PISTON EFFECT ANALYSIS FOR THE METRO VENTILATION
The purpose of the present work is to assess the influence of the piston effect in the subway tunnels depending on the speed of train, geometry of tunnel and train, types of air flows and other variable characteristics. The article deals theoretical analysis of the piston effect and results of numerical modeling in the subway tunnels. Tables and graphs of changes in the generated air flows are presented, depending on the speed of the train and the degree of filling of the tunnel. It is noted that of the piston effect is characterized by two phases. In the first phase, the piston effect and changing processes of physical fields are a non-stationary, and in the second phase the processes are stabilized. For the air flow ahead of the train as well as backflow through annular space and direct air flow after the train, it is necessary to consider the influence of these phases. The speed of the circulation flow created by the piston effect, in accordance with the tunnel filling factor, is characterized by a linear relation, and the extent rate of its growth is directly proportional to the speed of the train. Maximum value of the air consumption carried out by the piston effect for the train's speed of the 40-45 km/h range, does not exceed 90-100 m3/s, in the Tbilisi metro conditions that corresponded to the speed of the stationary phase of moving, when the tunnel filling coefficient = 0.35.
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