Direct numerical simulations of turbulent channel flows with sinusoidal walls

Highly-resolved, direct numerical simulations of turbulent channel flows with sub-Kolmogorov grid resolution are performed to investigate the characteristics of wall-bounded turbulent flows in the presence of sinusoidal wall waviness. The wall waviness serves as a simplified model to study the effects of well-defined geometric parameters of roughness on the characteristics of wall-bounded turbulent flows. In this study, a two-dimensional wave profile with steepness ranging from 0.06 to 0.25 and wave amplitudes ranging from 9 to 36 wall units were considered. For the smooth and wavy-wall simulations, the Reynolds number based on the friction velocity was kept constant. To study the effects of wave amplitude and wavelength on turbulence, two-dimensional time and spanwise averaged distributions of the mean flow, turbulent kinetic energy, and Reynolds stresses as well as turbulent kinetic energy production and dissipation are examined. Furthermore, in order to provide a more direct comparison with the smooth-wall turbulent channel flow one-dimensional profiles of these quantities are computed by averaging them over one wavelength of the wave profile. A strong effect of the wall-waviness and, in particular, the wave amplitude and wavelength on the characteristics of the turbulence was obtained. Wall waviness mainly affected the inner flow region while all recorded turbulent statistics collapsed in the outer flow region. Significant reductions in turbulent kinetic energy, production and dissipation were obtained with increasing wave amplitudes when reported in inner scale. While production is lower for all wavy wall cases considered here in comparison to the smooth wall, reducing the wavelength caused an increase in production and a decrease in dissipation.