Numerical Investigation on the Flow Instability of Dispersed Bubbly Flow in a Horizontal Contraction Section

Abstract

Dispersed bubbly flow is important to understand when working in a wide variety of hydrodynamic engineering areas; the main objective of this work is to numerically study bubble-induced instability. Surface tension and bubble-induced turbulence effects are considered with the momentum and k-ω transport equations. Steady dispersed bubbly flow is generated at the inlet surface using time-step and user-defined functions. In order to track the interface between the liquid and gas phases, the volume of fraction method is used. Several calculation conditions are considered in order to determine the effects of bubble diameter, bubble distribution, bubble velocity and bubble density on flow instability and void fraction. The void fraction of the domain is set to no more than 0.5% under different bubbly (micro/small) flow conditions; and the order of magnitude of the Reynolds number is 106. Results from the simulation indicate that velocity fluctuation induced by bubble swarm increases with increasing bubble diameter. Bubble density and bubble distribution seem to have a complex influence on flow instability. Bubble-induced turbulence results indicate that small bubbles produce a significant disturbance near the boundary region of bubble swarm; this indicates that induced bubble swarm has a potential capability of enhancing heat and mass transfer in the velocity boundary layer. Results from this study are useful for two-phase flow, bubble floatation and other hydrodynamic engineering applications.