Flow Topology and Noise Sources of a Deflected Spoiler Mounted to a Flat Plate

During a steep descent, spoilers can be deployed as part of noise abatement procedures to reduce the approach velocity of an aircraft. Once deployed, the spoiler induces changes in the circulation of the high-lift wing, leading to changes in slat and flap noise sources, as well as introducing its own additional sources. In order to separate these effects, a spoiler mounted to a flat plate is studied to investigate the noise sources solely due to the spoiler. The flow topology of this geometry and the corresponding noise sources are determined from numerical simulations. Numerical simulations are conducted using ProLB(TM) for this simplified model at a deflection angle of 30°. These simulations are validated with experimental data for the same geometry and deflection angle. The experimental data includes aerodynamic loads, far-field noise, on-surface pressure distributions, hot wire anemometry and particle image velocimetry. Good agreement was observed between the experimental and numerical results in terms of predicting the main flow features. The flow is characterised by a bluff body broadband wake with no coherent vortex shedding. While both experiments and numerical simulations predicted the presence of an upstream separation bubble, there were some differences in its location. The flow topology of a wall-mounted spoiler is observed to be defined by a horseshoe separation vortex forming upstream of the hinge of the spoiler, a broadband wake, and two ground edge vortices that are attached to the base plate. Both the horseshoe vortex and the ground edge vortices cause high on-surface pressure fluctuations, making them the primary noise sources for the deflected spoiler.