Principle Of Synthetic Jet And Dual Synthetic Jets, And Their Applications In Jet Vectoring And Micro-Pump

Flow control is one of leading area of research in aviation and fluid dynamics, and in 21st century, the most important breakthrough in aerodynamics may be made at the area of flow control. Synthetic jet (SJ) is a zero mass flux jet in nature, and the unique characteristics of the synthetic jet flow-field and the working attributes of the actuators make synthetic jet actuators suitable for a large class of applications, including jet vectoring, control of separation, enhanced mixing, reduction of wall friction, virtual shaping, micro-pump, and so on. Flow control approaches that use synthetic jets have become an important tool for the aerodynamicist,and synthetic jet has been a remarkable and promising active flow control technology for recent decade. However, the synthetic jet actuator hasn't been investigated all-around up to now. In addition, a novel high performance synthetic jet actuator having more advantages and functions, is a key of extending the applications of synthetic jet to more flow control systems and making flow control more effective.In this dissertation, a synthetic jet actuator (SJA) and its applications in jet vectoring and micro-pump are investigated all-around, and then a novel dual synthetic jets actuator (DSJA) is presented and its applications are initially studied. The outlines and conclusions are as follows:The SJA with different exits and the piezoelectric (PZT) vibrator in clamped and simply supported edge conditions are modeled using lumped elements. The equivalent circuit for the SJA and the frequency-resoponse function of the circuit is established to analyze the behavior of the SJA and the delay phase of the synthetic jet. The vibrating characteristics of the PZT vibrator are investigated and an important parameter, a delay phase of PZT vibrator, is put forward for PZT SJAs. According to the vibrating characters of the PZT vibrator, a computing model of the SJA is established, which considers the actuator cavity, the exit throat, and the external flow field as a single computational region. The Hot-wire Anemometry experiments show the synthetic jet velocity with PZT-vibrator in clamped edge conditions almost decreases to one seventh of that in simply supported edge conditions. The startup response of the PZT-SJA is very quickly and within one actuator cycle, and the synthetic jet reaches its final value within several actuator cycles. The SJA is investigated using particle image velocimetry (PIV). A transfer-phase and sub-frequency (TPSF) technique is provided to capture the arbitrary phase of the synthetic jet. And a transfer-phase to equal (TPTE) technique is provided to determine the phase of the synthetic jet. The results indicate a circle of the synthetic jet is divided into four stages. And the delay phase of the synthetic jet is almost equal to that of the PZT-vibrator. Additional to the experimental work, the synthetic jet flow-field is simulated, and numerical results are compared with experiments. Results show the computing model of the SJA and computing methods are correct.The interactions of adjacent SJAs are investigated using PIV. Varying the relative phase or relative amplitude of driving voltage of the adjacent actuators vectors the direction of the ensuing merged jet of the adjacent synthetic jets. And an interaction mechanism of the adjacent vortex pairs, attract-impact causing deflection (AICD), is provided to explain why the merged jet is generally vectored to the side of the phase-leading synthetic jet and the synthetic jet with higher driving voltage.A new actuator called dual synthetic jets actuator (DSJA) is put forward originally; it consists of two sealed cavities bounded on one end by a single diaphragm, two exit slots, and a slide block (SB). In the DSJA concept, two adjacent jets out of phase are established under the two exit slots and are driven by the motion of the same diaphragm, instead of a single jet every vibrating circle from an existing SJA. In the near field downstream, the two jets entrain fluid around them and interact with each other, the flow field is complex and the time-periodic diaphragm dominates them. And there is a phenomenon of"self-support"between the dual synthetic jets; a criterion of"self-support"and a baffle plate are put forward to control the"self-support"between the dual synthetic jets. In the far field downstream, the two jets merge a single, more stable synthetic jet with a higher velocity and a double frequency. The novelties of the DSJA are that the two cavities share the same wall equipped with a single diaphragm and the slide block regulates the two synthetic jets. The novelty that the two cavities sharing the same diaphragm makes the DSJA not only has the unique property of zero-mass-flux anytime in nature, but also