Numerical investigation on the bubble size distribution around NACA0015 hydrofoil

Abstract

Two-phase bubbly flows occur widely in nature and are extensively applied in industry. The aeration processes underwater is one type of two-phase bubbly flow that directly impacts on the downstream water quality by reducing the oxygen content in the water. The most important influencing factors for optimization design of Auto-venting turbines (AVTs), for solving the low level of dissolved oxygen (DO) in the discharged downstream water, are the quantity of entrained air, the bubble size distribution resulting from coalescence and breakage processes, and the rate of oxygen transfer from the bubbles. In order to better understand the influencing flow conditions on the bubble size distribution, in this paper a numerical investigation for flow around NACA0015 hydrofoil is carried out. The numerical simulations require the consideration of the dynamic behaviors of two-phase flow and bubbles undergoing coalescence and breakup. For this purpose, the ensemble-averaged mass and momentum transport equations for continuous and dispersed phases are modeled within the two-fluid modeling framework. These equations are coupled with population balance equations (PBE) to aptly account for the coalescence and break-up of the bubbles. The resultant bubble size, normalised velocity and void fraction distributions for different flow conditions including angle of attack (AOA), air-entrainment coefficient, and Reynolds number are presented and discussed. The results show that varying AOA has the most significant impact on the distribution of the bubbles in the wake.