Interaction of Shock Waves with Water Saturated by Nonreacting or Reacting Gas Bubbles

Abstract

A compressible medium represented by pure water saturated by small nonreactive or reactive gas bubbles can be used for generating a propulsive force in large-, medium-, and small-scale thrusters referred to as a pulsed detonation hydroramjet (PDH), which is a novel device for underwater propulsion. The PDH thrust is produced due to the acceleration of bubbly water (BW) in a water guide by periodic shock waves (SWs) and product gas jets generated by pulsed detonations of a fuel–oxidizer mixture. Theoretically, the PDH thrust is proportional to the operation frequency, which depends on both the SW velocity in BW and pulsed detonation frequency. The studies reported in this manuscript were aimed at exploring two possible directions of the improvement of thruster performances, namely, (1) the replacement of chemically nonreacting gas bubbles by chemically reactive ones, and (2) the increase in the pulsed detonation frequency from tens of hertz to some kilohertz. To better understand the SW-to-BW momentum transfer, the interaction of a single SW and a high-frequency (≈7 kHz) sequence of three SWs with chemically inert or active BW containing bubbles of air or stoichiometric acetylene–oxygen mixture was studied experimentally. Single SWs and SW packages were generated by burning or detonating a gaseous stoichiometric acetylene–oxygen or propane–oxygen mixture and transmitting the arising SWs to BW. The initial volume fraction of gas in BW was varied from 2% to 16% with gas bubbles 1.5–4 mm in diameter. The propagation velocity of SWs in BW ranged from 40 to 580 m/s. In experiments with single SWs in chemically active BW, a detonation-like mode of reaction front propagation (“bubbly quasidetonation”) was realized. This mode consisted of a SW followed by the front of bubble explosions and was characterized by a considerably higher propagation velocity as compared to the chemically inert BW. The latter could allow increasing the PDH operation frequency and thrust. Experiments with high-frequency SW packages showed that on the one hand, the individual SWs quickly merged, feeding each other and increasing the BW velocity, but on the other hand, the initial gas content for each successive SW decreased and, accordingly, the SW-to-BW momentum transfer worsened. Estimates showed that for a small-scale water guide 0.5 m long, the optimal pulsed detonation frequency was about 50–60 Hz.

Editorial for the Special Issue on Droplet-Based Microfluidics: Design, Fabrication, and Applications

“…Frolov et al [ 1 ] explore the interaction of shock waves with bubbly water for generating a propulsive force. The study aims to investigate two potential directions for improving underwater propulsion: (1) replacing chemically inert gas bubbles with chemically reactive ones and (2) increasing the pulsed detonation frequency from tens of hertz to kilohertz.…”

Non-intrusive, imaging-based method for shock wave characterization in bubbly gas–liquid fluids

“…The dynamics of propagating shock waves through single-phase liquids and multiphase liquids in confined geometries have been studied extensively over recent decades (Noordzij and Van Wijngaarden 1974;Jakeman et al 1984;Kameda et al 1998;Tijsseling 2007). Imaging-based methods have been employed to study shock wave characteristics of propagating shock waves through two-phase gas-liquid mixtures (Ando et al 2011;Frolov et al 2022) and laser-induced shock waves (Vogel et al 1996).…”

“…Recently, Gluzman and Thomas (2022) studied unsteady shock wave propagation in aviation fuel cavitation by high-speed imaging and developed an image processing technique, denoted enhanced gradient shadowgraphy, to enhance the appearance of shock waves in the images. Frolov et al (2022) used high-speed imaging to study the shock wave front with non-reacting and reacting gas bubbles for the application in pulsed detonation hydro ramjet, and extracted the shock-induced bubble velocity from the images. Shock wave pressures are commonly measured by high-frequency pressure transducers.…”