Noise Reduction of Open Cavities by Passive Flow Control Methods at Transonic Speeds using OpenFOAM
Flow over a cavity is one of the most intriguing problems in the field of aeronautics. Even though the geometry is simple, the physics behind the cavity requires uttermost attention and detailed investigation. In this study, various novel passive flow control techniques such as reshaping the cavity aft wall in a stair-stepped configuration or combination of spoilers with reshaped cavity aft wall as a combined method are applied to cavity and effects of these techniques are investigated numerically in detail. Combined configurations of aft wall reshaping and spoiler to fore of the cavity that are proposed in the present study are novel and have a potential to contribute to the literature. Analyses are performed with Detached Eddy Simulation (DES) method three-dimensionally in transonic regime (0.85 Mach) for a Reynolds number of ~107 based on the cavity length, 0.508 m, using the open-source software OpenFOAM. Results are compared with both experimental data and each other, fundamentally in terms of Overall Average Sound Pressure Level (OASPL). Further examinations are also performed for features such as Mach number, turbulent intensity and turbulent coherent structures. It is seen that combined passive flow control methods have reduced OASPL ~10 dB. Newly proposed passive flow control methods have also reduced OASPL by ~6 dB. A high correlation between coherent turbulent structures and generated noise is observed.
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