Breakdown of Low-Speed Streaks under High-Intensity Background Turbulence

Abstract

Breakdown of low-speed streaks under high-intensity background turbulence is studied experimentally through artificially generating spanwise-periodic low-speed streaks in a boundary layer downstream of two-dimensional local suction. The suction is applied to a developed turbulent boundary layer such that nearwall turbulence structures are completely sucked out but most of turbulent vortices in the original outer layer survive the suction. Spanwise-periodic low-speed streaks are generated in such a quasi-laminar boundary layer by using a periodic array of small screens. The results show that the suction-survived turbulence soon excites sinuous motion of low-speed streaks leading to the streak breakdown. Under the present energetic background turbulence, the streak breakdown is found to be not caused by the linear instability but by the transient disturbance growth.