New properties of streamwise streaks in transitional boundary layers

Based on detailed results of direct numerical simulation with high order accuracy and resolution at the late-stages of the transitional boundary layer, new properties are found, such as discontinuous event in the evolution of low-speed streamwise streaks and the appearance called high speed spots in the development of high-speed streamwise streaks. In the present paper, the complex vortex structures and the ejection-sweep phenomenon in the transition process of boundary layers are analyzed thoroughly, and the new properties of high-speed /low-speed streamwise streaks are confirmed to be closely relatcd to the evolution process of vortex structures in the flow-field.