Numerical Investigation of Active Flow Control using Steady Blowing for Landing Gear Noise Reduction

Abstract

Active Flow Control in the form of steady blowing is used with the aim of reducing the noise generated by high Reynolds number flow over bluff bodies. A Computational Fluid Dynamics solver is used to compute the flow field and provide surface pressure samples to a Ffowcs Williams-Hawkings solver to obtain far-field acoustic pressure signals. Two geometries are considered, a circular cylinder and a main strut and drag-stay configuration with the upstream drag-stay inclined by 25◦ towards the upstream direction. The latter is representative of interaction flow occurring in a landing gear. The steady blowing is applied on the cylinder and drag-stay configurations from a slot located on both sides of the body at ±30◦, measured from the stagnation line. For the drag-stay configuration, blowing at 180◦ is also investigated. In the isolated cylinder configuration, the noise reduction obtained by blowing at ±30◦ is found to be related to a modification of the flow field directly downstream of the cylinder. An increase in the recirculation region length and a reduction of the velocity fluctuations are observed. However, applying the same flow control on the drag-stay configuration results in an increase in the overall noise. Blowing at 180◦ on the drag-stay component results in a maximum reduction of 8.5 dB at the shedding peak frequency for an observer aligned with the lift dipole to the side of the drag-stay configuration. The self-noise of both components and the interaction noise are reduced.