Statistics and structure of spanwise rotating turbulent channel flow at moderate Reynolds numbers

摘要

A study of fully developed plane turbulent channel flow subject to spanwisesystem rotation through direct numerical simulations is presented. In order tostudy both the influence of the Reynolds number and spanwise rotation onchannel flow, the Reynolds number $Re = U_b h/\nu$ is varied from a low 3000 toa moderate $31\,600$ and the rotation number $Ro = 2 \Omega h/U_b$ is variedfrom 0 to 2.7, where $U_b$ is the mean bulk velocity, $h$ the channel half gapand $\Omega$ the system rotation rate. The mean streamwise velocity profiledisplays also at higher $Re$ the characteristic linear part with a slope nearto $2 \Omega$ and a corresponding linear part in the profiles of the productionand dissipation rate of turbulent kinetic energy appears. With increasing $Ro$a distinct unstable side with large spanwise and wall-normal Reynolds stressesand a stable side with much weaker turbulence develops in the channel. The flowstarts to relaminarize on the stable side of the channel and persistingturbulent-laminar patterns appear at higher $Re$. If $Ro$ is further increasedthe flow on the stable side becomes laminar-like while at yet higher $Ro$ thewhole flow relaminarizes, although the calm periods might be disrupted byrepeating bursts of turbulence, as explained by Brethouwer (2016). Theinfluence of the Reynolds number is considerable, in particular on the stableside of the channel where velocity fluctuations are stronger and the flowrelaminarizes less quickly at higher $Re$. Visualizations and statistics showthat at $Ro=0.15$ and 0.45 large-scale structures and large counter rotatingstreamwise roll cells develop on the unstable side. These become lessnoticeable and eventually vanish when $Ro$ raises, especially at higher $Re$.At high $Ro$, the largest energetic structures are larger at lower $Re$.