地下軌道運輸系統活塞效應之模擬分析

Abstract

當前交通發達，搭乘大眾運輸可說是大家的日常，其中又以軌道運輸最為重要，因為人們較能準確掌握出發即抵達的時間；在都市擴張下，軌道運輸的發展方向已趨向地下化，然而鐵路地下化所面臨的考驗是:在狹窄的空間下，列車高速經過帶來的風場變化，是否會對人體或者軌道、車站設施造成安全上之疑慮? 當列車在地下隧道中前進時，由於列車的流體不可穿透性，會導致列車前方的空氣受到列車撞擊而有往前的動量，而這能量會隨時間不斷往下游傳遞如波的傳遞，該現象稱為活塞效應(Piston effect)。當列車靠近車站時，會推引大量空氣快速灌入月台層，導致月台門會面對較大壓力而有遭受破壞產生人員受傷的疑慮。由此，車站往往會設計釋壓井，作為活塞效應的緩解工具。 本研究採用商用CFD模擬軟體PHOENICS，有限體積法進行模擬單列列車以車速40公里/時、65公里/時、以及80公里/時，以及雙向列車以車速65公里/時通過車站時，發現月台門壓力隨車速升高；而釋壓井的存在確實大大舒緩了列車進站瞬間造成的巨大的壓力；於模擬時有無開啟重力項對於結果也有很大影響，單純加入重力項會使得釋壓井內空氣因為自身重量流入站內造成垂直的壓力梯度，進而使月台門壓力升高、釋壓井淨流入流量升高。

Nowadays, transportation system is becoming well-developed in the world, and taking public transportation can be said to be everyone''s daily life. Among them, rail transportation is the most important, because people can accurately take full control of the time of departure and arrival when they use this transportation. Under the urban expansion, there’s no more space for the construction of this kind of transportation, so the development direction of rail transportation has tended to go underground. However, the biggest challenge it faces is: when trains with some speed moving in a narrow space, will the abrupt changes in the wind field caused by the high-speed passing of trains cause safety concerns for the human body or track and any station facilities? When a train moves in an underground tunnel, due to the fluid impenetrability of the train itself, the air in front of the train will be impacted by the train and gain forward momentum, and this energy will continue to be transferred downstream like waves over time. The phenomenon is called the “Piston effect”. When a train approaches a station, a large amount of air will be pushed into the platform floor all of a sudden, causing the platform door to be exposed to greater pressure and possibly damaged accordingly, raising the risk of personal injury. Therefore, stations often design pressure relief well as a tool to mitigate the piston effect. This study uses the commercial CFD simulation software “PHOENICS” to simulate a single train passing through the station at a speed of 40 km/h, 65 km/h, and 80 km/h, and a two-way trains passing in two opposite directions through the station at a speed of 65 km/h. It is found that the platform door pressure changes with time. The pressure platform doors face rises when the speed of the train increases; and the existence of the pressure relief well does greatly relieve the huge pressure caused by the moment the train enters the station; Whether or not the gravity term is turned on during simulation also has a great impact on the results. Simply adding the gravity term will cause the air in the pressure relief well to flow into the station due to its own weight, causing a vertical pressure gradient, which will increase the platform door pressure and cause an increasing net inflow of air into the pressure relief.