Adaptive Wall-Modeling Strategy for Large-Eddy Simulation of Nonequilibrium Turbulent Flows

To improve the accuracy of an equilibrium (EQ) wall-stress model in strongly nonequilibrium (NEQ) turbulent boundary-layer flows, an adaptive strategy is proposed to determine the optimal modeling interface (also known as the exchange location, the matching location, etc.) from several candidates spanning a range of heights. First, with a new NEQ sensor, the flows are instantaneously categorized as quasi-EQ and NEQ types. For quasi-EQ turbulent flows, the interface is placed at 10–20% of the local boundary-layer thickness away from the wall, with at least two solution points underneath to ensure the accuracy of the large-eddy simulation (LES) input. For NEQ turbulent flows with significant pressure gradients and separation, we propose using an optimal interface that minimizes the local NEQ effect within the underlying inner layer, while ensuring that the wall-shear-stress direction remains aligned with that predicted using the specified innermost interface. The local NEQ effect is evaluated by integrating a moving-time-averaged streamwise pressure gradient from the wall to the interface. Two benchmark NEQ turbulent flows over a periodic hill and a smooth ramp are calculated for verification. Our numerical experiments show that the proposed approach is a practical way to improve the simulation accuracy of strongly NEQ turbulent flows with EQ stress-based wall-modeled LES.