Modeling Laser-generated Cavitation Bubbles

Open Access
Author:
Christian, Cinnamon Maria
Graduate Program:
Mechanical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 05, 2012
Committee Members:
  • Eric Paterson, Thesis Advisor
  • Arnold Anthony Fontaine, Thesis Advisor
Keywords:
  • cavitation
  • laser-generated bubbles
  • CFD
  • multiphase flow
Abstract:
Cavitation erosion is a flow phenomenon where the collapse of cavitating vapor bubbles against a solid surface leads to the erosion of the surface. Cavitation affects various types of turbomachinery, including impeller blades, valves and ship propeller blades, and can affect both the performance and the life-cycle of a machine. A significant amount of research regarding cavitation erosion has focused on the formation and collapse of a single bubble. In experimental research a laser is often used to generate a bubble near a solid surface; mimicking the flow dynamics of cavitation erosion. An experimental setup was devised where a single cavitation bubble was generated using a Nd:YAG laser. A thermal analysis of the formation of a laser-generated cavitation bubble was conducted using the open source CFD package OpenFOAM to model the heating of the water by the laser. The collapse of a laser-generated cavitation bubble was also modeled computationally using a compressible multiphase finite volume method. It was determined experimentally that a typical laser-generated cavitation bubble has a maximum radius on the order of 1 mm. A single bubble with a maximum radius of 1 mm and a collapse time of approximately 190 microseconds was used to model the size and shape of a laser-generated cavitation bubble. Using CFD the collapse of a single bubble in a free field was analyzed and compared to the solution of the Rayleigh-Plesset equation, as well as experimental data. The collapse of a single bubble against a solid wall was then modeled, varying the standoff distance to the wall in order to observe the different bubble dynamics discussed in the literature. The compressible multiphase flow method successfully modeled the dynamics of the bubble collapse; including both the high pressure pulse emitted upon collapse as well as the microjet that forms during collapse and travels from the center of the bubble towards the wall.