Direct numerical simulation of turbulent channel flow with passive scalar: analysis of spectra and interscale transfers for use in large eddy simulation framework

We perform highly resolved direct numerical simulations (DNS) of a fully-developed turbulent channel flow subjected to constant heat or passive scalar fluxes qw both walls. The Reynolds number Rτ=uτδ/ν is of order 400, and the Prandtl numbers considered are Pr=0.1, 1 and 10. We propose several methods to identify the transfer processes governing turbulent energy and passive scalar variance using transport equations developed in both spectral and physical spaces, highlighting the link unifying them. Besides Fourier analysis performed in spectral space along the two homogeneous directions, we extend scale analysis to non-homogeneous turbulence via a filtering process in physical space. As numerical results, we compute Kolmogorov and Batchelor length scales, turbulence and scalar field intensities, transport equation budgets for kinetic energy and scalar variance, spectra and energy transfer at various channel locations. The results suggest the spectra exhibit a degree of universality, even in non-homogeneous flow. The energy transfer evolutions are consistent with physical expectations, demonstrating energy transfer from low to high wavenumber regions.