Broadband Noise Prediction of Low Pressure Axial Fans Employing CFD-Flow Field Data

The broad band noise of a low pressure axial fan without guide vanes is computed and compared with measurements. The acoustic model uses the idea of randomly fluctuating forces which can be expressed in terms of the distribution of fluctuating pressure on the blade surface and a correlation area. The spectrum of the surface pressure is taken from measurements on surfaces and rotating fan blades in turbulent flows which are non-dimensionalized by the boundary layer displacement thickness and the freestream flow velocity. The boundary layer displacement thickness and the freestream flow velocity on the fan blades are estimated from detailed results of a numerical 3-D steady state flow field analysis. The computed sound power spectrum of the fan broad band noise agrees well with the measured spectrum.