Evaluation of an optimal slip wall model for large-eddy simulation*

The slip wall model for large-eddy simulation of wall-bounded turbulent flows is derived from application of a specific filtration to the Navier-Stokes equations (Bose & Moin 2014; Bae et al. 2019). This is in contrast to traditional equilibrium wall models, which are based on phenomenological approximations of the near-wall Reynolds-averaged equations. Recent work has shown that the structure of the near-wall velocity field and the grid convergence behavior in separated flow regimes are better captured by slip wall models than by traditional equilibrium wall models.

However, modeling the slip length has proven difficult in cases of coarsely resolved high-Reynolds-number flows. To probe this issue, a global optimization procedure is applied to find ideal slip lengths through a posteriori simulations. Results are analyzed for a range of Reynolds numbers, subgrid-scale models, and mesh resolutions in a turbulent channel flow, and a slip length scaling law is identified. Flow over the Boeing speed bump is studied to ascertain the impact of pressure gradients on the slip length scaling. Lastly, these scaling laws are applied to the flow over a realistic airframe (NASA CRM-HL) to test their validity against experimental measurements.