Broadband Trailing-Edge Noise Prediction of a Four-Bladed Axial Fan using a Semi-Analytical Method

G2 - Prediction of Axial Fan Noise by Hybrid Methods (ii)

The trailing-edge noise is the minimum broadband sound that a lifting surface would produce in absence of other sound mechanisms as turbulence interaction at the leading edge. This source of sound, caused by the scattering of the boundary-layer disturbances into acoustic waves, remains the only broadband noise contributor for subsonic fans operating in homogeneous stationary flows, in absence of any upstream, downstream and tip interaction. The present study aims at predicting the trailing-edge noise of a four-bladed low-speed axial fan on which an experimental campaign has been conducted at CETIAT. The available experimental database is shared in a collaborative project including VKI, CETIAT and CETIM, for development and validation of numerical flow and noise prediction methods.
In the present work, the flow and acoustic prediction is based on methods keeping balance between cost and accuracy that can be easily integrated in optimization chains. The procedure uses stationary flow computation and semi-analytical Amiet’s theory. The flow is first solved using OpenFOAM, where a 3D steady RANS computation is performed using a Multiple Reference Frame method. The wall-pressure spectrum upstream the trailing-edge required in the trailing-edge noise theory is then obtained from a wall-pressure reconstruction model of Panton and Linebarger using boundary-layer information. Finally, the far-field sound pressure spectrum is computed by means of Amiet’s theory. The blade is decomposed using a strip theory where every blade strip is approximated by a rectangular flat plate, the overall noise radiated from the blade being the sum of noise radiated from the different blade strips. The sound produced by the tip vortex and its possible interaction with the shroud is neglected in the present study.
Comparisons with experimental available data is made for the different steps of the noise prediction procedure. The flow is validated in terms of global fan performances available experimentally. The wall-pressure reconstruction spectra is compared to measured wall-pressure spectra at two locations on the suction side of the blade while the sound emitted from the fan is compared to overall sound measured in the CETIAT reverberant room.