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Old 02-11-2011, 10:35 AM   #17 (permalink)
Piwoslaw
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Piechna's book has a short chapter on train aerodynamics, so I though I'd add that info to this discussion.

Here is a simple comparison of how nose and tail cones effect the drag coefficient Cx.
This data comes from Wysocki's testing of train models ([1]), in this case a 250 km/h train.

Next, a more detailed comparison of different train sets.
Example a is from Wysocki ([1]), b and c are from Gackenholz ([2]).

Here is the effect of each element of a loco (Wysocki [1]).

And the same for wagons/cars (Wysocki [1]).
Notice the effect of covering the underside.

All models were done with Reynolds number above the critical value (which most researchers assume to be greater than 10^5), based on the height of the train. Gackenholz ([2]) used Re > 10^5, Neppert and Sanderson ([3]) used Re = 4x10^5, while Wysocki ([1]) noticed that the drag coefficient does not change above Re = 5x10^5.

Sources:
[1] Wysocki Z., Badania aerodynamiczne zespołu trakcyjnego 4WE, Spr. Inst. Lot. nr 29/BA/76, 1976.

[2] Gackenholz L., Ergebnisse neuerer Untersuchungen zum Luftwiderstand von Fahrzeugen in Zugverband, Elektrische Bachnen, Heft 12/42, 1971.

[3] Neppert H., Sanderson R., Untersuchen zur Schnellbahn-Aerodynamik, Z. Flugwiss 22 (1974), p.347.
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