The hydrodynamics of a jet-driven swirling flow has a dramatic influence on the separation performance of a spray granulation tower. To understand the macro-instabilities of the flow patterns, this work performs a detailed study on the gas flow field in a spray granulation tower with an array of nozzles. The experimental results attained by a phase Doppler particle analyzer (PDPA) indicate that the flow field is in a fully turbulent state and that a low-frequency oscillation exists in the spray granulation tower. The velocity profiles and frequency distributions obtained using the full-scaled grid system and the Reynolds stress model are in good agreement with experimental data. Based on the observed flow field, a general flow pattern is summarized. Both the experimental and numerical results indicate that a quasi-periodic unsteady velocity flow is observed in the spray granulation tower. Compared with the original spray granulation tower, it is beneficial for reducing the flow oscillation and velocity fluctuation when the baffle is added. The flow stability criterion proposed in this study can characterize the flow state in the spray granulation tower. (C) 2016 Elsevier B.V. All rights reserved.