Trailing-Edge Noise Predictions of Rotorcraft Airfoils

Abstract

This paper presents the effect of rotorcraft airfoils on turbulent boundary layer trailing-edge noise. Among the numerous airfoils available for rotocraft application, a total of eleven commonly used airfoils are selected and divided in three groups, and their corresponding trailing-edge noise is investigated. The compressible Reynolds Averaged Navier-Stokes (RANS) CFD simulation coupled with a semi-empirical wall pressure spectrum model and a physics-based far-field noise prediction theory is used to predict noise levels at varying angles of attack. In this paper, the CFD tools and the noise prediction model are first validated, and then the trailing-edge noise analyses for the eleven airfoils under the same compressible flow condition are presented. It is found that NACA 0012, VR-12, and SC-1094 R8 airfoils show low trailing-edge noise levels compared to other similar airfoils in each group. The noise characteristics from airfoils like NACA 0012 shows clear separation in the frequency range where the noise from the suction or pressure side is dominant at low and high frequencies, respectively. However, airfoils like VR-12 shows that the suction-side trailing-edge noise can still be important at high frequency at small angles of attack, thus producing a combined effect from both suction and pressure sides. Furthermore, a natural laminar flow airfoil is considered to investigate how the trailing-edge noise responds to the delayed transition locations. It is observed that the delayed transition locations reduce the low- and high frequency noise at a higher angle of attack.