Gas penetrating flow was found to exist in a static cluster model and contribute much to the suspension of particles in our previous study. This phenomenon however needs to be clarified further since particle clusters in actual gas-solid flow have no fixed shapes and internal structures due to their dynamic evolution with time and space. In this article, a general guideline based on gradient calculation is proposed to identify particle clusters from solids concentration fields, so as to quantify gas penetrating flow through dynamic particle clusters. By EMMS-based CFD simulation and two-phase PIV measurement, the internal two-phase flow fields of dynamic particle clusters are analyzed to gain an insight into gas-solid interaction inside particle clusters. Both the simulated and experimental results are qualitatively consistent with the previous findings that gas penetrating flow significantly increases with the increase of cluster voidage and hence should betaken into account in the mathematical modeling of particle clusters in gas-solid fluidization. (C) 2016 Elsevier B.V. All rights reserved.