Railroad Train Aerodynamics
 

Hello all.Cd got a thread going about freight-train streamlining and I said I'd dig out what I had from Hoerner and post it.Since that thread got off on some tangents,I thought I'd begin a new thread.

The following material is from AERODYNAMIC DRAG,by Sighard F.Hoerner,1951.The material does not pertain specifically to freight trains and probably due to considerations already mentioned by BicycleBob,ConnClark,BigDave,MetroMpg,and others.We may derive some insight into the potential gains for freight trains,if only for academic reasons,as the practicality of ideally streamlined trains rubs up against some unique hurdles when considering the myriad forms of freight cars and there possible combinations within a "train."

It appears that the "state-of-the-art" for railroad train aerodynamics was basically in the bag by 1932.Researchers,Tietjens and Ripley had developed a self-powered railcar design with Cd 0.08 by modifying an inter-urban trolley with an inverted and reversed boat hull body,with full boat-tail.You can see this form operating today in Japan,between Sendai and Kitakami with East Japan Railway's Shinkansen 'bullet train'.This would compare to the trolley's original Cd 0.50,and Cd 0.80 for a San Fransisco Streetcar.

In 1939,when GM's Diesel/electric locomotive debuted,standard steam locomotives with tender demonstrated drag coefficients in the range of 0.98-0.37.A New York Central Railway train with single passenger "tail car" was Cd 0.97,with 2-cars Cd 1.17,and with 3-cars Cd 1.27.

A standard "Pullman" or "Harriman" passenger car (within the train ) had drag coefficients on the order of Cd 0.18 ( measured by actual draw-bar tests ).The Cd of additional cars was basically constant,all within a 3-car NASCAR draft,with exception of tail car,which saw the base-drag.

By streamlining to the "ideal" shape,the drag of the cars could be reduced to Cd 0.05.

At 100-mph,a 800,000-pound,100-square-foot frontal area,6-coach passenger train could be streamlined to reduce it's power load from 2,100 -horsepower,to 1,012 -horsepower,over 50 %.

At 60 mph,a typical standard train would see equal mechanical resistance and aerodynamic loading.

The "Total" aerodynamic load is a combination of locomotive frontal drag,skin-friction of all the cars,and base-drag of the tail car,and centrifugal pumping losses at each exposed wheel.

Flat-out,at 100-mph,the standard train would see 5,900-lbs of air resistance,where the ideal streamliner's would be cit to 1,300-lbs.

Since trains are "long" in comparison to automobiles,skin-friction plays a more significant role.Each car's wetted-area is approximately 15X it's frontal area.A 6-car train would have on the order of 100X it's frontal area in wetted surface.

Given that today's mile-long freight-trains could be configured with any mix of box-cars,flat-cars,auto-haulers,tank-cars,hopper-cars,double-stacked container-box cars,they pose a veritable torture-chamber to the air.In their defense however,consider the following from a CAR and DRIVER "road-test" of a GM Electro-Motive Division,SD-60 Locomotive,from September,1990.

The 195-ton locomotive pulls a 12,000-ton train,at 70-mph,consuming 187-gallons per hour.

12,195-tons,times 70 miles per hour,equals 853,650-ton-miles per hour,divided by 187-gallons of Diesel per hour,yields, 4,565-ton/miles/gallon.And that's with a hodge-podge of railcars behind it.

I compared this with a CAR and DRIVER "road test" of a 633-foot,roll-on/roll-off ( Ro-Ro ) ship.The 17,500-ton GVW ship,carrying 6,400 automobiles,at 20-mph,consumes 60-"TONS" of bunker fuel a day.

At 20 mph and 24-hours/day,the Ro-Ro covers 480 miles a day.At 60-tons a day,that's 120,000-lbs of fuel.Dividing by 24-hours,that's 5,000-lbs per hour.Dividing by 6-lbs/gallon,yields 833 gallons per hour.

So,17,500-tons,times 20 miles per hour equals 350,000-ton-miles/hour,divided by 833-gallons,yields 420-ton-miles per gallon.

These are only gross figures and without tares for the railroad and ship it's hard to make a comparison as to energy spent per net cargo mile.I'm hoping some of you will jump in and help fill in the blanks.

As I mentioned in the opening,while there may be significant theoretical room for aero improvement in freight-trains,the practical barriers to implementation may far over-shadow their implementation.A real can of worms!

One closing remark,and it has to do with the Ro-Ro ships.In the article,the Wallerius Line spokesperson mentioned that ocean-going shippers are actually looking into submarines for the future in shipping.Evidently,the rough seas and gale-force wind loading on hulls makes underwater "weather" look very attractive and potentially more profitable.

MetroMPG/Hucho-boundary-layer/ tails
 

I forgot this and had meant to include it.Darin had posted the other day a citing by Hucho regarding the back of trains.In Hoerner's book,he reports that the actual boundary layer thickness around trains,at the time of publication,could not be accurately deduced from formulas and would have to be established empirically from observation.

Trains were exhibiting boundary layers of areas greater than 10 X the base area of the tail car.

And as Darin has reported,with the tail of the train embedded within all this noisy air,the aftbody shape might not have the significance one might presume.

What strikes me,is that in 2005,the Shinkansen began tests of two experimental 52-foot-long aerodynamic nosecones ( tails ),and by 2006,were running the form essentially established by Jaray/Klemperer in 1922.It also looks suspiciously like the inflatable/extensible bus boat-tail depicted in Hucho's text.What's old is new again.

For anyone coming late to the discussion, the other thread Phil mentioned is
http://ecomodder.com/forum/showthrea...ined-7378.html

But on the other hand, sails are making a comeback: SkySails - Home en

... Fixed ...




Sorry, couldn't resist... :p

skysails
 

Man,that put a smile on my face! A friend had just done a blog at EV World on a hybrid ship from around 1830,which combined steam-power and sails and I'd been seeing sails in my mind.---------------------- Good for those folks.Hope their profit curve looks just like the tether leading up to the sail.Thanks!

I looked at the Sky-Sail rig and wondered that with computer control you couldn't put two or more of these kites up and further reduce fuel consumption.

On old sailing ships, what was the mast but a means of holding the sails in a fixed position relative to the ship? This does it with automatic kite control.

Could you see maybe four of these pulling a 2,500 ton ship along with the engine shut down?

Ah ha. I've read more than a couple of quotes in Hucho that seem to be generalizations, and his train comment may be another. Maybe he's missing a few qualifications there.

It makes sense to me that a relatively "short", high speed passenger train with uniform and streamlined coaches is a different animal than a mile long, jumbled up freight train, in terms of boundary layer thickness at the end car.

Efforts to "boat tail" the passenger train are worthwhile obviously.

Railroad
 

Can you imagine an extremely light,light rail,with Cd0.08,and a fraction of the rolling resistance of a rubber tire on pavement?------------------------------ I could erect a " Roller-Coaster" that used wind and solar power to raise the empty car to the top of the incline.Have a bunch of folks take an elevator up to fill it.Then coast,from downtown Dallas,40-miles out to Denton,on gravity power alone at over 100-mph!--------------------------------------------------------------- People pay alot of money to have as much fun at Six-Flags Over Texas over in Arlington!------------------------------------------------------------- Mass-transit anyone?

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