| The synthetic jet technology is a new method of active flow control. The jet is synthesized at the outlet of the actuator cavity through its volume variations caused by periodic membrane oscillations. Within a cycle of the fluid in and out of the cavity, the net mass flux is zero but the net momentum is non-zero. Controlling the flow in relatively large area can be realized by a small, localized energy input. Thus the technology, regarded as a breakthrough in flow control, has become an important research direction in the areas of active flow control and will be found applications in aerospace engineering.This dissertation aims at the fundamental research on synthetic jet technology. Emphasizes have been placed on the mechanism of the formation and evolution of synthetic jet via numerical simulations and experiments. To enhance the driving ability of the actuator, a new half cymbal piezoelectric-metal composite membrane is explored. Besides, to effectively process the non-stationary signal of the synthetic jet recorded during the experiment, a new signal processing method is employed. The detailed research is including:Firstly, a two dimensional incompressible RANS model is established. Several existing viscous models are studied for the suitability to describe the synthetic jet phenomena. Numerical simulations are conducted by utilizing these viscous models, and the simulated results are compared with experiment data to determine the best suitable model. Secondly, the formation mechanism and the evolution process of the synthetic jet are simulated numerically with the chosen model. The behavior of the time and spatial distributions of the jet velocity are investigated. Relationships of the output velocity with the cavity geometry, the outlet shape, as well as the tilt angle between the outlet centerline and the wall are studied to provide a reference for the optimization design of the actuator cavity structure. Thirdly, a new kind of half cymbal piezoelectric-metal composite membrane (HCPCM) is proposed in order to improve the driving ability of the membrane. A finite element model of the HCPCM has been established and its dynamic behaviors are analyzed by using the commercial FE software ANSYS. The membrane structure is optimized based on the finite element simulations. Besides, another new kind of actuator with dual HCPCM is also proposed. Experiments have been performed. Experimental results reveal that the displacement of the HCPCM is approximately 2.6 times larger than that of conventional plane membrane. Fourthly, based on the gathered information, several synthetic jet actuators with HCPCM and traditional plane membranes are manufactured and tested. The jet flow field is measured by using the pitot anemometer, Hot Wire Anemometer (HWA) and Particle Image Displacement Velocimetry (PIV). The optimized geometry of the actuator is also determined by the experiments. Measured data verify the correctness of the simulations. Results also reveal that the HCPCM does raise the synthetic jet velocity at the outlet and thus enhance the driving ability of the actuator. Finally, Hilbert-Huang Transform (HHT) is introduced into the signal analysis of fluid field. Signals of the instantaneous jet velocity are collected by using the HWA and are then processed with HHT. The processed results provide clear physical meanings of the jet. It may conclude that HHT is an effective method for the processing of signals in the flow field.The research is financially supported by the National Science Foundation of China (No: 90405008).
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