Effect Of Synthetic Jet Orifice Size On Turbulent Boundary Layer Control

The air-friction drag of high-speed objects and the friction produced by the inner wall of the transportation pipeline mostly comes from skin-friction drag,which will consume a lot of energy.The skin-friction on the wall is closely related to the existence of turbulent boundary layer.Turbulent boundary layer(TBL)control techonology can reduce friction resistance effectively,and bring great engineering and economic benefits.In this paper,the open-loop control system is composed of hot wire measurement technology,d SPACE real-time simulation control system and synthetic jet acuatorr made of piezoelectric ceramic.In this paper,the influence of the slit size of zero mass jet actuator on turbulent boundary layer is studied by using the system,so as to find the optimal control parameters.The expriment use boundary layer hot wire probe to measure the influence of driving frequencies f_s⁺(=f_sv/u_?²ranging from 0.28?0.85,v means kinematic viscosity and u_? means friction velocity of air)and different driving voltage V_p-p(=5 V?90 V,AC of sin function)on drag reduction.The results show that the local wall drag reduction increases first and then decreases with the increase of driving voltage,and the same change law is observed with the increase of driving frequency.This study explores impact of five synthetic jet actuators with different slit sizes(including three synthetic jet actuators with slit width of 1 mm,slit length of18 mm,24 mm and 30 mm respectively,and synthetic actuators with slit length of24 mm and slit width of 0.75 mm and 1.5mm)on turbulent boundary layer,The best skin-friction drag reduction and the best control parameters of each actuator are obtained.The maximum local drag reduction of the five actuators are 47%(optimal control parameters f_s⁺=0.71,V_p-p=35 V),51%(optimal control parameters f_s⁺=0.71,V_p-p=60 V),31%(optimal control parameters f_s⁺=0.57,V_p-p=65 V),33%(optimal control parameters f_s⁺=0.71,V_p-p=25 V),43%(optimal control parameters f_s⁺=0.57,V_p-p=70 V).The best effect of the five actuators is the synthetic jet actuator with the slit length of 24 mm and the slit width of 1 mm.The five actuators are used to control the optimal driving voltage and frequency respectively,and the change of downstream recovery area is measured by hot wire probe.The length of the five actuators downstream recovery area are 310,370,210,230 and 280 wall units respectively.It is found that the length of recovery area is related to the maximum local drag reduction.The larger the local drag reduction,the longer the recovery area.By analyzing velocity signal of the boundary layer hot wire probe and the data of PIV image technology,it has been found that the physical mechanism of skin-friction drag reduction in the near wall area revealed deeply.The intensity of bursting events decreases,and the quasi-stream-vortices(QSVs)are uplifted and then suppress the interaction between QSVs and the wall surface,thus reducing the surface friction.The vortex structures of the synthetic jet actuator with the slit length of 24 mm and slit width of 1 mm is larger and strength is stronger,and the lifting of the QSVs is the most obvious,and the control effect is better.