A time-average filtering technique to improve the efficiency of two-layer wall models for large eddy simulation in complex geometries

摘要

Two-Layer wall models have been recurrently studied since they represent a good physical model for Large Eddy Simulations with underresolved wall regions. Specifically, those based on the Reynolds Averaged Navier-Stokes equations are of special interest, since they can be applied to a wide range of conditions including non-equilibrium flows. Nonetheless, these models are affected by two recurrent problems, the "log-layer mismatch" and the resolved Reynolds stresses inflow, which until now, have been dealt with separated techniques. In this work, a time-filtering methodology is applied to tackle both issues at once with a single and low-computational-cost step, easily applicable to complex three-dimensional geometries. The time-filtering technique has already been applied to other types of wall models to mitigate the "log-layer mismatch." Now, it is applied for the first time in the Two-Layer wall model context, showing its ability not only in avoiding the mismatch issue but also in blocking the resolved Reynolds stress inflow, dramatically improving the wall model performance and generality compared to other existing implementations. A methodology to determine the necessary temporal filter length is proposed and validated in equilibrium and non-equilibrium conditions. Additionally, the filter size influence on large-scale unsteady flow motions is assessed. Good results are obtained in steady and unsteady flow regimes by suppressing the LES highest frequencies while taking into account large-scale temporal effects. (C) 2019 Elsevier Ltd. All rights reserved.