Modeling of the Thermal Behavior Inside a Bubble

Abstract

Cavitation occurs by the sudden expansion and the volumetric oscillation of bubble nuclei in the water due to the ambient pressure change. The size of bubble nuclei is O(10mm) and the thermal damping effects on the bubble motion is dominant in comparison with the acoustic and viscous damping effects. Because the thermal damping effect strongly depends on the thermal phenomena inside the bubble, it is important to simulate the detailed thermal behavior inside the bubble. The full DNS (Matsumoto and Takemura (1994) and Takemura and Mastumoto (1994)) is the most useful method to obtain the detailed structure. However, since it requires a long computational time to conduct the full DNS, a simple modeling for the internal thermal behavior is required. As we have known that there are many simple models for calculating the bubble oscillation such as the Rayleigh-Plesset equation etc. Nevertheless, most of previous works have assumed the thermal process of content inside the bubble to be adiabatic or isothermal and have neglected the thermal damping effect. In the present study, a simple model of the thermal behavior inside a spherical bubble is developed coupling with the Rayleigh-Plesset equation. The behavior of a spherical bubble in an acoustic field is numerically obtained by the full DNS, the present model and the conventional ones under adiabatic and isothermal assumptions.