Airfoil Trailing-Edge Blowing: Broadband Noise Prediction from Large-Eddy Simulation

In recent studies, trailing-edge blowing has been found to be a potential technique for broadband noise reduction in turbomachinery applications with rotor-stator arrangement. The primary idea involves injecting fluid into the wake of the rotor such that the wake becomes momentumless, and the turbulence structure is modified by the enhanced mixing process. This wake manipulation should lead to a reduced aeroacoustic response of the downstream stator vane with the modified turbulent wake of the rotor. This study investigates the trailing-edge blowing mechanism by numerical means in a simplified configuration. A large-eddy simulation of a single NACA 6512-63 airfoil at a low Mach number with trailing-edge blowing is undertaken to investigate the effect of blowing on wall-pressure statistics of the blowing airfoil and also on its wake turbulence structure. The broadband self-noise and the wake-airfoil interaction noise are predicted from the simulation using Amiet's edge noise theories. It appears that two competing mechanisms exist: an increased airfoil self-noise for frequencies above 2 kHz due to the blowing jet interacting with the trailing edge and a reduction in wake-airfoil interaction noise for frequencies below 2 kHz through wake turbulence reduction. The predictions compare well to microphone measurements from wind-tunnel experiments.