On Acoustic Source Specification for Rotor-Stator Interaction Noise Prediction

This paper describes the use of measured in-duct fan noise source data to assess the effects of acoustic source specification on the prediction of externally radiated rotor-stator interaction noise. Specifically, the acoustic propagation and radiation elements of a recently developed coupled computational approach are used to predict the radiation of tonal rotor-stator interaction noise from a benchmark model scale fan. In addition to the use of “as-measured” data, randomization of source mode relative phases is also considered for specification of the acoustic source within the computational approach. Comparisons with sideline noise measurements are performed to investigate the effects of various source descriptions on both inlet and exhaust sideline noise predictions. The inclusion of ancillary (i.e., non-Tyler-Sofrin) modal source content is shown to have a much greater influence on the inlet results relative to the exhaust. Reasonable agreement between predicted and measured levels is achieved for the inlet, as well as the exhaust when the exhaust shear layer effects are taken into account. For the cases considered, phase randomized predictions follow statistical distributions similar to those found in previous statistical source investigations. The shape of the predicted directivity pattern relative to measurements also improved with phase randomization, having predicted levels generally to within one standard deviation of the measured levels.