On the persistence of large-scale turbulent structures in turbulent Couette flow with wall-transpiration

It has long been known that turbulent Couette flows (TCF) are dominated by large-scale turbulent structures of vortex-type in stream-wise direction (for an early experimental and numerical validation see e.g. Tillmark et al. 1995 and Bech et al. 1995), and a recent DNS study supports the persistence up to $Re_{\tau}=550$ (Avsarkisov et al. 2014). In an ongoing DNS study the TCF is extended towards wall transpiration, i.e. blowing from below and suction at the top at constant velocity $v_0$. Even at small transpiration rates, i.e. $v_o/u_w\ll 1$, where $u_w$ is the moving wall velocity, strong changes in the overall flow behavior is visible. E.g. a strong reduction of the mass-flux is observed. Beside interesting and new scaling issues, one of the most remarkable feature of this largely unexplored flow is, that even at the highest transpiration rates investigated so far, the footprints of the large turbulent rolls of the TCF are still visible at the highest Reynolds and transpiration number. Other quantities such as two-point auto-correlations, two-dimensional spectral energy densities and pre-multiplied spectra give a more detailed picture of the turbulent structure and support the finding of highly persisting large-scale turbulent structures in TCF with wall-transpiration.