A computational study of the aeroacoustics of rotors in Hover

The noise from low-thrusting rotors in hover is examined for a wine range of tip Mach numbers for various blade planforms using several different methods. The first approach is to use an Euler/Navier-Stokes code to calculate the acoustic field without using any acoustic analogy to examine the wavefront formation process and acoustic propagation through 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 the linear acoustic analogy approach. The results from the CFD code compare very well with the experimental acoustic data available, as do the results from the Kirchhoff code. However, the lack of quadrupole terms in the linear acoustic analogy approach causes the negative peak pressure to be underpredicted by a factor of two in-plane at high tip speeds. This underprediction decreases as an observer moves out-of-plane. Finally, the CFD code is used to study the acoustic field for five different rotor blades, This study provides useful insight into the noise generating mechanisms of various blade planform shapes and near field wavefront formations near the blade.