Near-wall turbulent fluctuations and coherent structures in wall-modeled large-eddy simulation

Wall-modeled large-eddy simulation (WMLES) of turbulent channel flow is performed to evaluate its predictive capability for near-wall turbulent fluctuations, coherent structures, and turbulence kinetic energy (TKE) budget—aspects that have received relatively little attention in previous studies. Our investigation begins with a low Reynolds number case (Reτ ≈ 1000) to establish the baseline performance of WMLES, followed by an assessment of its generalizability under moderately higher Reynolds number conditions (Reτ ≈ 5200). The results show that WMLES tends to overestimate the low-wavenumber (frequency) component of wall pressure fluctuations. Two convection ridges are observed in its wavenumber-frequency spectra. Further analyses reveal that the additional low-speed convection ridge is primarily attributed to the low-speed wall-attached eddies. When the first-layer grid height is large, these wall-attached eddies are nonphysically elongated in the wall-normal direction. Under-resolving buffer layer degrades streak coherence, suppresses ejection (Q2), and sweep (Q4) events. The probability density function of streamwise velocity fluctuations at y+=15 tends to a Gaussian distribution, indicating a loss of turbulence anisotropy and intermittency. Additionally, a term-by-term comparison of TKE budget equation indicates a shift in the turbulent core region near the wall—from a fully resolved balance between turbulence production (Pk) and viscous dissipation (ε) to a balance dominated by Pk and turbulent transport (Tk). To improve the predictive accuracy of WMLES for near-wall turbulence fluctuations and coherent structures, appropriately resolving the buffer layer (Δyw+=10) is essential. The conclusions of this study are consistent across the range of Reynolds numbers considered.