Outer layer turbulence dynamics in a high-Reynolds-number boundary layer up to recovering from mild separation

The outer layer dynamics of a high-Reynolds-number boundary recovering from non-equilibrium is studied utilising the multi-resolution approach zonal detached eddy simulation mode 3. conditions are obtained separation over rounded step enhancing turbulent production, and recovery happens during redevelopment after reattachment at high Reynolds numbers ( $Re_{\theta,max}\approx 24{,}000$ ). Most turbulence resolved by simulation, which reproduces accurately experimental relaxation. spectral analysis streamwise velocity fluctuations kinetic energy (TKE) production evidences different content distribution within region, very large-scale motions identified with wavelengths up to $\lambda _x = 9\delta$ , where $\delta$ thickness. analysed in terms persistence secondary peak TKE evolution wall-shear stress statistics. skewness probability density function skin friction show slower relaxation than downstream flow fraction. This confirms long-lasting impact perturbations wall-bounded flows. persistent state suggested be reason for reported lack accuracy considered Reynolds-averaged Navier–Stokes models region.