Adjoint shape optimization based on DNS of turbulent channel flow

Abstract eng:
Direct Numerical Simulations (DNS) of turbulent channel flow are performed with the aim to reduce the skin friction by controlling the near-wall transport processes based on surface modifications. The latter are determined based on the solution of the adjoint Navier-Stokes equations which provides surface sensitivities indicating an optimal wall shape. With the modified geometry the DNS is continued until a new fully developed state is reached. Time-averaging of the instantaneous wall shapes produced with this approach will finally lead to a steady wall shape which controls the flow according to a prescribed objective function. Considering that the objective function turbulence kinetic energy (TKE) is minimized, the approach produced a reduction of ≈ 9.3% and a mean pressure gradient, required to drive the flow, which is reduced by ≈ 7.5%. Currently, different objective functions are tested to identify flow parameters which are suitable to effectively reduce the skin friction in turbulent channel flow.

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