A validated numerical investigation of the effects of high blockage ratio and train and tunnel length upon underground railway aerodynamics

Abstract

In order to ensure the safety and comfort of passengers and staff, an underground railway requires an extensive ventilation and cooling system. One mechanism for underground railway ventilation is the movement of air induced by trains, termed the 'piston effect'. This study investigated the effect of altering the blockage ratio of an underground train upon the ventilating air flows driven by a train. First a computational model was developed and validated with experimental data from literature. This model was scaled to represent an operational underground railway with high blockage ratio and the blockage ratio varied to evaluate the effects upon ventilation. The results of this study show that ventilating air flows can be increased significantly during periods of constant train motion and acceleration, by factors of 1.4 and 2 respectively, but that the train drag will increase at the same rate. During deceleration negligible increases in ventilation flows are found but drag increases by a factor of 4.

Study on the Influence of Bolt Anchored Catenary on Tunnel Lining Under the Aerodynamic Load

“…(2) The numerical simulation shows that the force imposed on the lining structures by affiliated facilities under the aerodynamic loads stress is mainly on Y direction, and the stress of the lining structure caused by the passing of the train is a cycle of tension, compression and tension. (3) When the train speed is 400 km/h, the stress of X direction is 88215 Pa, while Y-direction stress is 348901 Pa. with no consideration of aerodynamic load when designing the lining structures is obviously unreasonable. (4) The maximum normal stress of tunnel lining with train speed according to the power law, and maximum normal stress with train speed according to quadratic function relation; (5) Considering about the safety of the actual operation of the train and the complexity of the treatment of the tunnel structure disease, this paper has some reference values for the design of the lining structures of the high railway tunnels.…”

“…At this time, the tunnel lining structure is subjected to the maximum horizontal force to the right and maximum pulling force under the action of aerodynamic load; (2) When t = 6.735s, the aerodynamic load in the tunnel reaches the maximum negative stress (AIR-STRESS = -2136 Pa). At this time, the tunnel lining structure is subjected to the maximum horizontal force to the left and maximum upward pressure under the action of aerodynamic load; (3) As shown in Figures 5 and 6, the stress of the lining structure caused by the passing of the train is a cycle of tension, compression and tension; (4) The X and Y directional stresses of the tunnel lining reach 37 times and 146 times of the aerodynamic load, respectively.…”

“…With the increase of the train speed, the aerodynamic effect of the tunnel is more and more obvious, and out of the consideration of the comfort of high-speed railway train, the tunnel construction and the economy of the vehicle manufacturing, many experts in domestic and overseas have conducted a series of numerical simulations, model tests and field experiments on tunnel aerodynamics. For example: Miyachi T and Ozawa S [1], Cross D and Hughes B [2], Luo Jianjun [3][4] Ma Weibin et al [5][6][7] improved the computational theory of tunnel aerodynamics further through the numerical simulation study.…”

Enhancing the piston effect in underground railway tunnels

“…Since the train is confined by the tunnel walls, a pressure gradient is generated along the train and air is pushed ahead of the train and sucked from behind, thus generating an air flow. The main factors which influence the magnitude of the piston effect are the blockage ratio (defined as the ratio of the train cross-sectional area to the tunnel cross-sectional area) and the train speed, length and nose shape (Cross et al, 2015;Baron et al, 2001). The magnitude of such air flows are significant and in a newly designed underground system in a temperate climate can be sufficient for ventilation during normal operations (Bennett, 2004).…”

“…The effect of the aerofoil is to increase the aerodynamic resistance of the train. As the air flow patterns around the train are changed, the volume of air displaced by the train will increase (Cross et al, 2015;Baron et al, 2006). Positioning the aerofoil at different angles allows the air flow patterns to be varied and therefore the volume of air displaced.…”