Modeling centrifugal fan blade trailing edge noise

Centrifugal fan noise contains numerous aeroacoustic mechanisms, one of them being trailing edge noise due to turbulent boundary layer flows convecting over the blade trailing edge. A fundamental research program was conducted to develop a trailing edge noise database and assess the ability of existing aeroacoustic models to predict this mechanism. The database included unsteady surface pressure spectra, trailing edge wake characteristics, and acoustic sound power. To focus on trailing edge noise, a mixed flow radial fan was simulated with a circumferential array of nonrotating vanes located in a radial diffuser. Both loaded and unloaded vane geometries were tested to simulate varying pressure gradients in an actual fan blade passage. It was demonstrated that the trailing edge noise mechanism can be accurately predicted if the trailing edge wall pressure spectrum is known a priori. However, for radial fans the strong adverse pressure gradients appear to rule out the existence of a ‘‘universal’’ wall spectrum shape typically observed in flat plate zero pressure gradient boundary layer flows. Hence, futher trailing edge noise modeling needs to focus on predicting surface pressure spectrum shape, in addition to, amplitude and frequency content.