According to Swedish KTH railway group, in long trains surface friction from
sides and roofs accounts for 27,0% of air resistance, the underfloor equipment
for an additional 7,5 %. Since these effects are roughly proportional to train
length (which is not true for effects from head and tail!), they play a smaller
(but still significant) role in short trains.
There is some potential for improvement by
- streamlining the outer shell
- finding surface coatings for train sides and roofs that minimise surface
friction
- optimising coach transition areas (which cause major flow separations).
ETC recommends that gaps between consecutive coaches should not exceed 250
mm.
- optimising arrangement of windows, doors and door steps
- underskirting, i.e. covering the rugged structures of the underfloor
surface by a smooth cover.
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