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This paper aims to experimentally study the external flow characteristic of an isolated two-dimensional synthetic jet actuator undergoing diaphragm resonance.

The resonance frequency of the diaphragm (40 Hz) depends on the excitation mechanism in the actuator, whereas it is independent of cavity geometry, excitation waveform and excitation voltage. The velocity response of the synthetic jet is influenced by excitation voltage rather than excitation waveform. Thus, this investigation selected four different voltages (5, 10, 15 and 20 V) under the same sine waveform as experiment parameters.

The velocity field along the downstream direction is classified into five regions, which can be obtained by hot-wire measurement. The first region refers to an area in which flow moves from within the cavity to the exit of orifice through the oscillation of the diaphragm, but prior to the formation of the vortex of a synthetic jet. In this region, two characteristic frequencies exist at 20 and 40 Hz in the flow field. The second region refers to the area in which the vortices of a synthetic jet fully develop following their initial formation. In this region, the characteristic frequencies at 20 and 40 Hz still occur in the flow field. The third region refers to the area in which both fully developed vortices continue traveling downstream. It is difficult to obtain the characteristic frequency in this flow field, because the mean center velocities (ū) decay downstream and are proportional to (x/w)^−1/2 for the four excitation voltages. The fourth region reveals variations in both vortices as they merge into a single vortex. The mean center velocities (ū) are approximately proportional to (x/w)⁰ in this region for the four excitation voltages. A fifth region deals with variations in the vortex of a synthetic jet after both vortices merge into one, in which the mean center velocities (ū) are approximately proportional to (x/w)⁻¹ in this region for the four excitation voltages (x/w is the dimensionless streamwise distance).

Although the flow characteristics of synthetic jets had reported for flow control in some literatures, variations of flow structure for synthetic jets are still not studied under the excitation of diaphragm resonance. This paper showed some novel results that our velocity response results obtained by hot-wire measurement along the downstream direction compared with flow visualization resulted in the classification of five regions under the excitation of diaphragm resonance. In the future, it makes valuable contributions for experimental findings to provide researchers with further development of flow control.

This study aims to design and test some fixed‐wing micro aerial vehicles (MAV).

The MAV wing planform in this study was designed based on previous results and the need to reduce the weight of the MAV. The MAV had a wing planform with a 6 percent Gottingen‐329 camber airfoil, a 20° swept‐back leading edge and a straight trailing edge. The fuselage was designed to contain a motor, an electronic control system and a video camera with a built‐in transmitter. The battery was located outside the fuselage to trim the center of gravity and enable the battery to be changed easily when it has run out. Two exaggerated vertical stabilizers were installed to prevent the MAV from rolling. The materials, the power plant and the electronics used to fabricate the MAV herein were either the lightest or the smallest from that could be obtained off‐the‐shelf. Since, MAVs should be expendable, the cost was kept under US$250 (including the cost of an onboard video camera system, which costs US$170).

Flight tests were performed following fabrication. The MAV was launched by hand, flew within a radius of 30 ∼ 50 m, and eventually glided to a grassy ground. The flight was stable and the quality of the downlink video was acceptable for surveillance purpose. The MAVs presented in this work were proven to have successful designs.

MAVs were successfully designed herein based on previous results. The materials and the fabrication processes were carefully selected and tested, to keep the mass of a flyable MAV under 65 g, while ensuring it has sufficient structural strength. The cost was reduced to US$250, making the MAV truly expendable.

Low combustion completeness has been the main defect of hybrid rockets. The present study tries to address the problem by bringing up the setup of the precombustion zone, which do not increase the manufacture cost and complexity.

A precombustion zone can provide a space for the liquid oxidizer to vaporize before entering the combustion zone, and prevents the endothermic effect of liquid oxidizer which can block the chemical reaction as well as the fuel regression. Therefore, this design is expected to raise the combustion completeness. The numerical simulation focuses on the flow field inside a cylindrical hybrid combustor. The distribution of temperature, combustion mode, mass fraction of reactants, velocity, combustion completeness, and solid‐fuel regression rate are presented.

With the setup of prevaporized zone of appropriate length, the upstream separation bubble which is unobvious for the case with no prevaporized zone can increase the mixing of reactants, and then increases the combustion completeness. Besides, the radial temperature distribution is more uniform. But when the length of prevaporized zone exceeds about one fourth of the combustor length, due to no enough space for the reactants to react, the combustion completeness begins to decrease and the radial temperature distribution becomes uneven. Therefore, a prevaporized zone with about 24 per cent of the combustor length can have optimum combustion completeness in the present study.

This study provides a useful design to raise the combustion completeness of a traditional hybrid rocket. However, the manufacture cost and complexity are not increased. So the results can be a good reference for the hybrid rocket designers.