Skin Friction Drag Reduction Based on Plasma-Induced Streamwise Vortices

This work aims to manipulate a fully developed turbulent boundary layer over a flat plate based on plasma-induced streamwise vortices, with a view to reducing the friction drag. Four different plasma actuator configurations for generating streamwise vortices were explored. A surface balance technique is deployed to measure the skin-friction drag. A new calibration method is proposed for this technique to resolve accurately the friction drag change. It is found that the plasma-actuator-generated vortices and their interactions with the boundary layer may lead to a substantial drag reduction. The control efficiency is also estimated. A single hotwire is used to measure the streamwise velocity fluctuation u in the turbulent boundary layer, while flow visualization is performed in the buffer layer, which reveals that the low-speed streaks are pushed by the plasma force toward the centre of the actuator pair, forming a barrier that interferes the turbulence production cycle, and hence allowing substantial drag reduction.