Windproof performance improvement of windbreak walls on the transition connecting a realistic embankment and a hill cut along the high-speed railway

Due to the complex terrain, inevitably the transition between an embankment and a hill cut can be observed along the high-speed railway in windy region. How to design a transition windbreak wall to smooth the sudden change of the windproof performance when the windbreak walls are separately installed on the embankment and the cut has important significance. This study attempted to predict the flow characteristics around the existing right-angled windbreak wall and four different designs at the transition using a detached-eddy simulation (DES) method with the Realizable k-ε turbulence model. The realistic terrain was reconstructed from geographic contour lines. For the existing windbreak wall at the transition, the crosswind with a 90° wind angle has a dominant impact on the velocity distributions on the railway lines, contributing to large peak and peak-to-peak velocities. This ascribes to the right-angled discontinuous transition between two windbreak walls which are located at different heights and distances from the center of the track top. Including an internal section of windbreak walls with an included angle and removing the existing transition, a larger reduction of velocity peaks those are less than 0.2 U is obtained. Additionally, installing an external section of windbreak walls with an included angle has benefit to reduce the velocity peaks on the railway lines, especially after increasing the height of the windbreak wall at the hill cut root and linking the tops of windbreak walls on the embankment-transition and cut-transition. The improved design Case4 has been put into practical application.