Experimental investigation on the transient process of jet deflection controlled by passive secondary flow

The passive fluidic thrust vectoring technology is highly applicable in the next-generation high-maneuverability and high-stealth aircraft. Jet deflection control plays an important role in passive fluidic thrust vectoring control. In this research, we developed a passive fluidic thrust vectoring nozzle, which can control the primary jet to deflect between the attached state and detached state by controlling the passive secondary flow. Based on this model, the transient process of unsteady near-wall flow structures evolution during jet deflection as well as the mechanism of jet deflection control are investigated. Particle image velocimetry measurement is applied to obtain time-averaged flow topological structures of the jet in two steady states. High frame rate smoke visualization is applied to investigate the transient characteristics of the near-wall unsteady flow structures such as shear layer vortices, secondary flow, and trailing edge backflow. The results show that in the near-wall region, the entrainment of the shear layer fights against the replenishment of the secondary flow and the backflow. Thus, the mass flux of the near-wall region is in dynamic balance, which means the total amount of fluid in this region is invariant. Shutting off or opening the secondary flow is the trigger for the collapse or reestablishment of this mass flux balance. The vanishing or reappearance of the backflow is the dominant cause of jet deflection.