Jet reversal in mixed bubbles induced by competing internal and boundary Kelvin impulse

Abstract

High-pressure bubbles drive strongly directed re-entry jets that govern near-field hydrodynamic loading, cavitation damage, and jet-assisted applications. Jet steering is commonly attributed to external pressure gradients and boundary-induced asymmetry. Heterogeneous bubble interiors are herein shown to provide an additional, internal control route. With an extended potential-flow formulation and multimaterial simulations, the collapse of a mixed-gas bubble (air and byproducts) in an ideal liquid without buoyancy is investigated. A late-stage end-cap compression disparity produces an internal Kelvin-type impulse, Iint. It competes with the wall-induced external impulse, Iext, and can reverse the jet direction at sufficiently large stand-off distance γ. The dimensionless anisotropy parameters ζint and ζext are introduced to quantify the internal pressure-dipole forcing and the boundary contribution, the latter decaying rapidly with γ. This yields a compact scalar relation in which the jet regime is determined by ζtot=ζext+ζint: ζtot≪0 produces wall-jets, ζtot≈0 produces Worthington-like jet pairs (0≤|ζtot|≤0.003 027 for this work), and ζtot≫0 produces reverse-jets. The resulting impulse-based framework extends classical Kelvin-impulse theory to mixed-gas bubbles with internal–external competition and provides a physics-based basis for active jet control via engineered internal enrichment.