Synthetic near-wall small-scale turbulence and its application in wall-modeled large-eddy simulation

Abstract

A suitable representation of the universal near-wall small-scale motions helps the understanding of physical mechanisms as well as the development of simulation techniques of wall turbulence. Minimum flow unit (MFU) as a reduced-order model of wall turbulence serves the purpose, but requires non-trivial computational cost. Motivated by improving the MFU-based near-wall turbulence prediction model [Yin et al., “Prediction of near-wall turbulence using minimal flow unit,” J. Fluid Mech. 841, 654–673 (2018)] for better use in large-eddy simulations (LES), the present study seeks to supply near-wall small-scale turbulence fluctuations with synthetic flow fields generated from universal model of MFU, thus avoiding the auxiliary simulation and lowering the computational cost. We first obtain MFU data ranging from Reτ=2000 to 8000 using direct numerical simulations and reconstruct 3-dimensional space–time spectra of MFU using the generalized local modulated wave method. The space–time spectra serve as the universal model of near-wall small-scale turbulence. We then propose a method to generate turbulent flow fields from space–time spectra, based on the synthetic random Fourier method. The generated flow is statistically consistent with and structurally similar to the authentic MFU. At last, the generated flow fields at different Reynolds numbers are applied to LES of off-wall channels, and the reasonable results obtained suggest that our synthetic near-wall small-scale turbulence is as effective as authentic MFU in constructing off-wall boundary conditions.