High-Speed Imaging of Drops and Bubbles

发布时间: 2015-11-23 02:44:00  
Marie-Jean Thorav博士
ICAM, Xi'an Jiaotong University, China
时  间:11月30日 (周一)下午3:00—4:00
地  点:工学院1号楼210会议室
Drops and bubbles constitute the fundamental form of interfacial fluids at small scales, due to the action of surface tension. Therefore, understanding their dynamics has a wide range of implication, in nature and the industry, including inkjet printing, combustion, climate modelling and cooling technologies. One of the challenges is to capture their extremely fast motion at small scale. With the recent progresses in high-speed imaging techniques, it has become possible to explore a new world at frame rates up to 10 million frames per second. We combine experimental observations with large parallel numerical simulations to study these dynamics.
* We first focus on new phenomena responsible for splashing and air entrapment during drop impact on a liquid pool. At high impact velocities, splashing is produced by the breakup of a liquid sheet oscillating between the drop and the pool. It also produces a row of bubbles rings, predicted numerically and observed experimentally. At low impact velocities, a myriad of micro-bubbles can be produced by the breakup of an air film stretching between the drop and the pool. At intermediate velocities, a bubble larger than the drop can be entrapped due to a vortex ring produced during impact.
* Then we look at the impact of a drop of nano-particles dispersion on a solid surface. At low impact velocities, the droplet spreads on a smooth glass surface. By increasing the impact velocity, a first transition is observed towards splashing. However, when the impact velocity is further increased, a second transition is observed, above which no splashing is observed. We give some possible interpretations of this surprising behaviour, never observed before for other liquids.
* Finally, we look at the coalescence of bubbles. When two bubbles are brought together, they merge and tend to form one larger bubble. However, counter-intuitively this coalescence process can leave a satellite behind under some conditions: this is called partial coalescence. This process is also observed for the coalescence of liquid drops. We continuously change the pressure of the gas bubble in a high pressure chamber to bridge the gap between the partial coalescence of bubbles and drops.
Marie-Jean Thoraval obtained Master degrees from Ecole Polytechnique (Paris, France) in 2007 and Supaéro (Toulouse, France) in 2008, and his PhD in Fluid Mechanics from KAUST (Saudi Arabia) in 2013. He then worked as a postdoc at the Physics of Fluids group in the University of Twente (The Netherlands). He is now Tenure-track PI at Xi'an Jiaotong University since 2015, where he received the Young Talent Support Plan B of the university.