Panel methods for airfoils in turbulent flow

This paper describes how panel methods can be used to calculate the unsteady loading and radiated noise from airfoils in incompressible turbulent flow, while completely accounting for the mean flow distortion of the turbulence in the vicinity of the blade. Formulations based on the velocity and on the stagnation enthalpy are discussed. In three-dimensional flows, care must be taken with the velocity-based formulation to avoid singular behavior associated with vortex stretching by the mean flow. The velocity-based method is implemented in two dimensions to illustrate application of these methods, and is validated against Amiet's theory. Calculations showing the effect of blade thickness and angle of attack on the unsteady loading spectra are given. It is concluded that airfoil angle of attack has only a small effect on the unsteady loading, but that blade thickness reduces the spectral levels at high frequencies.