Direct Numerical Simulations of rough wall-bounded turbulence over unsteady channel flow

Direct Numerical Simulations of unsteady channel flow has been performed over a regular rough surface in order to investigate the physics involved near the wall vicinity and unsteady effect of pulse applied periodically. Unsteady flow has been initiated by applying an unsteady nonzero mean forcing in the form of a time-varying pressure gradient. Forcing frequencies categorized into low to high amplitude of oscillations ranging from 5% to 10% of mean centerline velocity. The simulation of two different Re_τ of 180 and 395 was performed and compared with the near-wall turbulence statistics. Our aim is to investigate the difference in turbulence statistics of the smooth side with the rough side such as mean statistics, phase averaging of the unsteady channel wall. Further extending the findings of the streaks response for both the Reynolds number on the rough turbulent surface vicinity. The current simulation indicates the difference in a structure near the wall as the Reynolds number increase. Due to roughness, small and strong vorticity was observed between the viscous sublayer and buffer layer for the Re_τ of 395 compared to Re_τ of 180. The viscous sublayer for the higher Re_τ shows a higher turbulent structure over the rough wall but that structure has minimal to no contribution over the buffer layer.