Observations of shockwave phenomena in dielectric liquids: comparison between Lens-Type and Mirror-Type schlieren photography technologies

In this paper, Lens-Type and Mirror-Type schlieren photography were used in observing shockwave phenomena associated with streamer propagation. The resolutions of shockwave propagation velocity and streamer pressure profile were compared to indicate the optimal photography in shockwave observation under different test conditions. Shockwave phenomena in a gas-to-liquid oil were observed by applying standard lightning impulse voltages on a 25 mm Needle-plane electrode configuration. Lens-type schlieren system was assembled with a LED collimator, convex lens of 40mm diameter and 80mm focal length and a Razor blade. Mirror-type schlieren system was assembled with a LED point light source, a reflecting mirror of 200mm diameter and 750mm focal length and a Razor blade. Shockwave phenomena from streamer initiation stage to breakdown stage are captured by using a high-speed camera. Velocities of shockwave at different propagation times was observed, and pressure of shock wave was calculated by Hugoniot equation, which utilizes the relation between the shock pressure and its propagation velocity. The results show that both mirror-type schlieren photography and Lens-type schlieren photography are good measures for observing the phenomena of flow shock wave in dielectric liquids.