Large-eddy simulation and analysis of non-equilibrium turbulent boundary layers

Evolution of a turbulent boundary layer (TBL) under streamwise varying pressure gradient conditions is studied using wall-resolved large-eddy simulation (LES). The simulations are based on the experiments of Volino (Journal of Fluid Mechanics 897, A2, 2020), who performed profile measurements at several streamwise stations in an initially zero pressure gradient TBL evolving through a region of favorable pressure gradient, followed by a zero pressure gradient recovery and a subsequent adverse pressure gradient region. The pressure gradient quantified by the acceleration parameter was held constant in each of these three regions. The simulation setup and the computational grid are carefully designed to mimic the experimental conditions without requiring a long development region for the incoming zero pressure gradient TBL. The computational grid is able to resolve the rapid thinning and thickening of the TBL in the favorable and adverse pressure gradient regions respectively. The LES results show good agreement with the experimental data at several stations in the domain. The results are analyzed to understand the behavior of non-equilibrium TBL, which are common in many engineering applications.