Low Speed Streaks Instability of Turbulent Boundary Layer Flows with Adverse Pressure Gradient

摘要

A Direct Numerical Simulation of turbulent flow subjected to an adverse pressure gradient (APG) was performed. As already noticed by many authors in such configurations, a second outer peak of turbulent kinetic energy is observed in the region of APG. In the present configuration, this peak is due to the production of intense vortices which are shown to be related to the instability of low speed streaks. The turbulent boundary layer flow subjected to an adverse pressure gradient (APG) induced by curvature is of crucial importance for many applications including aerodynamics of airfoils, ground vehicles or turbine blades. Significant progress is needed in understanding the near wall turbulence in order to improve the theoretical and numerical models. The available numerical models usually fail to predict flows at the onset of separation as they are based on scalings which are no more valid with pressure gradient. In flows with adverse pressure gradients, a strong secondary peak of turbulent kinetic energy has been observed in many configurations and is not yet fully explained [7]. Therefore, a careful analysis of turbulent structure generation is an opportunity to make progress in designing accurate statistical models for turbulence. Using the numerical solution procedure documented in [4] a database of channel flow with curved wall has been generated at Reynolds number Reτ ≈600. The flow slightly separates at the lower curved wall and is at the onset of separation at the upper wall. Therefore, two different configurations of pressure gradient as well as the effect of wall curvature can be investigated and compared.