Dynamics of cavitation bubble generated by low voltage discharge under hypobaric conditions

A combined experimental and theoretical study is conducted on cavitation bubble dynamics under hypobaric conditions, focusing on the collapse mechanisms of bubbles with radii of ̃O(10–25) mm generated by low-voltage discharge (LVD). Experiments are performed over ambient pressures of 0.02–0.1 MPa to identify conditions for jet-free neutral collapses, where buoyancy effects remain negligible. In the first oscillation cycle, reduced ambient pressure delays bubble evolution, yielding a larger maximum radius and longer collapse time while preserving spherical geometry, indicative of inertia-dominated collapse. In the second cycle, decreasing ambient pressure enhances surface instabilities, and buoyancy-induced asymmetry intensifies near collapse, producing stronger upward-directed jets, whereas at 0.05 MPa, jet formation is suppressed and a neutral collapse is observed. Theoretical interpretation is limited by the loss of early radius and velocity data from overexposure in LVD. These are recovered using discrete weighted orthogonalization (DWO), enabling reconstruction of radius and wall-velocity histories with orthonormal polynomial expansions. Internal pressure is estimated using an inverse Gilmore model and expressed in virial form, fitted separately for the expansion and collapse phases to capture thermodynamic asymmetry. The virial model is coupled with the Gilmore equation for forward simulations, along with Noble–Abel stiffened-gas equation of state for the liquid phase to predict the temporal evolution of bubble radius, internal pressure, and temperature. This DWO–Gilmore–Virial approach successfully reproduces radius–time histories under hypobaric conditions with high accuracy, enabling deeper insights into the governing bubble dynamics. Internal pressure and temperature estimates show consistency with Rayleigh collapse predictions at specific polytropic exponents. The framework provides a robust tool for applications in underwater blasts, medical therapy, and bubble propulsion.