On the Application of Trailing-edge Serrations for Noise Control from Tandem Airfoil Configurations

This paper presents a preliminary study on the application of serrations as a passive control method for reducing the aerodynamic sound from airfoils in tandem. The aim of the study is to investigate the effectiveness of serrated trailing-edge on cambered NACA 65-710 tandem airfoil to control and regularize the turbulent flow within the gap area between the two airfoils. The wake flow characteristics for a cambered NACA 65-710 airfoil with and without the serration treatment have been quantified using two-dimensional Particle Image Velocimetry (PIV). To better understand the aerodynamic and aeroacoustics effects of serrations on the tandem configuration, the rear airfoil was equipped with several pressure taps and surface pressure transducers. The surface pressure coefficient distributions and surface pressure fluctuations have been measured using the pressure taps and remote sensing probe technique. Experiments were performed using a sharp sawtooth serration, for a number of tandem airfoil configurations, with different airfoil separation distances. The results show that the use of serrations at relatively high angles of attack, namely 10 and 15 degree, can lead to a significant reduction of the turbulent kinetic energy, which is believed to be due to the interaction between the flow field at the tip and root of the serrations. Results have also shown that a significant reduction of surface pressure fluctuation can be achieved over the leading-edge area of the rear airfoil, particularly for configurations at high angles of attack. The wake and surface pressure results have confirmed that the use of serrated trailing-edges can lead to robust control of the wake flow and reduction of wake interaction noise.