Effect of Inlet Turbulence on Compressor Noise

The sound generated by the interaction of inlet turbulence with a rotating compressor blade row is investigated. Currently, there are two theories relating the rotor geometry and blade aerodynamics to the spectrum of the radiated sound. These theories are extended to include the cascade effect by incorporating a cascade aerodynamic response function for the unsteady lift on the blades into their analyses. To experimentally study this noise source, an aeroacoustic compressor facility was designed and built. The parameters investigated include turbulence intensity and longitudinal integral length scale, blade speed, flow coefficient. The results indicate a definite increase in the overall sound pressure level and an increase in the spectrum level of the sound pressure with an increase in turbulence intensity. For integral length scales smaller than the blade spacing, the total sound power is found to be proportional to (turbulence velocity/integral length), 2 where turbulence velocity is rms value normal to the blade chord. Comparison of theoretical results with experimental data indicates one theory to predict the sound pressure level fairly accurately in a limited frequency range.