Experimental Investigation of Jet-Flap-Interaction Noise Sensitivity due to varying flap parameters at a UHBR Engine/High-Lift-Wing installation

Abstract

Since Jet-Flap-Interaction (JFI) has the potential to become a relevant noise source, especially in high-lift-related operations such as approach and takeoff, a fundamental understanding of influencing key parameters helps to quantify noise levels and help facilitate finding noise reduction measures. This paper is about a windtunnel study which was conducted at a DLR facility, the Aeroacoustic Windtunnel Braunschweig (AWB), and which was partnered with Airbus. A 6" UHBR engine (area ratio 8) is mounted to a straight high-lift-wing (DLR-F16), whereby the study concentrates on installation parameters, showing effects of slight changes around typical operational points. The main focus is a study on flap settings, i.e. flap deflection angle, overlap, and gap settings as well as a comparison to vertical wing-engine-positioning. While DLR analysed and assessed the aeroacoustic data, aerodynamic data was evaluated by Airbus. For each build change, microphone data is used to show changes in SPL and directivity. Acoustic noise source maps are obtained using a beamforming technique. For mid and high Strouhal numbers, the noise maps show mainly two sources, whereby one of them contains the JFI Noise. For this mid to high frequency range, the sources are spatially seperated. This method allows to evaluate the signal composition per datapoint as well as changes in the spatial noise source region due to build changes. All of those evaluations show how sensitive JFI noise is to vertically diminishing distance between engine axis and flap trailing edge and how comparingly insensitive slight horizontal changes between engine outlet and flap trailing edge are. In order to find a general acoustic model, characteristic velocities and geometrical parameters were investigated. Aerodynamic data of jet normal planes was obtained experimentally using a five hole rake. A method to identify key characteristic jet parameters by velocity is proposed and successfully tested against the vorticity field. The transformation of the jet shape from circular, to a wing-fitted rectangular top and the butterfly-like downstream flow is portrayed. JFI SPL scaling has been attempted for characteristic velocities.