Friction drag reduction of a spatially developing boundary layer using a combined uniform suction and blowing

摘要

Uniform suction or blowing from the wall is one of the methods to reduce the friction drag. The uniform suction improves the stability of a laminar boundary layer: the transition will be delayed and the overall friction drag will be reduced due to the extended laminar region. In contrast, the uniform blowing is known to reduce the drag in the fully-turbulent regime. Therefore, a combination of uniform suction and blowing is expected to be effective for flows involving transition, such as the flow around an airfoil, by delaying the transition near the trailing edge and by reducing the turbulent drag in the post-transition (i.e., turbulent) region. The objective of this study is to investigate the friction drag reduction effect of such a combined uniform suction and blowing. The Reynolds-Averaged Navier-Stokes simulation is used to deal with a spatially developing boundary layer on a flat plate at a practically high Reynolds number. As a result, the combined control is found to reduce the global skin friction coefficient by 44.1%, whereof the contribution of transition delay by the uniform suction is about 90%, and that of turbulent drag reduction by the uniform blowing is about 10%. It is also found that the position of the blowing region should better be located in the upstream side of the turbulent region because the drag reduction effect is sustained for a while even after the blowing is terminated.