Papers by Keyword: Shadowgraph

Abstract: In the application of sprays produced by an atomizer, spray angle is one of key performance parameters. A larger spray angle is often required in providing a better spray dispersion. Swirl effervescent atomizer is one of the existing atomizers with the capability to produce a large spray angle. The formation of spray angle from this atomizer however is hardly understood. A newly-designed swirl effervescent atomizer was developed and tested with different swirl-generating vane angle in order to understand the swirl intensity effect on the spray angle. Experiments were carried out based on a cold flow test approach using water as the working fluid and nitrogen gas as the atomizing agent. High-speed shadowgraph technique was deployed to record the resultant sprays produced. Video recordings, acquired using a high-speed video camera, were converted to a sequence of images for further analysis using an image processing software. It was found that the spray angle increases with the swirl-generating vane angle. Specifically, the spray angle shows an abrupt increase for the case of swirl-generating vane angle changing from 30° to 45° but visualizes only a gradual increase in the case of swirl-generating vane angle changing from 45° to 60°.

Abstract: The expansion property of an infrared CO₂ laser produced air plasma is characterized using a high-speed imaging shadowgraph technique. The shadowgraphs were taken by a time-gated intensified charge-coupled device at various delay times after single pulses induced gas breakdown. We examined five incident laser energy of 180, 240, 345, 420 and 600 mJ induced air breakdown at the pressure of atmospheric and 10⁴ Pa. A shock wave produced by laser induced breakdown was also observed and its speed was measured as a function delay time between the breakdown and the shadow imaging under different air pressure. The experimental results indicated that the radial and axial shock wave front evolutions showed similar behavior, which increased fast with delay time at early stage and slowly at later stage. The propagation speed of the wavefront was about 2 cm/μs at the initial stage of breakdown, and then decreased very quickly. The propagation speed under low air pressure was higher than that of gases under high pressure and the spark sustained less time at lower pressure. The size of laser induced air spark increased with incident laser energy but not simple linear relationships.

Abstract: Shadowgraph is an important method to obtain the flight characteristics of high-speed object, such as attitude and speed etc. To get the contour information of objects and coordinates of feature points from shadowgraph are the precondition of characteristics analysis. Current digital shadowgraph system composed of CCD camera and pulsed laser source is widely used, but still lack of the corresponding method in image processing. Therefore, the selection of an effective processing method in order to ensure high effectiveness and accuracy of image data interpretation is an urgent need to be solved. According to the features of shadowgraph, a processing method to realize the contour extraction of high-speed object by adaptive threshold segmentation is proposed based on median filtering in this paper, and verified with the OpenCV in VC environment, the identification process of the feature points are recognized. The result indicates that by using this method, contours of high-speed objects can be detected nicely, to combine relevant algorithm, the pixel coordinates of feature points such as the center of mass can be recognized accurately.

Abstract: This paper describes the characteristics of supersonic non-Newtonian liquid jets injected in ambient air. The main focus is to visualize three types of time-independent non-Newtonian liquid jet and to describe their behaviors. Moreover, comparisons between their dynamic behaviors with Newtonian liquid jet are reported. The supersonic liquid jets are generated by impact driven method in a horizontal single-stage power gun. Jets have been visualized by the high speed digital video camera and shadowgraph method. Effects of different liquid types on the jet penetration distance, average jet velocity and other characteristics have been examined. From shadowgraph images, the unique dynamic behaviors of each non-Newtonian liquid jets are observed and found obviously different from that of the Newtonian liquid jet. The maximum average jet velocity of 1,802.18 m/s (Mach no. 5.30) has been obtained. The jet penetration distance and average velocity are significantly varied when the liquid types are different.

Abstract: This paper describes the study of high-speed liquid jets injected in air from an orifice. The main focus is to study the effect of different liquid properties on the characteristics of the high-speed liquid jets injected in ambient air. The high-speed liquid jets are generated by the impact of a projectile, which known as impact acceleration method, launched in a horizontal single-stage power gun (HSSPG). The conical nozzle of 30° angle with the orifice diameter of 0.7 mm was used to generate the jets. The characteristics of high-speed jets were visualized by the high-speed digital video camera with shadowgraph optical arrangement. From the shadowgraph images, the jet formation, atomization, vaporization and shock waves were obviously observed. The maximum averaged velocity of water, alcohol, n-hexane, chloroform and glycerin jets is estimated to be 1,669.03 m/s, 1,548.59 m/s, 1,420.44 m/s, 1,204.46 m/s and 1,496.97 m/s, respectively. That effect on the maximum penetration distance of the water jet is longer than that of all jets. Surface tension and latent heat are the significant physical property for jet formation, while density, kinematics viscosity and heat capacity are not.

Abstract: This study is to measure the impact pressure of high-speed water jet injected in water at the stand-off distance from the nozzle exit. The high-speed water jets are generated by the impact of a projectile, which known as impact acceleration method, launched by Horizontal Single Stage Power Gun. The maximum averaged jet velocity of about 374.24 m/s in water was generated in this experiment. The impact pressure of high-speed water jet in water at the stand-off distance 15, 20, 30 and 40 mm from the nozzle exit was measured by the PVDF pressure sensor. Moreover, the impact phenomena of the jet were visualized by a high-speed video camera with shadowgraph optical arrangement. From the pressure sensor, two peak over-pressures are always observed in this experiment. From visualization, it was found that the two peak over-pressures of 24 GPa and 35 GPa at x = 15 mm were generated by the jet and the bubble impact, respectively. The peak over-pressure decreases exponentially as the stand-off distance between the PVDF pressure sensor to the nozzle exit increases. Moreover, the jet and the bubble impact on the PVDF pressure sensor, shock waves, and bubble deformation were obviously observed in this study.