultant scheme is applied to rotor-stator, stator-rotor, and rotor-rotor aerodynamic interactions on ducted rotors. Two classical wake models and a semiempirical wake model are considered; these models are compared with wake data from a fan rig, and it is shown that the classical models are far superior to the semiempirical model. Far-field predictions of sound power are compared with measured data from a conventional single-stream fan rig and from a contrarotating ducted fan model. Theory and noise data are shown to agree reasonably well for both sets of data and at all frequencies, without taking any account of rotor blockage. The results suggest that the level of agreement could be improved further by some modifications to the wake model and by the inclusion of rotor blockage effects in the prediction scheme. (Author)