عنوان مقاله [English]
Aerodynamics of high-speed train is of interest to the world researchers in recent decades. High-speed railways shows a continuous growth over the last few years in many parts of the world, both in terms of speed of the train and the number of lines. The world record for the highest speed achieved on a conventional high-speed railway line is currently held by the modified version of Alstom's TGV, which reached close to 575 km/h on a test run. The aerodynamic forces generated at such high speeds would be very significant as they are proportional to the square of the train speed. It is not surprising that there are many problems that need to be addressed. The operation of these high-speed trains can be unsafe if certain requirements are not fulfilled. One of the aerodynamic problem, engaged to the high-speed train passage, is flying ballast. The flying ballast is the rotation or jumping of the ballast due to the produced high-speed train pressure wave. The flying ballast may damage the wheel system, the infrastructure, stations and structures close to the rail. The purpose of this research is to determine the critical velocity of aerodynamic wind for flying ballast and to introduce a strategy of risk reduction. The flow problem under train is modeled analytically as a turbulent Couette flow. The air velocity profile solution is compared with two-dimensional model using Gambit \& fluent software. Three-dimensional modeling of ballast under wind profile is done analytically and numerically (fluent) to determine the critical wind speed. Wind tunnel test is done, for the ballasts in range of 30 to 170 gr, and critical velocity is compared. The results show good agreement with the analysis and test. Finally, the ballast flying possibility factor (BFPF) is shown, and strategies to reduce risk factors and strategies to control flying ballast are introduced.