Direct numerical simulation of the turbulent boundary layer over a bump with relaminarization*

The turbulent boundary layer over the two-dimensional Gaussian-shaped Boeing bump is computed by direct numerical simulation of the incompressible Navier–Stokes equations. At the inflow, the momentum thickness Reynolds number is approximately 1000 and the boundary layer thickness is 1/8 of the bump height. Results show that the strong favorable pressure gradient (FPG) on the upstream side of the bump causes the boundary layer to enter a partial relaminarization process, with the near-wall turbulence being significantly weakened and becoming intermittent. At the bump peak, where the FPG switches to an adverse pressure gradient (APG), the near-wall turbulence is suddenly enhanced through a partial retransition process which energizes the internal layer, making it more resilient to the strong APG. In the strong FPG and APG regions over the bump, the inner and outer layers become largely independent of each other. The near-wall region responds to the pressure gradients and determines the skin friction, whereas the outer layer behaves similarly to a free shear layer subject to pressure gradients and mean streamline curvature effects.