Railroad Train Aerodynamics

[aerohead]

Originally Posted by Big Dave

The coefficient of friction for steel wheels to dry steel rails is the same as rubber tires on polished glare ice.

Now the pop-out air-brakes on the Shinkansen are making more sense than ever.Guess we'll never see NHRA Top-Fuel locomotives! Funny Trains?

[wyatt]

Originally Posted by Big Dave

The coefficient of friction for steel wheels to dry steel rails is the same as rubber tires on polished glare ice.

According to Wikipedia, railroad steel wheel on steel rail has a Crr from 0.0002 to 0.0010, compare that to ordinary car tires on concrete between 0.010 and 0.015. During coast down testing, I have found my car tires to be around 0.012.

I have also found quite a bit of good information in Mark's Standard Handbook for Mechanical Engineers, Seventh Edition. I don't have time to post now on that, but I will try to post up the "summary" section which is most relevant.

[aerohead]

Originally Posted by wyatt

According to Wikipedia, railroad steel wheel on steel rail has a Crr from 0.0002 to 0.0010, compare that to ordinary car tires on concrete between 0.010 and 0.015. During coast down testing, I have found my car tires to be around 0.012.

I have also found quite a bit of good information in Mark's Standard Handbook for Mechanical Engineers, Seventh Edition. I don't have time to post now on that, but I will try to post up the "summary" section which is most relevant.

In the April 4,1994 AUTOWEEK,Page 56,Michael G.H.Scott wrote the remark," 200 times the weight can be moved on steel wheels over steel rails with a given horsepower than on pneumatic tires over a paved road."

[Bicycle Bob]

Even on glare ice, rubber tires loose energy to sidewall flexing. I'd like to see some real data on this, though. I was surprised to see that RR goes up on wet roads, even though the coefficient of friction goes down. Any moisture is bad, not just puddles.

[wyatt]

As Promised!
First some wind resistance data on trains, automobiles and ships

Now, the effect of yaw wind on trains and wind resistance on various bodies

What you should take away from this is that the streamlined train has roughly half the Cd of the non-streamlined train. Also, when there is a yaw wind involved, the longitudinal force on the non-streamlined train nearly doubles, where the streamlined train is almost unaffected.
In response to the 200x question, I used the Aerodynamic and rolling resistance calculator. I simply changed the mass and the Crr.
Run 1. Crr=.0002 Mass=200000kg
60mph - 37.5 hp
Run 2. Crr=.008 Mass=1000kg
60mph - 26.25 hp
So yes, that is really close, especially if the semi doesn't have that good of a Crr!
Run 3. Crr-0.015 Mass = 1000kg
60mph - 28.75 hp
Ship Data that may be interesting...
Ship speed = 10 knots; air resistance = 2.5% overall resistance
Ship speed = 10 knots; 20 knot headwind, air resistance = 22.5% overall resistance
similarly, small side winds may cause appreciable increases in resistance of bodies such as ships and railroad trains.
Source: Mark's Standard Handbook for Mechanical Engineers, 7th Edition, 1967.

[jamesqf]

Originally Posted by Bicycle Bob

I was surprised to see that RR goes up on wet roads, even though the coefficient of friction goes down. Any moisture is bad, not just puddles.

Think about it, though. The increase from wet roads isn't really a change in the rolling resistance of the tire, it's because energy is used to push the water out of the way. You'd get the same (or similar, this is just back-of-the-envelope) increase if you had a non-rotating tire sliding on a perfectly frictionless surface.

[Piwoslaw]

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.

[Big Dave]

Back in the late 1940s and into the 1950s Electro-Motive Division of GM – the pioneer in diesel-electric locomotives – built two different versions on the same platform. They built the streamlined F7 and E8/E9 locomotives and the GP7 locomotives built for easy servicing.

Check the links for pix.

Chicago Milwaukee St Paul & Pacific EMD F7 Diesels

The EMD GP7 Series

EMD E8 - Wikipedia, the free encyclopedia

EMD E9 - Wikipedia, the free encyclopedia

The F7 (freight) and E8/E9 (passenger) locomotives were called “covered wagons.” They were a bear to work on because of the bodywork. The GP series locomotives were very easy to work on. You could open a single dorr and change a power assembly (on EMD engines you replace entire cylinder assemblies – liner, head, conn rod and the valve gear – all in a single unit. You sent a bad power assembly off to the back shop for repair and tossed a replacement power assembly into the locomotive and got it back out on the road making money).

In twenty years of model competition the sleek E and F models were found to have no measureable aerodynamic advantage over the boxy GP units, and the ease of maintenance made the GP style win out. Today, something that looks a lot like a GP7 dominates US railroads.

File:CSX209inNNVA.jpg - Wikipedia, the free encyclopedia

Interestingly, this last pic (a GE AC4400CW) was taken at the CSX Huntington Locomotive Shop, where I worked back in the day.

The short nose evolved over the years almost back into a shape kinda like the F7. After the GP7 and GP9 which had full-height short ends, most locomotives grew a lower short end for better crew visibility. GP18s, GP20s, GP24s, GP30s, GP35s, GP38/39/40/40-2 and GP50 locomotives retained the walkways on the short nose like the GP7 had but starting with GP60s they “filled in” the walkway and put a nose door to allow access to the front. The “filled in” nose allowed bigger sand hoppers on the short end. The GE competitors followed suit with EMD on exterior sheet metal. Those bodes are not sheet metal but rather 7 gauge plate.

If you look down on a train from altitude they resemble a spear moving along the ground. A train in the US is commonly a mile and a half long, so the frontal area doesn’t affect the train much, considering that train weighs over 10,000 short tons.

Probably the easiest thing the US could do to reduce oil usage would be to find a way to electrify freight railroad mainlines. There are only about 10,000 miles of mainline left, but they haul a staggering amount of freight over those mainlines. Electrification would allow the US to use plentiful coal or nuclear power to move stuff.

[redneck]

Probably the easiest thing the US could do to reduce oil usage would be to find a way to electrify freight railroad mainlines. There are only about 10,000 miles of mainline left, but they haul a staggering amount of freight over those mainlines. Electrification would allow the US to use plentiful coal or nuclear power to move stuff.

The easiest thing that could be done to reduce oil usage on those mainlines would be to revert to superheated steam engines that use that plentiful coal more efficiently.

With advances in modern technology, superheated steam engines could provide this with less cost in infrastructure compared to electrification.
(I believe nuclear power plants are fairly expensive these days)

Besides, who doesn't love the sound of a steam engine chugging along and the personal touch of the engineer on its whistle.

I know I do...

>

[Big Dave]

The South African, back in apartheid days, used condensing, superheated steam locomotives on their Cape Town to Johannesberg routes.

They were about 9-10% thermally efficient. Diesel electrics are routinely 30-35% efficient over the duty cycle.

Can you imagine the EPA tolerating steam locomotives these days?