Used In The Thrust Direction Control Of The Micro-jet Technology

Thrust Vector control is one of objects being seeked by engineers in rocket propulsion area. There came a new flow control technique called microjet in the 1990s, which was based on the theories of nonlinear complex system and chaos. The core of the technique is the microjet produced by a micro-actuator driven through electrical signal. The most attractive advantage of the microjet technique is that its working substance comes from environment and related tank, piping and valve can be omitted. Research results in aboard show that the microjet technique has vast prospects for application. In addition to active flow control, it can also be used as boundary layer control, aerodynamic resistance reduction, combustion strengthening and cooling improvement. Therefore, rudimentary theoretical analyses and experimental investigations of microjet were accomplished in this thesis to provide some basic information and methods for following research and future engineering applications of the technique.Since the tight relationship between the microjet technique and MEMS, a general introduction to MEMS was performed in the thesis. What抯 more, some basic knowledge on vortex was also introduced because its important role in the flow field of microjet.By solving the 2-D viscous Navier-Stocks Equation, the flow field of the microjet was simulated. The results clearly reveal the features of microjet and the process of vortex pairs?formation, advection, diffusion and entrainment effection on ambient fluid. By comparing the flow fields of microjet under different working parameters, the law of jet strength changing with driving frequency was obtained. The result shows that a new kind of flow will be produced instead of the microjet when frequencies exceed a critical value, suppose the characteristic velocity of the micro-actuator remains constant. Its peculiarity is that the vortex pair formed on the ejection stroke can抰 move far enough under the self-induced velocity, so the vortex pair is sucked into the cavity of the actuator during the suction stroke.Under the preliminary experimental research, the micro-actuator was substituted by a buzzer, water and ink were separately used as working substance and coloring agent. By submerging the buzzer into the water, the working condition of the microjetwas satisfied. It validates the results obtained from numerical simulation. In the near field, the vortex pairs are gradually and periodically formed, and at the same time they migrate down stream under the self-induced velocity. In addition, the vortex pairs are discrete. Make a comparison among different driving signals, including square, triangle, sinusoidal and sawtooth wave, it is shown that the square wave has the best driving result and the sawtooth wave has the worst one. Through measuring the jet length, the following law is obtained: there exists an optimal driving signal frequency that can produce the strongest microjet for a certain actuator configuration at constant input power.