Design of the centrifugal fan of a belt-driven starter generator with reduced flow noise

Abstract

Abstract Large eddy simulations based on the explicit algebraic subgrid-scale stress model were carried out to predict the flow-induced noise generated on the centrifugal fan of a belt-driven starter generator using Lighthill s analogy and the method of Ffowcs Williams and Hawkings. The surrounding air was approximated by an ideal gas at fixed room temperature (Tin\xa0=\xa0300\u202fK), and the rotating velocity of the fan was considered to be 6000\u202frpm. The blade array angles were designed using the modulation method, and a large blade curvature was adopted. We identified several centrifugal fan design parameters that could minimize the flow-induced noise while also minimizing fan efficiency losses. Three design parameters: the top serrated edge (θt), the step leading edge (0.52 Hb) and the tail edge (db and rb), played a critical role in preventing vortex generation and collision, significantly weakening the surface pressure fluctuations on the blade. The maximum sound pressure level at 800\u202fHz at a specific location was reduced by 5.5\u202fdB (at the top serrated edge) and 6.8\u202fdB (at the step leading edge) relative to the baseline case. The sound power, calculated over a hemisphere surface of 950\u202fmm, was reduced by 77.3% (at the top serrated edge) and 61.0% (at the step leading edge) relative to the baseline whereas the mass flow rates were reduced by 5.2% and 10.6%, respectively. Experiments were performed using the optimally designed fan in a semi-anechoic chamber. The predicted sound pressure level and frequency were in good agreement with the experimentally measured values.