Noise Due to Interaction of Boundary-Layer Turbulence with a Compressor Rotor

Abstract

The radiated sound due to a compressor or propulsor rotating blade row was investigated under various operating conditions and inflows. The propulsor was operated in air with different blade space-to-chord ratios, different flow coefficients and differing turbulence (nonisotropic) inflows. The inflows ingested were: 1) the natural boundary layer on the hub and annulus wall, 2) a tripped boundary layer on the hub, and 3) a fully developed boundary layer on the hub. The turbulence properties were also altered by placing a grid at the inlet. The mean velocity profiles, turbulence intensities, length scales, and energy spectra of the inflow, as well as nearand far-field acoustic spectra, were measured. A parametric investigation of the effect of inflow characteristics on the radiated sound was made. Several length scales were found to exist simultaneously. The noise due to small scale turbulence seemed to depend on the ratio of the square of the turbulence velocity normal to the blade divided by the axial length scale. The long eddies (compared to blade spacing) were primarily responsible for discrete tone production. Nomenclature ABL,NBL,FDBL = artificial, natural, and fully developed boundary layer, respectively B = number of blades c = blade chord CL =lift coefficient based on the cascade mean velocity Eu.u.(k) = spectrum function of turbulence kinetic energy k = wave number