Innovative Methodology for Cancelling Contaminating Noise in Turbulent Fluid Flow Environments.

摘要

A method is presented for the cancellation of wide band contaminating noise occurring within internal flow configurations such as rectangular channels and pipes. Facility generated noise within these flow systems contaminates the turbulent wall pressure signature at low frequencies thus preventing the possible extraction of useful information. The proposed methodology utilizes the signals from two flush mounted wall pressure transducers. A first estimate for the one and two-point spectral densities is obtained using a least mean square algorithm. A secondary correction to this estimate is obtained by taking advantage of the planar homogeneity of the turbulence. The application of the technique is demonstrated in a fully developed turbulent channel flow for which more than 40 dB cancellation is obtained at low frequencies. In this low frequency range, the power spectral density is shown to have an approximate quadratic dependence, substantiating past theoretical predictions reported in the literature. In addition, the two-point spectral densities are adequately resolved, substantiating a convective pattern which rapidly loses coherence which is typical in such flow configurations. Keywords: Noise cancellation, Wall pressure, Turbulent flow, Hydrodynamic flow noise, Channel flow. (jhd)