2011/06/23 by YUKINORI KAMETANI, Yukinori Kametani, KOJI FUKAGATA +1 · 2 citations
Engineering · Environmental Science · #Fluid Dynamics and Turbulent Flows #Heat Transfer Mechanisms #Wind and Air Flow Studies
paper · doi:10.1017/jfm.2011.219
Direct numerical simulation (DNS) of spatially developing turbulent boundary layer with uniform blowing (UB) or uniform suction (US) is performed aiming at skin friction drag reduction. The Reynolds number based on the free stream velocity and the 99% boundary layer thickness at the inlet is set to be 3000. A constant wall-normal velocity is applied on the wall in the range, −0.01 U ∞ ≤ V ctr ≤ 0.01 U ∞ . The DNS results show that UB reduces the skin friction drag, while US increases it. The turbulent fluctuations exhibit the opposite trend: UB enhances the turbulence, while US suppresses it. Dynamical decomposition of the local skin friction coefficient c f using the identity equation (FIK identity) (Fukagata, Iwamoto & Kasagi, Phys. Fluids , vol. 14, 2002, pp. L73–L76) reveals that the mean convection term in UB case works as a strong drag reduction factor, while that in US case works as a strong drag augmentation factor: in both cases, the contribution of mean convection on the friction drag overwhelms the turbulent contribution. It is also found that the control efficiency of UB is much higher than that of the advanced active control methods proposed for channel flows.