Lifting Fan Noise Studies

Abstract

The paper reviews the results of an experimental investigation of noise radiated from a VTOL lifting fan inlet under static inflow conditions. The results are discussed in the light of recent theoretical and experimental conclusions on compressor noise radiation, combined with relevant data on the aerodynamic characteristics of the fan. The presence of high level discrete tones, up to four harmonics of the blade passing frequency superimposed over a broadband noise extending from 200 to 15,000 cps, is attributed to close spacing between rotor and stator blades, Low levels of broadband noise were observed to be caused by low levels of turbulence at the intake. Analysis of the limited results shows the variation of broadband noise as the sixth power of the velocity of the flow relative to the blade.