An experimental study on the collapse of an air-filled cylindrical cavity under dynamic loading

Fluid mechanics;Multiphase;Bubbles;Bubble collapse;Cavitation;Wave-bubble interaction;Shadowgraph;Particle Image Velocimetry (PIV)

Shpuntova, Galina V

关键词: Fluid mechanics;    Multiphase;    Bubbles;    Bubble collapse;    Cavitation;    Wave-bubble interaction;    Shadowgraph;    Particle Image Velocimetry (PIV);   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/102451/SHPUNTOVA-DISSERTATION-2018.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

A model system was designed and investigated experimentally to gain insight into the interactions of an air-filled cylindrical bubble immersed in hydrogel, a compliant boundary, and a transient loading wave. This combination is an analog of processes that occur in biomedical applications such as shockwave lithotripsy. No-boundary, rigid boundary, and two-boundary cases were also investigated. A transient pressure wave of 20~MPa peak magnitude generated by projectile impact was used to initiate bubble collapse. Ultra high-speed video recordings of the process showed the development of a re-entrant jet characteristic of asymmetric bubble collapse in the no-boundary case, but less frequent occurrence of this behavior in cases with boundaries. Void interface velocity in excess of 200~m/s was detected, which is sufficient to cause pressures in the hundreds of megapascals and possibly damage tissues. However, an alternative damage mechanism is also proposed based on the significant deformation of the upstream boundary during the collapse time.Flowfield data for all cases were acquired by a particle image velocimetry technique to elucidate the causes of boundary deformation, the suppression of jet formation, and the extreme velocities on the upstream void interface. An analytical model for the flow was developed to describe these flowfields, incorporating three components: the free-stream flow, a source flow, and a doublet flow. Parameters of the model were determined by fitting to data. The model represented the data to within 5~m/s on average---this was approximately equal to the 1-pixel PIV system noise threshold, and 5\% of the maximum flowfield velocity. The variation of model parameters over the course of the collapse was investigated to give the model predictive as well as descriptive value. The source strength agreed well with predictions based on symmetrical collapse relations. The doublet strength was consistent with the generation of vorticity on the bubble boundary due to interaction with a weak shock.