Time Variant Characteristics of Piston Wind for Billboards Affiliated with Subway Tunnels

In order to predict the time-variant characteristics of a piston wind for billboards in subway tunnels, a simulation based on computational fluid dynamics was employed to solve the three-dimensional unsteady flow problem. User-defined functions were used to define the movement manipulating the train and the dynamic mesh, thereby leading to the establishment of a more accurate simulation method for the piston wind. The rationality of the method was verified according to previously conducted experiments and simulations by Kim. A full-scale tunnel model was then set up based on a real tunnel cross-section. Different train speeds were taken into account to analyse the flow field changes caused by train movements, thus focusing on the changes of the static pressure on the billboard surfaces in subway tunnels. The results show that speed increases cause the static pressure on the billboards to increase significantly, thus changing from positive to negative when the train passes by. The static pressure amplitudes exceed 500 Pa for train speeds of 80 km/h and 1 kPa for some subways at an operating speed of 120 km/h.