resolves the problems of pressure loading and energy inefficiency of the existing synthetic jet actuators. The novelty that the slide block regulates the two jets make the DSJA has a unique thrust-vectoring characteristic that the existing SJAs haven't. And different flow fields of the dual synthetic jets can be generated with slight modifications of the slide block. These novelties bring the major advantages and functions of this DSJA that the existing SJAs do not have. These indicate that the DSJA may potentially replace the existing SJA in various applications and also extend the applications of the synthetic jets to more flow control systems that cannot be implemented by the existing SJAs.Vectoring control of a primary jet with synthetic jets is investigated. A strategy of"bridge"is presented to study the jet vectoring using SJAs. An actuator with novel slope-step exit is presented for jet vectoring. A primary jet vectoring using actuators with different exit modes are simulated. For a given primary jet speed and synthetic jet strength, the vectoring angle of primary jet is the largest one when it controlled by the actuator with slope-step exit. The physical evolution and control mechanism of jet vectoring using SJAs are analyzed and concluded. The physical evolution of jet vectoring is divided into three stages corresponding to three different regions, and the final vectoring angle of the primary jet is a total result of the primary jet controlled by synthetic jet at the three different regions. The lower static pressure near the primary jet exit induced by the synthetic jet, the absorption of primary jet fluid by the SJA during the suction stroke and the entrainment of primary jet fluid by the synthetic jet momentum impulse during the blowing (the momentum impuls may be a resistance), the coupling and interaction between the vortices of synthetic jet and the shear layer of primary jet are the main control mechanisms of a primary jet vectoring with synthetic jet. The main physical factors influencing jet vectoring are analyzed and summarized. The physical factors of the pressure difference, the location and area of the lower pressure region, the component of the synthetic jet momentum and the entrainment ratio of the synthetic jet flow to primary jet flow directly control the vectoring force and the vectoring angle. The source variables of the physical factors are established. A preparatory control model of jet vectoring using SJA is presented, which is composed of a controlling ability function and a regulating function. The preparatory model has the benefit of explaining the efficiency of jet vectoring using SJA with source variables at different values, and it indicates the optimal actuator is taking full advantage of the regulating function. The preparatory control model provides a base for practical applications.Jet vectoring control using the DSJA is investigated initially. The results imply a single dual synthetic jets actuator can play both"push"and"pull"functions of vectoring the primary jet that the existing SJAs cannot. So, it provides an innovative mode for jet vectoring.Based on the unique divisional and controllable characteristics of the synthetic jet flow-field, a valve-less synthetic-jet-based micro-pump is presented; it comprises a synthetic jet actuator, a dividing-clapboard and a mesh filter. The synthetic-jet-based micro-pump has a function of adjusting pump flux and can also resolve the two main problems of fluid leakage and dust clogging on a micro-pump nozzle. The design criterions and control rule of the micro-pump are obtained by analyzing the characteristics of synthetic jet flow-field. The computing results show the work efficiency of the micro-pump on design condition is high and the designing criterions of the dividing-clapboard satisfy the requirements of a maximum flux for the micro-pump, and the synthetic-jet-based micro-pump mass flow rates at the inlet and the outlet both are inimitable and invariable positive. The micro-pump flux can be adjusted efficiently by the dividing-clapboard, and the control rule can satisfy the claims of adjusting the position of dividing-clapboard.In order to resolve the limitations of the continuous flow micro-pumps, an ideal of employing the reciprocating micro-pumps to provide a steady flow is presented. A DSJA-based continuous flow micro-pump is put forward originally; it consists of a DSJA, a dividing-clapboard, a mesh filter, and a baffle plate between the two exits of the DSJA. The DSJA micro-pumps with baffle plates in different heights are simulated. Results show the DSJA micro-pumps transport steady flow efficiently and the fluctuation range is less than 1%. The height of the baffle plate affects the efficiency of the DSJA micro-pumps. The criterion of"self-support"and the characteristic of the saddle point can direct the designing of the baffle plate.