Status of Research on Propeller Noise and Its Reduction

Abstract

The basic concepts concerning the mechanism of propeller noise generation are reviewed, and equations for calculating the noise field both near and far from the propeller are given. The problem of noise due to non-steady airloads on the blades, and differences in noise from the approaching and retreating blades are discussed. Effect of tip speed, number of blades, blade thickness, and blade width are considered, and it is shown that reducing the tip speed and increasing the number of blades are probably the most effective means of reducing the efficiency of noise generation and alleviating the noise problem. Noise characteristics of such special types as the supersonic, dual-rotating, tandem, and shrouded propeller are also presented. Studies of propeller weight show that substantial noise reduction on transport type propellers would result in a considerable weight penalty. For the propeller-driven aircraft in the 400 to 500 mph speed range, the slower turning quieter propeller is likely to have better propulsive efficiency than the noisier high speed propeller. Hence, in this speed range, the weight penalty of the quieter propeller may be offset by its higher propulsive efficiency.