Effect of chequerboard-type dynamic roughness on turbulent channel flows – a DNS study

The effect of distributed roughness on turbulent boundary layer flows is a topic of fundamental importance for the elucidating of wall turbulence dynamics and for the advancement of flow control strategies aimed at reducing the frictional drag. Dynamic roughness, generated by moving small areas of the wall surface, can be an entirely new realm of drag control, with parameterizations in terms of the frequency of oscillations and other input parameters such as roughness height, spacing, and shape. In this investigation, we are concerned with the response of wall turbulence to distributed chequerboard-type dynamic roughness, oscillating harmonically at a given frequency. Results from several preliminary direct numerical simulations of turbulent channel flows, featuring dynamic roughness on both walls, will be presented and discussed. By targeting a range of frequencies, spanwise/streamwise wavenumbers, and roughness heights, we will quantify the effect that dynamic roughness has on the skin friction, various turbulent statistics, and turbulent flow structures.