000231960 001__ 231960
000231960 005__ 20190917060529.0
000231960 02470 $$2urn$$aurn:nbn:ch:bel-epfl-thesis8089-3
000231960 02471 $$2nebis$$a11065496
000231960 0247_ $$a10.5075/epfl-thesis-8089$$2doi
000231960 037__ $$aTHESIS
000231960 041__ $$aeng
000231960 088__ $$a8089
000231960 245__ $$aCollapse phenomena of deformed cavitation bubbles
000231960 269__ $$a2017
000231960 260__ $$bEPFL
000231960 260__ $$c2017
000231960 300__ $$a116
000231960 336__ $$aTheses
000231960 502__ $$aProf. Jean-François Molinari (président) ; Dr Mohamed Farhat (directeur de thèse) ; Prof. François Gallaire, Prof. Joseph Katz, Prof. Claus-Dieter Ohl (rapporteurs)
000231960 520__ $$aCavitation bubbles are a topic of long-standing interest owing to the powerful phenomena associated with their collapse. Their unique ability to focus energy typically causes damage in hydraulic machinery (turbines, pumps, propellers, ...) but, if managed correctly, can also be beneficial in numerous applications such as cleaning practices and biomedical sciences. Here the complex problem of cavitation, often multi-scale both in time and space, is reduced to a simplified case study of the collapse of a single, initially spherical bubble. We study the bubble's energy distribution into its distinct collapse phenomena, namely the micro-jets, shock waves and luminescence, and aim to quantify and predict how such a distribution is affected by the bubble's deformation. Combining experiments with statistical analysis, numerical simulations and theoretical models, we seek to quantify and predict the key properties characterising each of the collapse phenomena. The deformation of bubbles is characterised by the liquid micro-jets formed during their non-spherical collapse. A unified framework is proposed to describe the dynamics of such jets, driven by different external sources, through an anisotropy parameter $\zeta$, which represents a dimensionless quantity of the liquid momentum at the bubble collapse (Kelvin impulse). The bubbles are carefully deformed in variable gravity aboard European Space Agency parabolic flights or by introducing surfaces nearby. Through high-speed visualisation, we measure key quantities associated with the micro-jet dynamics (e.g. jet speed, impact timing), which, upon normalisation, reduce to straightforward functions of $\zeta$. This is verified by numerical simulations based on potential flow theory. Below a certain threshold, all of these functions can be approximated by useful power laws of $\zeta$ that are independent of the micro-jet driver. For bubbles collapsing near a free surface, we identify and measure the shock waves generated through distinct mechanisms, such as the jet impact onto the opposite bubble wall and the individual collapses of the remaining bubble segments. The energy carried by each of these shocks is found to vary with $\zeta$. We find that for bubbles that produce jets, the shock wave peak pressure may be approximated by the jet-induced water hammer pressure as a function of $\zeta$. Following such an approximation, we also develop a semi-empirical model to explain the shock energy variation with $\zeta$. Finally, an innovative luminescence detection system is built to overcome the challenge of measuring the spectra (300-900nm) of the weak, small, rapid and migrating flash light from individual bubble collapses. We find an approximately exponential quenching of the luminescence energy as a function of $\zeta$. Surprisingly, the blackbody temperature of luminescence does not vary with $\zeta$. Multiple peaks are measured within a time frame of approximately 200ns, implying non-uniform gas compression during the collapse. Overall, these results help in predicting bubble collapse characteristics in known pressure fields and can be useful for numerical benchmarking.
000231960 592__ $$b2017
000231960 6531_ $$acavitation
000231960 6531_ $$abubble
000231960 6531_ $$acollapse
000231960 6531_ $$amicro-jet
000231960 6531_ $$ashock wave
000231960 6531_ $$aluminescence
000231960 6531_ $$aFNS
000231960 6531_ $$aFlash and Splash
000231960 700__ $$g238857$$aSupponen, Outi$$0247876
000231960 720_2 $$e"dir."$$aFarhat, Mohamed
000231960 8564_ $$zn/a$$yn/a$$uhttps://infoscience.epfl.ch/record/231960/files/EPFL_TH8089.pdf$$s7301762
000231960 8560_ $$fmohamed.farhat@epfl.ch
000231960 909C0 $$xU10309$$0252135$$pLMH
000231960 909CO $$pthesis$$pthesis-bn2018$$pDOI$$ooai:infoscience.tind.io:231960$$qDOI2$$qGLOBAL_SET$$pSTI
000231960 917Z8 $$x108898
000231960 918__ $$dEDME$$cIGM$$aSTI
000231960 919__ $$aLMH
000231960 920__ $$b2017$$a2017-11-3
000231960 970__ $$a8089/THESES
000231960 973__ $$sPUBLISHED$$aEPFL
000231960 980__ $$aTHESIS_LIB