A COMPUTATIONAL STUDY OF THE AEROACOUSTICS OF ROTORS IN HOVER

The noise from low-thrusting rotors in hover is examined for a wine ra nge of tip Mach numbers for various blade planforms using several diff erent methods. The first approach is to use an Euler/Navier-Stokes cod e to calculate the acoustic field without using any acoustic analogy t o examine the wavefront formation process and acoustic propagation thr ough a nonlinear flowfield. Furthermore, the near field solutions from the CFD code are used as input to two different methods: a code based on the linear stationary Kirchhoff formulation and a code based on th e linear acoustic analogy approach. The results from the CFD code comp are very well with the experimental acoustic data available, as do the results from the Kirchhoff code. However, the lack of quadrupole term s in the linear acoustic analogy approach causes the negative peak pre ssure to be underpredicted by a factor of two in-plane at high tip spe eds. This underprediction decreases as an observer moves out-of-plane. Finally, the CFD code is used to study the acoustic field for five di fferent rotor blades, This study provides useful insight into the nois e generating mechanisms of various blade planform shapes and near fiel d wavefront formations near the blade.