Tubular jet generation by means of a pressure pulse induced by an eddy-current actuator

The generation and the evolution of tubular jets is studied experimentally and compared to numerical results from a boundary integral code. The jets are created at the free surface above a liquid column of purified water. An eddy-current actuator driven by a high voltage capacitor bank is used to create a pressure pulse with a duration of about $100~\mu\mathrm{s}$ and varying amplitude of up to $70~\mathrm{bar}$. The pressure pulse travels in the vertical water column of length 1 m before hitting the free surface in a capillary tube of $4-8~\mathrm{mm}$ in diameter. The process of jet formation is captured using high-speed imaging at up to $60~\mathrm{kHz}$, while the pressure pulse is recorded by two PVDF transducers at $20~\mathrm{MHz}$. The recordings and the numerical simulations enable us to study the effect of the control parameters on the jet velocity (which can reach up to $50~\mathrm{m/s}$) and the mass flow. Namely, we study the effect of the applied acoustic power of the pressure pulse and the initial curvature of the free surface.