Effects of inflow turbulence and slope on turbulent boundary layer over two-dimensional hills

The characteristics of turbulent boundary layers over hilly terrain depend strongly on the hill slope and upstream condition, especially inflow turbulence. Numerical simulations are carried out to investigate the neutrally stratified turbulent boundary layer over two-dimensional hills. Two kinds of hill shape, a steep one with stable separation and a low one without stable separation, and two kinds of inflow condition, laminar and turbulent, are considered. An auxiliary simulation, based on the local differential quadrature method and the recycling technique, is performed to simulate the inflow turbulence to be imposed at the inlet boundary of the simulation with turbulent inflow, which preserves very well in the computational domain. A large separation bubble is established on the leeside of the steep hill with laminar inflow, while the reattachment point moves upstream under turbulent inflow condition. There is stable separation on the lee side of the low hill with laminar inflow, while not with turbulent inflow. Besides increase of turbulence intensity, inflow turbulence can efficiently enhance the speedup around hills.So in practice, it is unreasonable to study wind flow over hilly terrain without considering inflow turbulence.