Wall-resolved large-eddy simulation of non-equilibrium turbulent boundary layers

Evolution of a turbulent boundary layer (TBL) under a streamwise varying pressure gradient 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 profiles of mean velocity and Reynolds shear stress components obtained from LES show good agreement with the available experimental data at several stations in the domain. The response of TBL to changing pressure gradients is analyzed to understand the behavior of non-equilibrium TBL, common in many engineering applications.