An external design for performance improvement of the transition windbreak wall between an embankment and a hill cut on a high-speed railway

Abstract The embankment and the hill cut are conventional infrastructure scenarios along the railway line in windy regions. The windbreak walls with the same height are separately installed on them to guarantee the safety of train operation. However, due to the realistic terrain, the distances of windbreak walls on the embankment and hill cut from the railway centreline are not the same, generating a windbreak wall transition and causing a sudden change of the windproof performance, which contributes to the so-called ‘yawing’ phenomenon when the train passes through the windbreak transition. The current study aims to predict the flow characteristics around the existing right-angled windbreak wall, with three preliminary designs and four local improvement designs at the transition connecting the embankment and the hill cut along the high-speed railway. The detached-eddy simulation method with the realizable k-ε turbulence model was used, while the contour lines were applied to generate the realistic terrain. The velocity distributions in the existing windbreak wall transition present a fast change from the large negative value (i.e. −0.16U on windward line (WWL) and −0.20U on leeward line (LWL)) to the positive value (i.e. 0.47U on WWL and 0.42U on LWL) within the distance of 10h. The different locations of windbreak walls on the embankment and hill cut create a rectangular discontinuous transition. The consistency of the windproof performance is destroyed at the windbreak wall transition, resulting in a sudden gust on the railway lines. A preliminary design idea coming from the hypotenuse on a right triangle was proposed to smooth the transition from the windbreak on the cut to that on the embankment. Three included angles were discussed, and the 30° scheme shows the best shielding performance, achieving about 46% reduction on the peak-to-peak value on the WWL and 32% on the LWL at the middle height of the train. However, the positive peaks are still observed. On this 30° scheme, four local improvement designs are attempted to further smooth the velocity distributions. The best design that meets three wind directions can achieve about 80% reduction of peak-to-peak values. All achievements can provide a reference for the design of windbreak walls at different transitions and improve the safety of train operation under strong winds.