The Method Research On Compensation Of Maximum Gradient For Long Railway Tunnel

The current code for design of railway line provides that the the additional resistance would increase and the coefficient of viscosity would decrease, when the length of cargo and passenger railway tunnel is more then 400m. In order to prevent the trains running delay and even stoped, the sum of tunnel design gradient and equivalent gradient must not greater than the limiting gradient, and at the same time the Maximum Gradient need to be compensated. However the influencing factor of tunnel air resistance has changed in china, the calculation methods of reduction factor of tunnel gradient is unreasonable, so we need to do some research on the subject.Firstly, by using theoretical analysis, numerical computation, statistical regression and other research methods, the theory of compensation grade of tunnel and computing method were studied systematically. In this paper, a formula is derived to calculate the biggest slope of cargo and passenger railway. Experimental research and test date by domestic and foreign were obtained to derive the formula of air drag of train in the tunnel, at the same time the modern trains and engineering parameters were used to modify the formula. The air computation model of trains running in the single track tunnel was created.Secondly, the software of AutoCAD was used to build streamline and blunt-head train models. And then the models were imported the software of Gambit which belongs to the pretreatment software of the CFD. It can generate meshes and set the relevant boundary conditions, and finally the air drag of trains running in the different tunnels can be calculated by the software of Fluent. By comparing the air drag of trains running with the steady-state, the additional air drag of trains can be worked out, and at last the compensation grade of tunnel could be obtained.The data of the compensation grade of tunnel which based on the computer emulation compared with the date obtained by the numerical simulation was small. A conclusion that proves the dates which based on the numerical simulation to be safe can be obtained.