The premixed flame propagation in a closed duct with a 90 degrees bend is studied using high-speed schlieren photography and numerical simulation. The investigation provides basic understanding of the influence of the bend on the premixed flame propagation. The flame undergoes four stages in the propagation. The outer flame skirt influences significantly the flame dynamics. The flame surface area reaches its minimum value after the full formation of tulip flame. The flame dynamics observed in the experiment is well reproduced by the numerical simulation. The flame behavior at the later stage is in close connection with the hydrodynamics of the combustion-generated flow. The numerical simulation indicates that a single vortex is generated near the flame tip in the burnt gas just before the formation of flame indentation. The vortex remains in the vicinity of the flame tip and changes the flow field around the flame front. As a consequence, the effects of the circulating flow create the conditions required for the formation of a tulip flame. (C) 2013 Elsevier Ltd. All rights reserved.