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DYNAMIC MODES IN TURBULENT CAVITY FLOWS CAUSING SELF-SUSTAINED OSCILLATIONS

Abu Seena
Department of Mechanical Engineering, KAIST 291 Daehak-ro, Yuseong-gu, Daejeon, 305-701, South Korea

Hyung Jin Sung
Department of Mechanical Engineering, KAIST 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Korea

Résumé

Large eddy and direct numerical simulations of incompressible turbulent flows were performed over an open cavity with or without self-sustained oscillations possessing thin or thick incoming boundary layers (ReD = 12000 and 3000). The influence of the incoming turbulent boundary layer on the cavity was investigated using dynamic mode decomposition (DMD). The cavity length to depth ratio of 2 was selected for both cases. In the case of thick boundary layer, the dynamic modes extracted using the DMD algorithm shows that the upcoming boundary layer structures and the structures generated due to the shear layer oscillations differs in wavelength space. The upcoming BL structures larger than the cavity dimensions convect over the cavity. On the other hand, in the case of thin boundary layer both of the upcoming and the shear layer structures possess comparable dimensions. This may lead to the condition of resonance causing self-sustained oscillations. This result suggests that the hydrodynamic resonance causing self-sustained oscillations occur when the upcoming boundary layer structures and shear layer structures coincide both in the frequency and wavenumber space. The structures of the cavity perturbations change with the cavity size and upcoming momentum thickness.