Hongjoo Jeon

Investigation of Transmission of a Shock Wave Through Thin Films

The aim of the present experimental study is to find physical laws of shock wave transmission through thin films. A horizontal shock tube was used to produce a planar shocks with incident shock Mach numbers of M s = 1.20, 1.34, 1.39, and 1.46 onto thin polyester films. The test section of the shock tube was constructed such that it could hold either a single or multiple layers of 12.7, 25.4, or 50.8 μm thick films. High-speed schlieren photography and high-frequency pressure transducers were used to evaluate the shock wave interactions with the films and the subsequent film breakup. Following incident shock wave impingement, the transmitted and reflected shock waves displayed different strengths, depending on the incident shock Mach numbers and the film thicknesses.

Shock Wave Mitigation Using Liquids

Mitigation of shock waves can be achieved using many different approaches. In this work, an experimental study of passive shock wave mitigation using planar liquid sheets (water or cornstarch suspensions) was completed. The goal was to better understand how planar a liquid sheet could mitigate a planar incident shock wave. The experimental setup consisted of a horizontal shock tube with a square inner cross-sectional area. The shock mitigation effects were studied using high-speed visualization techniques and pressure measurements. Incident shock waves with shock Mach numbers \(M_s = 1.34\) and 1.46 were generated in the shock tube. A square test section frame was designed to hold a rectangular liquid sheet, with a thickness of 5 mm or 10 mm, using plastic membranes and cotton wires to maintain the planar shape and minimize bulge of the liquid sheet. High-speed schlieren and direct high-speed visualization techniques were used to observe the shock wave interaction with the liquid sheets. High-frequency pressure sensors mounted upstream and downstream of the liquid sheet, measured shock wave speed, overpressure, and impulse. Experiments varied by types and thicknesses of liquid sheets and incident shock Mach numbers. Results showed that no transmitted shock wave was observed downstream of the liquid sheets, but compression waves induced by the shock-accelerated liquid coalesced into a shock wave further downstream. A lower peak overpressure and impulse were measured when using thicker liquid sheets, and the cornstarch sheets showed lower peak overpressures and impulses compared to water sheets.

Shock Wave Reflections Over Newtonian and Non-Newtonian Wedges: Experimental Investigation

Shock wave reflections over Newtonian and non-Newtonian fluid wedges were studied to find the transition angle between regular and irregular reflections. To find this transition angle, various experiments were performed for non-rigid wedges at different Mach numbers and incident angles. Newtonian (water) and non-Newtonian (cornstarch–water mixture) fluid wedges were tested and compared. Because the cornstarch–water mixture is a shear-thickening liquid, a different transition angle than for pure water was expected. Results show that the transition angle of water is 2° higher than that of cornstarch–water mixture. This difference is mainly caused by viscous effects.