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arXiv · 1708.04049

Shock waves from non-spherical cavitation bubbles

Outi Supponen·Danail Obreschkow·Philippe Kobel·Marc Tinguely·Nicolas Dorsaz·Mohamed Farhat
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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 $ζ$, 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 $ζ$, irrespective of the bubble radius $R_{0}$ and driving pressure $Δp$. 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 $p_{h} = 0.45\left(ρc^{2}Δp\right)^{1/2} ζ^{-1}$ at $ζ> 10^{-3}$. The same approach is found to explain the shock energy quenching as a function of $ζ^{-2/3}$.

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Outi Supponen, Danail Obreschkow, Philippe Kobel, Marc Tinguely, Nicolas Dorsaz, Mohamed Farhat. 2017-08-14. Shock waves from non-spherical cavitation bubbles. https://doi.org/10.1103/physrevfluids.2.093601

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