Parametric Study Of Plasma Actuators For Turbulent Boundary Layer Control

The turbulent boundary layer control has been received a great attention in literature.The drag in turbulent boundary layer is mainly caused by the coherence structure near wall.This work is to control the turbulent boundary layer using DBD plasma actuator,with a view to reducing drag.The dielectric barrier discharge(DBD)plasma actuator is a device which generates ionic wind along the wall.Depending on the orientation of the actuator with the respect to the mean flow,streamwise vortex is formed and could be useful to manipulate the turbulent boundary layer.The streamwise vortex should be optimized for the maximum drag reduction in turbulent boundary.The size,vortex core and maximum vorticity of the vortex are very important parameters to manipulate the turbulent boundary layer.Three parameters,i.e.the length of the actuator,yaw angle of actuator and applied voltage on the actuator,have been investigated in the experiment.The PIV system is the main technique to measure the flow filed with and without control.Hotwire is deployed to measure velocity profile or velocity in the linear region to estimate the skin friction.A calibration technique has been developed for the force balance in order to measure skin friction drag over an area behind the actuators.The decrease of the maximum vorticity induced by DBD plasma actuator could be achieved by increasing the length of the actuator or reducing the applied voltage while other parameters remain unchanged.On the other hand,in order to keep the vorticity of the vortex at a constant,the longer electrode of the actuator should be used with the higher voltage.When the length of the actuator and the applied voltage are remained unchanged,the yaw angle of the actuator may increase the spanwise distribution of drag,though the maximum vorticity decreases with the larger yaw angle.It is believed that the drag will be reduced when the vortex is large enough to control the turbulent boundary layer and small enough not to add additional drag.When fix the length of the actuator to 10 cm and the voltage to 9 kVp-p,the integration of spanwise drag change may result a maximum of 7.9% drag reduction.Note that the maximum local drag reduction is about 19% with 15 degrees yaw angle.It is suggests that for a weaker vortex or large size of vortex could eventually lead to drag reduction.