Drag Reduction In Turbulent Boundary Layer Based On Plasma Actuators With AC-DC Actuation Signal

Advances in technology in the 21st century have driven cars,ships and aircraft vehicles faster and faster,and the speed of vehicles has been accompanied by increased wall frictional resistance,most of this is due to the turbulence created by the surface of the vehicle.The frictional resistance of the wall surface exists in the turbulent boundary layer.In order to save energy and improve energy efficiency,it is particularly important to control the frictional resistance in the boundary layer.In this paper,two new actuation signals are proposed for the actively control plasma actuators,and the drag reduction of large streamwise vortex generated by the plasma actuators driven by new signal is studied.This experimental proposed the AC-DC and AC-pulse DC two new drive signals.The driving signals program were programmed by Labview software.The vortex structure and velocity field of the plasma actuators are calibrated under the AC-DC driving signal and applied to the turbulence boundary layer.The constant temperature hot wire anemometer is used to study the change of drag reduction under different drive signal control parameters,and according to hot wire data to determine the optimal drag reduction control parameters,and then take the PIV on the y-z plane at the downstream x+=166.7 and statistical analysis of the hot wire signal to study the change of the flow structure.Then apply the AC-DC drive signal to the feed-forward PD control program,find the optimal control coefficients.The results show that under the excitation of AC-DC driving signal,the maximum jet velocity generated by the plasma actuator appears at a position 1 mm away from the wall surface,and the trajectory of the vortex generated by the plasma actuator is not influenced by the duty cycle parameter in one cycle.The local drag reduction under different control parameters is measured when the actuation voltage Vp-p=4.5-6.5 kV,frequency f=10-100 Hz and duty cycle Dt=10-100%,the results show that the local drag reduction is not affected by the frequency.At x+=166.7,the optimal drag reduction control parameter is Vp-p=6.5 kV,f=100 Hz,Dt=90%.Under this control parameters,the local drag reduction can up to 21%and 37%at z+=0 and z+=100 respectively,the reason for this phenomenon is that the vortex generated by the plasma actuators is closer to the wall surface after mixing with the incoming flow,and the vortex structure sways in the y-z plane,destroying the near wall structure of the turbulent boundary layer.And in-233 ≤z+≤233 region the average drag reduction is 15%,and the flow recovery area is 1400 wall units at z+=100.When the excitation voltage is 6 kV,the power consumption of this signal is reduced by 19%than the sine wave which frequency is 2000 Hz,and the drag reduction efficiency is increased by 150%.Under the AC-DC signal exciatation,the downstream burst frequency is increased but the burst strength is reduced,the linear region in the turbulent boundary layer is thickened and the buffer layer is compressed;in the feed-forward PD control program,by adjusting different proportional coefficients Kp and differential coefficient Kd and measuring the local drag reduction,when the coefficient Kp=26 and Kd=0.5,the local drag reduction is up to 32%.