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GENERALISED OPTIMAL PERTURBATION APPROACH APPLIED TO DRAG REDUCTION BY WALL OSCILLATIONS IN TURBULENT FLOWS

Olivier Blesbois
Department of Aeronautics Imperial College London Prince Consort Rd., London SW7 2AZ

Sergei I. Chernyshenko
Department of Aeronautics Imperial College London Prince Consort Rd., London SW7 2AZ

Аннотация

Drag reduction by wall oscillations in turbulent flows has recently been shown to be a promising technique. The reduction of the near wall streaks amplitude is known to play a significant role in the drag reduction mechanism. To gain a better understanding of the effect of wall oscillations on the streaks, the Generalised Optimal Perturbation (GOP) approach, based on the linearised Navier-Stokes equation, is used. Resemblance between drag and certain quantities arising in the GOP context is observed. It is found that for harmonic wall oscillations the streaks have an approximately constant angle to the main flow direction, with a jump in sign twice in the period. The mechanism of this phenomenon is clarified. The results are in a reasonable agreement with direct numerical simulations.