Aiming at the problem of continuous control of asymmetric forebody vortices at a high angle of attack in a bi-stable regime, a dual synthetic jet actuator embedded in an ogive forebody was designed. Alternating unsteady disturbance with varying degree asymmetrical flow fields near the nozzles is generated by adjusting the duty cycle of the drive signal of the actuator, specifically embodying the asymmetric time-averaged pattern of jet velocity, vorticity, and turbulent kinetic energy. Experimental results show that within the range of relatively high angles of attack, including the angle-of-attack region in a bi-stable state, the lateral force of the ogive forebody is continuously controlled by adjusting the duty cycle of the drive signal; the position of the forebody vortices in space, the vorticity magnitude, the total pressure coefficient near the vortex core, and the vortex breakdown location are continuously changed with the duty cycle increased observed from the time-averaged flow field. Instantaneous flow field results indicate that although the forebody vortices are in an unsteady oscillation state, a continuous change in the forebody vortices’ oscillation balance position as the duty cycle increases leads to a continuous change in the model’s surface pressure distribution and time-averaged lateral force. Different from the traditional control principle, in this study, other different degree asymmetrical states of the forebody vortices except the bi-stable state are obtained using the dual synthetic jet control technology.
In view of the control effects of fluidic thrust vector technology for low-speed aircraft at high altitude/low density and low altitude/high density are studied. The S-A model of FLUENT software is used to simulate the flow field inside and outside the nozzle with variable control surface parameters, and the relationship between the area of control surface and the deflection effect of main flow at different altitudes is obtained. It is found that the fluidic thrust vectoring nozzle can effectively control the internal flow in the ground state and the high altitude/low density state. and the mainstream deflection angle can be continuously adjusted. The maximum deflection angle of the flow in the ground state is 21.86°, and the maximum deviation angle of the 20 km high altitude/low density state is 18.80°. The deflecting of the inner flow of the nozzle is beneficial to provide more lateral force and lateral torque for the aircraft. The high altitude/low density state is taken as an example. When the internal flow deflects 18.80°, the lateral force is 0.32 times the main thrust. For aircraft with high altitude and low density, sufficient lateral and lateral torque can make the flying aircraft more flexible, which can make up the shortcomings of the conventional rudder failure and even replace the conventional rudder surface.
The lateral hysteretic characteristic generated by asymmetric vortical flow behind the tangent-ogive cylinder is investigated without and with micro synthetic jet control, when the slender body undergoes a large amplitude pitching motion. Experiments are conducted in a low speed wind tunnel of Nanjing University of Aeronautics and Astronautics at a Reynolds number of 46000. The change rule of the instantaneous pressure distribution reflects the aerodynamic characteristic of the whole model. The data of temporal flow file are acquired using particle image velocimetry locked-phase method and present the asymmetric vortices evolution. Results show that asymmetric vortices still exist in the leeward of the slender body during the dynamic pitching motion. However, the asymmetric degree of the vortices distribution, swirling strength and breakdown location are different which is greater in the downward pitching than in the upward pitching, which leads to the lateral force hysteretic phenomenon. In addition, the hysteretic loop expands as the reduced frequency increased. It is an effective method of the flow control that uses micro synthetic jet alternative blow to control the lateral force in the dynamic pitching motion. Furthermore, the lateral force, the pressure distribution and the hysteretic loop shape are changed continuously as the duty cycle of the control signal increased. For the duty cycle of 50%, the vortices distribution, the swirling strength and breakdown location tend to be symmetrical, so the lateral force decreases significantly and the hysteretic loop is eliminated.
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