- A two-fluid model was used to determine the influence of the gas phase on granular flow interaction with obstacles. The governing equations of two-dimensional, two-phase flow were solved numerically using a finite-volume-based numerical code. The numerical results are qualitatively compared to experimental observations from various sources, and good agreement is found. Several cases were tested in order to examine the role of the velocities of both phases, solid volume fraction, particle diameter, and gravity. The results show that under certain conditions, particularly for dilute flows, a bow granular shock wave clearly forms in the front of the obstacle. Alternatively, for dense flows, granular shock waves were not observed. Based on the present observations, it appears that the formation and the shape of the bow granular shock wave are influenced by the interaction between the solid and gas phases and the gravity force. The results indicate that the common assumptions of neglecting both the gravity and the influence of the gas phase on the granular flow, may be appropriate only in the vicinity of the obstacle, where granular creeping flow takes place.