Surface dielectric barrier discharge (SDBD) is an important form of atmospheric discharge. The present study uses particle image velocimetry to investigate the influence of the duty cycle and pulse frequency on the flow field of plasma-induced jets and turbulent flow features for high-frequency high-voltage AC actuation under a low pressure of 7 kPa. The results prove that the SDBD plasma induces a suction flow and a horizontal tangential flow. Both the duty cycle and the pulse frequency have significant effects on the induced flow field. With the increasing duty cycle, the length and velocity of the jets increase linearly, the exit angle increases, and the Reynolds number of the tangential jet increases. The tangential jet transitions from turbulent to laminar flow as the duty cycle increases. As the pulse frequency increases, both the length of the tangential jet and the exit angle decrease gradually, and this trend accelerated near 30 Hz. The Reynolds number of the tangential jet increases to a maximum and then decreases with the increasing pulse frequency, with a peak near 50 Hz. The pulse frequency has little effect on the velocity of the jets or the turbulent flow characteristics of the tangential jet. A low duty cycle and a low pulse frequency should be adopted to increase the turbulent flow area and jet size to achieve a better actuation effect.
There is a lack of understanding of the spray characteristics of gas-centered swirl coaxial (GCSC) injectors during self-pulsation occurs. Therefore, the self-pulsation of a GCSC injector was investigated experimentally in this study. Experiments were conducted at atmospheric pressure with filtered water and dried air supplied through a propellant feed system. A back-lighting high-speed photography technique was used to capture unsteady spray features. A laser-based particle size analyzer (LPSA) was used to measure the size of the droplets in the spray. The effects of recess and gas-liquid ratio on spray self-pulsation were analyzed. It was found that the recess of the injector strongly determines the spray pattern. When spray self-pulsation occurs without recess, both the center and periphery of the spray oscillate. With an increase in the mass flow rate of the gas, the boundary between the center and the periphery of the spray becomes more noticeable. Meanwhile, small droplets in the spray center oscillate, with the periphery of the spray being characterized by a periodic “shoulder.” Under the same operating conditions but with a small recess (2 mm), the spray adheres to the injector faceplate. With a larger recess (7 mm), when spray self-pulsation occurs, the spray periodically forms “shoulder” and “neck,” similar to the behavior of self-pulsation in a liquid-centered coaxial injector. Therefore, it can be concluded that spray self-pulsation enhances atomization at the center of the spray to a certain extent. However, atomization becomes worse in the periphery with an oscillating spray.
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