An improved total-shear-stress-conserved wall model for large-eddy simulation with subgrid-scale eddy viscosity fluctuation

The unphysical near-wall turbulent structures observed in wall-modeled large-eddy simulation (WMLES) may lead to the well-known logarithmic-layer mismatch (LLM) and affect the evolution of the flow field. To make the WMLES an effective and practical tool for high-Reynolds number wall-bounded turbulent flows, it is crucial to accurately represent the near-wall turbulent structures. In the present study, by systematically investigating the effect of the subgrid-scale (SGS) eddy viscosity fluctuation (ν¯sgs′) on WMLES, it is revealed that neglecting ν¯sgs′ within the wall model region results in unphysical near-wall turbulent structures as the wall-parallel grid resolution increases. To address this issue, an SGS eddy viscosity modification model based on the instantaneous local momentum equation is proposed, which naturally satisfies the total-shear-stress-conserved constraint while incorporating the effect of ν¯sgs′. The unphysical near-wall turbulent structures are effectively eliminated, with no LLM phenomenon observed in turbulent channel flows at Reτ=550 and 2000. The results also demonstrate the ability of the proposed model to capture very-large-scale motions in the outer layer and their interactions with the inner layer. Furthermore, a preliminary “high-grid resolution” criterion is proposed to determine when ν¯sgs′ should be incorporated in WMLES. Overall, the present study highlights the importance of ν¯sgs′ in WMLES and provides a practical wall model that effectively eliminates unphysical near-wall turbulent structures and avoids the LLM phenomenon.