Efficient Methodology with Grid Configurations for HSI Noise Prediction in Hover

Abstract

Complex and unsteady flow patterns occur around rotating rotor blades owing to the generation of shock waves at the blade tip and interference between the blade and tip wake when the blade rotates at high speeds, thereby resulting in specific noise characteristics. Furthermore, these noise characteristics cause noise pollution in private areas and degrade detectability of helicopters in military applications. Therefore, it is important to accurately analyze noise characteristics around rotor blades. In this study, a novel computational methodology with a chimera wake grid was proposed to efficiently and accurately predict high-speed impulsive (HSI) noise due to the shock wave at the blade tip. The proposed method enables accurate analysis of a complex flow region by overlapping a wake grid in the vicinity of shock waves. A 1/7-scaled UH-1H rotor blade was used to compare and verify the accuracy of HSI noise prediction and computational efficiency. The chimera grid method was applied to the present simulation for considering the blade motion and moving effects. A permeable surface for wrapping the surface of the physical blade was constructed to include quadrupole noise source generated from the control volume, thickness noise source, and loading noise source. Furthermore, the permeable Ffowcs Williams and Hawkings (FW–H) equations were used with the Kirchhoff approach to realize efficient far-field noise prediction. The proposed HSI noise analysis via chimera wake grid indicated that the strength of the shock wave is more precisely predicted, thereby resulting in improved prediction of the HSI noise. The proposed chimera methodology allows efficient noise prediction using a much coarser background grid system.