Author:
Ghigliotti Giovanni 
In a high speed liquid flow, local pressure can vary. If the pressure drops below vapor pressure, the liquid vaporizes and a vapor bubble appears. This is called cavitation. Bubbles are carried away by the liquid flow, and can reach zones where the local pressure is higher; here, bubbles can become instable and implode. This implosion can generate very powerful liquid jets and shock waves, that are able to seriously damage solid materials (turbine blades in hydroelectric power plants, ship propellers…). This phenomenon is called “cavitation erosion”.
In order to better understand cavitation erosion, we study, by means of numerical simulations, the implosion of a single bubble close to a solid wall. The information given by these simulations on the fluid dynamics during the implosion, and the solid wall deformation will help to extend this kind of modelling to a higher number of bubbles and to a bubble cloud, closer to industrial configurations.
The above image shows the density and pressure fields (upper and lower half, respectively) during bubble implosion as a function of time, measured in nanoseconds.
At the beginning of the simulation (0 ns) a shock-wave is generated in order to trigger the bubble implosion, that starts at 275 ns. The bubble is pierced by a liquid jet (316 ns), and a shock wave is spontaneously generated (361 ns); this shock-wave impinges on the solid wall with a pressure close to 1 GPa (10’000 atmospheres).
This work has been realized within Yves Paquette’s PhD thesis, under the supervision of Christian Pellone, Giovanni Ghigliotti, Eric Johnsen (University of Michigan, US), Marc Fivel (SIMAP, Grenoble) and Jean-Pierre Franc.