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

Abstract

This paper investigates the effects of rotorcraft design and operating parameters on 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 , 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 advantages and validity for airfoil and rotorcraft broadband noise predictions. Then, this method is used to study the effects of rotorcraft design and operating parameters on rotor trailing-edge noise. It is found that helicopter broadband noise scales with the 4.5th to 5.0th power of the tip Mach number in which the range is determined by the typical helicopter collective pitch angle in operation. Detailed trend analyses of noise levels as a function of frequency are presented in terms of the collective pitch angle, twist angle, rotor solidity, rotor radius, disk loading, and number of blades. It is found that the collective pitch angle, twist angle, and chord length make noticeable impacts on low- and midfrequency noise. Finally, a semianalytic model is presented to predict the directivity and geometric attenuation of rotor trailing-edge noise.