Numerical simulation of micro-bubble drag reduction of an axisymmetric body using OpenFOAM

Abstract

The two-phase micro-bubble flow over an axisymmetric body is investigated using the OpenFOAM framework. The numerical model consists of an Eulerian-Eulerian two-fluid model with closure relationships for the interfacial momentum transfer to capture the multiphase flow, a standard k – e model for the continuous phase and one turbulence model inside the OpenFOAM for the dispersed phase. The bubble sizes are calculated based on the solution of the transport equation of the interfacial area density. The simulations in this work are carried out with different air injection rates and different flow velocities. The effects of bubble size on drag reduction are analyzed. The numerical results are compared against some available experiments and other numerical simulations. The numerical results indicate that the airflow rate and air volume fraction within the boundary layer near the body play important roles in micro-bubble drag reduction. The frictional drag reduction effect by micro bubbles is larger for lower water speed, and the presence of the micro bubbles can increase the pressure resistance of the body. Drag reduction rates are generally higher when the bubble diameter is smaller.