A computational fluid dynamics based numerical model framework was proposed to simulate two-phase flows with interfacial structures of multiple length scales, e.g. one large bubble and many small dispersed bubbles. In this numerical method, the large bubble is tracked using a volume of fluid (VOF) method, and the small bubbles are tracked using a discrete particle method (DPM). The couplings among the continuous liquid/gas phases and the discrete small bubble phases are accounted for To evaluate the model performance, this model was applied to simulate the interaction between a large bubble and many suspended small bubbles in 2D vertical channels under different bubble shape regimes. It is found that the small dispersed bubbles may impose important effects on the rising behavior of the large bubble. The simulations have revealed both hindrance and acceleration effects of small bubbles on the rising of large bubble, which agrees with experimental observations qualitatively. (C) 2014 Elsevier Ltd. All rights reserved.