Propeller noise prediction

Abstract

Analytic propeller noise prediction involves a sequence of computations culminating in the application of acoustic equations. This paper describes the prediction sequence currently used by NASA in its ANOPP (Aircraft Noise Prediction) program. No attempt is made here to review the state of the art of noise prediction. Some elements of this sequence represent classic results while other represent the most recent publications. The elements of the sequence are called program modules. The first group of modules analyze the propeller geometry, the aerodynamics, including both potential and boundary layer flow, the propeller performance, and the surface loading distribution. This group of modules is based entirely on aerodynamic strip theory. The next group of modules deals with the actual noise prediction, based on data from the first group. Deterministic predictions of periodic thickness and loading noise are made using Farassat's time-domain methods. Broadband noise is predicted by the semi-emipirical Schlinker-Amiet method. Nearfield predictions of fuselage surface pressures include the effects of boundary layer refraction and (for a cylinder) scattering. Farfield predictions include atmospheric and ground effects. Comparisons are made to experimental data from subsonic and transonic propellers and NASA's future directions in propeller noise technology development are indicated.