Rayleigh-Taylor instabilities in a collapsing bubble

Bubbles filled with gas or vapour can emit light when collapsing violently in a surrounded liquid upon strong excitation. This is the case in single bubble sonoluminescence (SBSL) which is a light emission phenomenon of stable oscillating bubble in liquid irradiated by a periodic ultrasound wave field. Because of enormous compression rates, high temperatures occur inside the bubble, in some cases reaching up to 50000K, with a high concentration of energy. But there are limits that bound the possibilities to go beyond this point imposed by different kinds of instabilities. The Rayleigh-Taylor instability is present in this case and occurs when the lighter gas inside the bubble is accelerated into the heavier fluid and only acts on very short time scales on the order of nanoseconds. Numerical simulations are at present the only tool to provide the means to determine the boundary limits of this instability in the parameter space of the problem. The purpose of the current work is to find optimum conditions to move forward the boundary imposed by RT instability with the goal of achieving maximum concentration of energy inside the bubble. The work performed at NTNU will continue the development of an existing model already developed at the Cavitation Laboratory at Balseiro Institute. The next step will be to compute the shape instability boundary incorporating the effects of vorticity to the model and solve the spatial problem. The new development will include the implementation of spectral methods for solving the resulting system of equations. After the new implementation, testing the numerical scheme with present data will take place. Finally, we will make a parametric study changing the properties of the liquid and the gas. As result we expect to compute the instability boundary in a properly space parameters for each case. The research project will be hosted at the Dep. of Energy and Process Engineering, NTNU, for a period of 3 months beginning in January 2011.