A Study on the Effects of Non-uniform Inlet Flows upon Performance and Tonal Radiation from a Propeller Fan

초록

The flow fields and noise characteristics from a propeller fan designed previously under non-uniform inlet flow conditions were computed and measured to reveal the mechanism for tonal radiaition. An experimental study was carried out to vary the circumferential and radial components of harmonic incoming gust, and the intensity of turbulance deliberately. This paper reports the mearured acoustic similarity for various non-uniform inflow conditions and acoustic spectra for radial and azimuthal disturbance at the specified flow-rate coefficients, respectively. The unsteady pressure fields were computed for the circumferential harmonic incoming gust with the coordinate system fixed on the fan using k-e turbulance model. For circumferential harmonic gusts, acoustic spectrum computed from quazi-steady numerical solution is composed of pure tones which are integer multiples of the rotation frequency and compared with the experimental results. To control the tonal components, wavy-walled inlet guide was deliberately designed and tested numerically under the forementioned non-uniform inflow conditions. In this study, the design method of wavy-walled inlet guide and the computed pressure modulations are seen. The tonal components of sound energy are suppressed and redistributed into broadband components with the wavy-walled inlet guide applied to non-uniform incoming flows.