Aeroacoustic Study of Airfoil Leading Edge High-Lift Devices

Abstract

The aim of this research is to attempt to mitigate the sources of noise in the leading-edge slat region without compromising performance or safety. Noise from the slat originates due to unsteady flow within the slat cove and in the tr ailing edge wake of the slat. In order to further understand and treat these sources, an aero acoustic study was conducted in the 5Ωby-4-foot Cambridge University Markham wind tunnel. The study was carried out using a two-part wing and slat model that spanned the tunnel horizontally. Separate low and high frequency phased microphone arrays consisting of 48 channels each were used to determine the source strengths associated with the noise with in the slat cove. The aerodynamic forces on the model were determined from separately-conducted overhead balance measurements. Modifications to the slat geometry were made in order to analyse their effectiveness in reducing the slat noise source str engths. The alterations reported here are taping over the upper surface gap and filling in th e slat cove region. The models were tested at angles of attack from six to sixteen degrees, an d at flow speeds of 20, 30, and 40 m/s. Boundary layer trips were used to simulate the full -scale, high Reynolds number flow. The tests confirmed that the slat is a significant sour ce of noise. A sealed slat gap is very effective at reducing the noise, but limits the aerodynamic p erformance. A filled cove on the other hand reduces the sources of noise by a few decibels . However, the concept is less effective than hoped due to the enhancement of other sources of noise. Also, the force balance results show that, after filling in the slat cove, the mode l stalls prematurely. Thus, for modifications reported here, any acoustic benefits are likely to be accompanied by aerodynamic performance penalties.