Dynamic characteristics comparison between non-spherical hydrodynamic cavitation bubbles and spark-induced cavitation bubbles.

In this work, we develop a new experimental approach using the whipping motion of a large-deformation flexible body in water, which achieves stable generation of single non-spherical hydrodynamic cavitation bubbles in a quiescent environment. We also systematically compare the dynamic characteristics between whipping-induced and spark-induced cavitation bubbles. Whipping-induced bubbles exhibit obvious daughter bubble shedding during evolution, with rough surfaces covered by protruding sub-bubbles and implosive rebound during collapse. In contrast, spark-induced bubbles evolve nearly spherically with smooth surfaces and negligible daughter bubble shedding. Whipping-induced bubbles show significant temporal asymmetry between growth and collapse: their growth duration is much longer than the collapse time, unlike spark-induced bubbles, which display nearly symmetric evolution. Regarding shock wave characteristics, whipping-induced bubbles produce multi-sequential shock waves upon collapse, with pressure signals consisting of a main peak plus multiple low-amplitude waves. Spark-induced bubbles, however, emit isolated spherical shock waves with concentrated energy and high peak pressure. Whipping-induced bubbles have a much lower content of non-condensable gas, resulting in fewer oscillations, shorter lifetime, and less residual gas after collapse. The effects of liquid conductivity, viscosity, and temperature on the evolution of both bubble types are also investigated. This study provides a new approach for the experimental investigation of non-spherical hydrodynamic single bubbles and lays a theoretical foundation for clarifying their applicable ranges in single-bubble research.