Aeroacoustic Comparison of Airfoil Leading Edge High-Lift Geometries and Supports

Abstract

*† ‡ Slat noise originates due to unsteady flow within the slat cove and in the trailing edge wake of the slat. An aeroacoustic study was conducted in the 5½-by-4-foot Cambridge University Markham wind tunnel in order to further understand and treat slat noise. A twopart wing and slat model was used for this research. Separate low and high frequency phased microphone arrays consisting of 48 channels each were used to determine the source strengths associated with the noise within the slat cove. The aerodynamic forces on the models were determined separately using a three component overhead force-balance. Modifications to the airfoil geometry were made in order to analyze their effectiveness in reducing the overall leading edge noise. The alterations reported here are filling in the slat cove and drooping the leading edge geometry. The slat brackets were identified as significant contributors to the cumulative noise from the slat region and thus a supplementary study on a simple plate bracket, a cylindrical and an I-beam shaped bracket. The models were tested at angles of attack from six to sixteen degrees, and 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 source of noise. A drooped profile is successful in removing the slat noise with a small reduction in aerodynamic performance. 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. The force balance results show that, after filling in the slat cove, the model stalls prematurely. Thus, for modifications reported here, any acoustic benefits are likely to be accompanied by aerodynamic performance penalties. The I-beam supports induce a greater acoustic intensity than a cylindrical support, and both are noisier than a plate support. Additionally, the contribution to the overall noise in the slat region, from supports, is greater at the lower freestream velocities.