The Use of Porous Meshes to Reduce Landing Gear Wake - Flap Interaction Noise

This work investigates the use of porous meshes to reduce the interaction noise between a generic two-wheel main landing gear and a downstream wing. This is a simplified representation of landing gear wake - flap interaction noise assuming the primary mechanism is leading edge noise from the flap. Acoustic and hot-wire measurements were performed at the Anechoic Wind Tunnel (AWT) at the University of Southampton. Microphones where located in a flyover arc as well as a lateral sideline direction. Hot-wire measurements were taken at several positions and velocities downstream of the landing gear at a three different spanwise positions. Porous screens made from woven meshes and perforated plates, with different values of porosity, are installed at several streamwise locations between the landing gear and the wing, and tested at different Reynolds numbers. Hot-wire measurements were acquired to characterise the turbulent wake downstream of the landing gear and the screens at the streamwise location of the leading edge of the wing. The purpose of this study is to optimise two variables; the porosity of the fairing and the streamwise distance the fairing is placed downstream of the landing gear, in order to minimise the interaction noise between the landing gear and the wing. The radiated noise was the main way to assess the acoustic effect of installing porous screens downstream of a landing gear. Hot-wire measurements were used to link the changes in farfield noise to changes in the turbulent characteristics of the wake downstream of the porous meshes. The optimum porous mesh for reducing the leading edge noise was found to be a woven mesh with an open area of 60%. The reason was found to be a balance between reducing the wake convection velocity that impinged on the flap with a minimum increase in the turbulent intensity due the introduction of the mesh and reduced turbulent generation around the frame edge with the woven mesh installed. The optimum location was found to just after the landing gear although the variations with streamwise position were a much smaller effect than the porosity of the mesh.