Shock waves from non-spherical cavitation bubbles

Abstract

We present detailed observations of the shock waves emitted at the collapse of single cavitation bubbles using simultaneous time-resolved shadowgraphy and hydrophone pressure measurements. The geometry of the bubbles is systematically varied from spherical to very non-spherical by decreasing their distance to a free or rigid surface or by modulating the gravity-induced pressure gradient aboard parabolic flights. The non-spherical collapse produces multiple shocks that are clearly associated with different processes, such as the jet impact and the individual collapses of the distinct bubble segments. For bubbles collapsing near a free surface, the energy and timing of each shock are measured separately as a function of the anisotropy parameter $\zeta$, which represents the dimensionless equivalent of the Kelvin impulse. For a given source of bubble deformation (free surface, rigid surface or gravity), the normalized shock energy depends only on $\zeta$, irrespective of the bubble radius $R_0$ and driving pressure $\Delta p$. Based on this finding, we develop a predictive framework for the peak pressure and energy of shock waves from non-spherical bubble collapses. Combining statistical analysis of the experimental data with theoretical derivations, we find that the shock peak pressures can be estimated as jet impact-induced hammer pressures, expressed as $p_h=0.45{\left(\rho c^2\Delta p\right)}^{1/2}{\zeta }^{-1}$ at $\zeta >10^{-3}$. The same approach is found to explain the shock energy quenching as a function of ${\zeta }^{-2/3}$.

Accepted for publication in Physical Review Fluids

References in corpus (5)

• Scaling laws for jets of single cavitation bubbles
• Shock formation in the collapse of a vapor nano-bubble
• The Quest for the Most Spherical Bubble
• Energy partition at the collapse of spherical cavitation bubbles
• Analytical Approximations for the Collapse of an Empty Spherical Bubble

Cited by in corpus (1)

• Luminescence from cavitation bubbles deformed in uniform pressure gradients