Time-averaging and temporal-filtering in wall-modeled large eddy simulation

Abstract

A turbulent channel flow at a Reynolds number of Reτ=2000 is solved based on the spatially filtered Navier–Stokes equations using large eddy simulation and an in-house code. A nonequilibrium wall model is implemented to predict the flow in the wall layer based on the Reynolds-averaged approach. To mitigate the log-layer mismatch, which is often encountered in wall modeling, two temporal schemes are introduced to average the wall layer solution and to filter the flow information input to the wall layer. It is found that the time periods used for the time-averaging and temporal-filtering schemes affect the performance of the wall model. The results show that shorter time periods enable the wall model to respond to the flow structures in the outer layer and correctly predict the friction velocity. However, the prediction of the friction velocity also depends on the location of the matching point. Locating the matching point further from the wall results in better performance due to the compatibility of the subgrid scale model with the grid resolution further from the wall. The temporal-filtering scheme is used to remove nonessential high-frequency wavelengths that can disturb the functionality of wall modeling. Various combinations of the time-averaging and temporal-filtering time periods are investigated for different locations of the matching point. Overall, it is concluded that using a shorter period for time-averaging and a temporal-filtering period comparable to the turbulent diffusion timescale leads to improved results.