6. Calculation of the aerodynamic coefficient on trains in half-bank half-cut line sections

  • A quantitative evaluation was made of the aerodynamic coefficient of trains on half-bank half-cut sections of line
  • For winds acting at an angle of 90 degrees on intermediate carriages, it was observed that running safety was higher with cut banks of a height of 10 m or half-bank half-cut embankments of 15 m.
  • A proposal was made to use the aerodynamic coefficient as an indicator for evaluating safety in high winds on sections with half-bank half-cut embankments.

Evaluation of running safety in high winds is carried out using an aerodynamic coefficient obtained from wind-tunnel tests. There are many types of section topography along actual railway lines, however, the aerodynamic coefficient is sought for seven standard types of track-side structure. Many lines close to the coast or rivers are often on tracks flanked by a slope on one side and a bank on the other (half-bank half-cut sections), and are treated as embankments. However, on sections with high embankments on the downwind side, the lateral force acting on the train is lower than on normal embankments, which means that the aerodynamic coefficient is probably smaller.
Therefore, wind-tunnel tests were conducted to obtain the aerodynamic coefficient on a half-bank half-cut section. During the wind-tunnel tests, the angle and height of the cut slope was varied along with the distance between the cut slope and the train center (Fig.1).
Results showed that in cases where the cut slope was 10 m or 15 m, as the distance grew shorter between the side of the train and flanking cut slope, and as the angle of the slope became steeper, the lateral forces acting on the intermediate carriages of the train at 90 degrees fell between 5-100% (Fig. 2).
The outcome of these experiments shows that safety evaluation of half-bank half-cut sections can be carried out more suitably than simply applying the standard embankment evaluation method used previously.

Fig.1 Wind-tunnel experiment and parameters for tests on a (actual scale) half-bank half-cut section (Reduced scale: 1/60, Train: roof curvature radius of 5000 mm (actual scale) of a commuter train)
Fig.2 Comparison between aerodynamic coefficients on a half-bank half-cut section and a normal embankment (intermediate carriages, wind angle 90 degrees, top of cut slope and distance to slope of 20m)