Numerical investigation on accelerating boundary layer subject to strong free-stream turbulence and Görtler instability

This research is based on the highly resolved large-eddy simulation database of a high-pressure turbine vane (Zhao & Sandberg, J. Fluid Mech., 2020), focusing on the boundary layer on the pressure side of the turbine blade, which is subject to combined effects of strong favorable pressure gradient (FPG), free-stream turbulence (FST) and Görtler instability due to the concave wall. On the one hand, the time- and spanwise-averaged flow remains laminar under the stabilizing effect of the FPG. The self-similar velocity boundary layer can be well described by the Falker-Skan equation, with a good estimation of the wall friction coefficient. On the other hand, the velocity fluctuation in the boundary layer is initially inhibited by the strong FPG while then amplifying significantly further downstream. The growth of the velocity fluctuation is presumably caused by the Görtler instability, as the Görtler number gradually increases and starts to play a leading role. In addition, small-scale vortices form in the near-wall region, inducing mushroom-like structures that spring up from the wall. The intense wall-normal transport caused by the vortical structures significantly enhances the heat flux to the wall.