Large Eddy Simulation of the flow around a typical container wagon in a freight train
The sum of the resistive forces acting on trains in the direction of travel is usually expressed as
F = A + B x V + C x V^2 (1)
Here, it is assumed that the train does not accelerate and that it travels on flat ground and that the railway is straight. Otherwise, terms for the forces needed to overcome the resistance of acceleration, the gravitational force and mechanical curving resistance have to be included in Eq. 1. The term A on the right hand side contains mechanical resistances that are constant with respect to the speed of train, V but dependent on the mass of the train. The second term contains resistances that are considered to be linearly proportional to speed. The last term contains the aerodynamic resistance of the train which is proportional to the square of speed. A freight train normally consists of a large amount of wagons of different sizes, shapes and purposes. For a freight train the coefficient C in Eq. 1 is the sum of the contribution to the aerodynamic drag from the locomotive and all wagons in the train. The size of the contribution to C from each wagon depends on the position of the wagon in the train
Shown in Fig. 1 is the drag coefficient of a closed top gondola-type of freight wagon depending on the position in the train. Results are shown for 0, 5 and 10 degrees of yaw angle. It is seen that after the initial 3-4 wagons, the drag coefficient will reach some steady value that is some 20-50% less than the drag coefficient of the second wagon. The contribution to the total drag of the entire train from the locomotive will in turn be higher than the drag of the second wagon due to the contribution from the stagnation pressure of the air on the front of the locomotive. The majority of all wagons in a freight train will experience an aerodynamic drag force slightly lower than that experienced by the first wagon in the train.
Aim of the thesis
The aim is to accurately simulate the flow around 3-4 four container wagons in order get “typical” flow conditions around the middle wagon. The flow around that wagon will be analyzed and the sources of aerodynamic drag should be localized. If the outcome from the simulations is well and the student makes progress quickly, some means of reducing the aerodynamic drag of the wagon will be investigated in the project. Computational grids around the wagons will be constructed by the student by using the commercial grid generator software Ansys ICEM CFD. The simulations will be carried out on large scale computers clusters with the CFD software AVL Fire. The grids are expected to reach +20 million grid points with high geometrical details. Thus, it will be required by the student to acquire high skill level in grid generation using ICEM CFD. The analysis of the flow will be carried out with the EnSight visualization package.
This project is suitable for one highly motivated Master student with interest in vehicle aerodynamics. This is an excellent opportunity to learn the necessary softwares used in the CFD process as well as getting state-of-the-art knowledge about applied Large Eddy Simulations in vehicle aerodynamics. The extent of the project is 30 credit points. Working environment will be provided at campus Johanneberg at the division of Fluid Dynamics. The interested student should send an e-mail to supervisor with an extract of his/her passed courses.
 S. Watkins, J. Saunders, H. Kumar. “Aerodynamic drag reduction of goods trains”. Journal of Wind Engineering and Industrial Aerodynamics, 40: 147 – 178, 1992.
Uppdaterad: 15 februari 2012
Ansvarig för sidan: Christian Johansson