DNS-BASED ADJOINT OPTIMIZATION OF THE WALL SHAPE IN TURBULENT CHANNEL FLOW

Kurzfassung

Direct Numerical Simulations (DNS) of turbulent channel flow are performed in a computaional domain and for the friction Reynolds number Reτ = 180 realized by Kim with the aim to reduce the skin friction by controlling the near- wall transport processes based on surface modifications. The latter are determined by solving the adjoint Navier-Stokes equations which depend on time-averaged DNS flow fields. It is well known that the wall-normal momentum Transport is organized in sweep and ejection events in the boundary layer which controls skin friction. Bewley et al. used adjoint optimization for suction and blowing in turbulent channel flow. They mitigated the effect of the wall-normal transport by opposing near-wall vertical motions of the fluid with an equal and opposite control velocity at the wall. The aim of this work is to achieve this with wall surface modifications. The idea is further to damp the spanwise fluctuations of streaky structures and thus, to reduce the associated skin friction.