High speed jet formation by impact acceleration method

Abstract

This paper describes the generation of high-speed liquid jets by the impact acceleration method using a vertical two-stage light gas gun specially designed and constructed for this project at the Interdisciplinary Shock Wave Research Laboratory, Institute of Fluid Science, Tohoku University. Results of pressure measurements and double exposure holographic interferometric visualization and high speed video-recording of shadow graph images of waves propagating in a conically shaped container of liquid are included. In the experiments, an optical fiber pressure transducer of 0.1  mm in diameter and resonant frequency of 100  MHz was used for precise pressure measurements of waves in the container at 300  m/s projectile impacts. To verify the contribution of longitudinal and transversal waves created in metal containers, we used a 10.6 mm × 10.6  mm container of water with thick acrylic observation windows and quantitatively visualized waves by using double exposure holographic interferometry. We found that: (1) longitudinal and transversal waves did exist in the metal parts of the container and also in the acrylic observation windows; (2) before the nozzle flow started, these waves and their reflected waves coalesced with the main impact generated shock wave; (3) the primary jet was driven by pressures of 12.4  GPa caused by the 300  m/s projectile impingement; (4) successive shock reflections inside the container of liquid drove intermittent multiple liquid jets; (5) the contribution of released longitudinal and transversal waves to multiple jet formation is marginal; and (6) negative pressures detected with the optical fiber pressure transducer are attributable to impact flash and have no physical significance.