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Study of the transit of a high speed train
The passing of a train at high velocity underneath the cover can cause two possible
problems. The first problem is the occurrence of a positive differential pressure
underneath the cover. The effect of this pressure on the eardrums of commuters can
be experienced as unpleasant or even painful. The pressure differential also implies
an added stress on certain parts of the cover’s structure. The second problem is the
occurrence of airflows underneath the cover. These imply air velocities which need
to be examined with respect to the safety of the passengers on the platforms.
Positive pressure differential underneath the cover (rough estimate)
The passing of a train underneath the cover was simulated as the passing of a train
through a tunnel. The train pushes a certain volume of air forward, causing a pressure
wave which spreads throughout the space under the cover. The maximum pressure
increase is mainly determined by the speed of the train and by the ratio between the
frontal surface area of the train and the frontal surface area of the cover.
For a frontal area of a train of 9.5 m², a total cross-section of the cover measuring
480 m², and a train velocity of 160 km/h, the maximum pressure increase under the
cover amounts to an average of 60 Pa over the entire surface area of the platform.
However, local higher pressure values are possible. This is the case in the direct
vicinity of the train, between the roof of the train and the cover itself. The cross-
section reduction is the most pronounced in that very area during a train transit.
Local measures in pressure increases are as high as 1,000 Pa on the underside of
the cover.
In short, an average, evenly distributed pressure increase of 60 Pa, and local,
fluctuating pressure increases up to 1000 Pa have to be taken into account.
Airflows
Distance observer - train velocity of the airfow
0.4 m 11.3 m/s
0.8 m 6.5 m/s
1.6 m 2.8 m/s
3.2 m 0/8 m/s
The passing of a train causes airflow on the platforms with a principal velocity
perpendicular to the train. The maximum air velocity is relative to the speed of
the train and the distance between the observer and the train. The table above
indicates the results for the calculation of the air velocity during a high speed train
transit at 160 km/h, considering different distances between observer and train. At
a distance of more than 1m from the passing train, the air velocity is lower than
6 m/s or 21 km/h.