Comparison of Rotor Noise Predictions by a Lifting Surface Method and Euler Solutions Using Kirchhoff Equation.

Abstract

Computational results of two acoustic methods, a linear and an Euler/Kirchhoff method used at DLR are compared against each other and with hovering rotor test results. The considered rotors are models of the BO-105 and UH-1H helicopter. In order to check the dependency of the acoustic prediction on linear and non-linear calculated aerodynamic input data, a subsonic BO-105 test case was investigated. Here the aerodynamic calculations were performed with a Lifting Surface and 3D-Euler Code. All calculated acoustic loading and thickness noise contributions are underpredicted compared with experimental results. The complete linear calculation of aerodynamics and acoustics (Lifting Surface Code LBS/Farassat formulation 1) compared with Euler/Farassat formulation 1 and Euler/Kirchhoff calculations show an acceptable agreement. For tip Mach numbers from 0.85 to 0.95 linear and non-linear computed acoustic signatures were compared with test results.