Abstract: he fluent software is used to simulate and analyze the piston effect of quasi- rectangular tunnel without fire door under different speeds and different arrangement of connecting passage. The results show that: There is a positive correlation between piston effect and vehicle speed in the tunnel; When there is no fire door, a single line train passes through the connecting channel, resulting in a flow field change of less than 2 m/s in the other side of the tunnel; When two connecting channels are set, the flow velocity in the center of the connecting channel will fluctuate greatly when the train passes through, and the flow velocity on the left side is always smaller than that on the right side; Under the influence of the expansion wave at the rear of the vehicle and the connecting passage, the pressure at the front of the vehicle first decreases, then increases, and then decreases after passing through the connecting passage. 

Key words:

quasi- rectangular tunnel, connecting passage, piston effect, numerical simulation  ,