Acoustic theory of the many-bladed contra-rotating propeller: analysis of the effects of blade sweep on wake interaction noise

摘要: An analytical model is presented for the wake interaction tones produced by a contra-rotating propeller. We re-cast usual far-field radiation formulae as double integral over nominal propeller source annulus. Assuming that number of blades on both propellers large, we evaluate asymptotically in terms its leading-order contributions from interior stationary or boundary critical points which represent specific locations annulus dominate sound radiation. The asymptotic approach powerful producing results form one-line algebraic contain no integrals special functions yet remain accurate. asymptotics show sweep not necessarily beneficial and can cause blade design to become particular directions continuum distributed along line higher-order result thus an enhanced radiated field. paper also shows how are completely consistent with sub- super-critical gust response swept blade. Tones low zero azimuthal mode order treated cases that, reduces, becomes concentrated around flight axis where even solutions possible, including rings annuli Full numerical calculations confirm accuracy approach.