Leading-edge Serrations for Noise Control from Tandem Airfoil Configuration

This paper presents an experimental study on passive noise control for a tandem NACA65-710 airfoil configuration by applying serrations to the leading edge of the rear airfoil. A comprehensive study has been performed for different airfoil gap distances, angles of attack and velocities. Wake-profile measurements on an isolated airfoil are used to determine the maximum turbulence intensity locations for the optimal positioning of the rear airfoil for near-field and far-field acoustic measurements. The far-field noise measurements and noise directivity analysis have demonstrated that the use of leading-edge serrations can lead to significant noise reduction from the tandem airfoil configuration. The near-field hydrodynamic analysis obtained using remote-sensing of the fluctuating pressure field overthe airfoil has shown that the use of leading-edge serrations causes significant reduction in the unsteady aerodynamic load acting on the airfoil, particularly along the serration tip plane. This is believed to be due to a strong flow separation from the serration tip region. Further hydrodynamic field and near-field to far-field coherence investigations are planned to better understand the mechanisms leading to the reduction of the far-field noise.