Prediction of Rotorcraft Broadband Trailing-Edge Noise and Parameter Sensitivity Study

This paper investigates effects of rotorcraft design and operating parameters on its trailing-edge noise. A rotor trailing-edge noise prediction method is first developed, where the aerodynamics and the turbulence wall pressure spectrum near the trailing edge on airfoils are predicted by a combination of the standard blade element momentum theory (BEMT), a viscous boundary-layer panel method, and a recently developed empirical wall pressure spectrum model. The coordinate transformations are combined with the Amiet model to predict far-field noise. Compared to experimental data, the validation of this method demonstrates its advantage and validity for airfoil and rotorcraft broadband noise predictions. Thereafter, this method is used to study effects of rotorcraft design and operating parameters on rotor trailing-edge noise. It is found that the tip Mach number is a dominant factor for rotor trailing-edge noise. It is found that the broadband noise scales with the 5.5th power of the rotor tip Mach number. Detailed trend analyses of noise levels as a function of frequency are presented in terms of collective pitch angle, twist angle, blade chord length, and rotor radius. It is found that the collective pitch angle, twist angle, and the chord length make noticeable impacts on the low- and mid-frequency noise. A dipole noise directivity is observed, and the directivity and geometric attenuation of rotor trailing-edge noise can be well represented by a semi-analytic equation.