Tone Noise Prediction of a Propeller Operating in Nonuniform Flows

摘要

This paper examines the tone noise generation by propellers operating in a nonuniform mean flow. A numerical approach is proposed, based in the frequency domain, for predicting far-field propeller noise, which requires the aerodynamic sources to be integrated over the actual blade surface, rather than over the mean-chord surface. The prediction of the radiated far-field tonal noise for a four-bladed propeller operating in a nonuniform mean flow is performed. Validation of the method is presented through a detailed comparison between numerical predictions of the far-field noise and the measured data, in which excellent agreement is obtained, both in magnitude and directivity. This paper concludes that for first harmonic noise, matching the number of the main inflow harmonic of nonuniform flow with blade number creates a dipole-type symmetric directivity pattern, and mismatching appears as an asymmetric directivity pattern. Effects of a single inflow harmonic on the far-field radiated tonal noise are also quantified in this paper, which shows that when the matching condition is satisfied, the main inflow harmonic contributes most of the total radiated sound pressure, except at locations normal to the propeller axis. When the matching condition is not satisfied, however, the total radiated sound pressure is mainly caused by the dominant inflow harmonic and the inflow harmonic that equals the blade number.