Effect of the load coefficient on the aerodynamic noise of a high-bypass-ratio fan by a numerical approach

The fan is one of the main aerodynamic noise sources in a high-bypass-ratio turbofan engine. It is easy to reduce the rotating speed of a geared fan by increasing the reduction ratio of the gear without changing the original structure of the turbofan engine. In this paper, the effect of the load coefficient on the geared fan aerodynamic noise was investigated, where the load coefficient was varied by changing the fan rotating speed. The acoustic fields of three fans were simulated by a combination of unsteady flow field calculation using ANSYS CFX and acoustic BEM calculation using LMS Virtual Lab. software. The main results are as follows. For the rotor alone, the tonal noise and broadband noise dramatically decrease when the load coefficient increases with a decrease in rotating speed, and the acoustic power level of the fan stage also decreases because of the decrease in rotor rotating speed. In particular, for the ultra-highly loaded fan stage (load coefficient 0.88), both noise and aerodynamic performance are better than those for the fan stage with normal load (load coefficient 0.3), the acoustic power of the fan stage is decreased by 11.71 dBA, the efficiency is increased by 0.012 and the surge margin is increased by 28.5%.