A Sensor-Based Laminar-Turbulent Wall-Stress Model for Large Eddy Simulation

Abstract

Wall-modeled large eddy simulations (WMLES) are becoming an increasingly viable tool to study complex unsteady turbulent flows. Conventional wall models applied in these simulations are however not applicable to laminar boundary layers. While these encompass only a tiny fraction of the total surface area, erroneous predictions in this region of the flow can greatly impact the downstream flow field. In the present study, a new wall model is proposed by combining the laminar wall model and turbulent wall model with the use of a transition model marking the laminar and turbulent regions. The proposed wall model is applied to the laminar flat plate, wedge and laminar NACA 0012 flow. Results show that errors incurred at the unresolved leading edge, where the similarity solution used by the laminar wall model is invalid, accumulate in the velocity profiles for the flat plate and wedge flow cases. In underresolved regions near the leading of the NACA 0012 or near the tip of the wedge, good approximations to reference data have been found. The proposed wall model is also applied to a high Reynolds number flow involving an airfoil near stall. The proposed wall model shows promising results with good agreement for the skin friction distribution, especially in capturing the laminar skin friction peak if the transition location is known. However, the transition sensor considered for switching between the laminar and turbulent mode of the wall-stress model performs unsatisfactory. Other discrepancies in the results, such as capturing the laminar separation bubble and trailing edge separation are attributed to the relatively coarse meshes used. Last but not least, the computational cost incurred by the new wall model is marginal.