Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - Fascinating free paper

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Fascinating free paper - but it's on trains, not cars

https://www.sciencedirect.com/scienc...dgcid=coauthor

What a great paper! Well written and fascinating results. Worth reading for anyone interested in vehicle aero - not just trains.

They instrumented a shipping container on a train, placing pressure taps/front and back.

Key points to look at:

- how Cd is calculated from just front and rear pressures
- how Cd varied little with speed (as expected) but varied a lot with crosswinds - see graph below
- the different pressure patterns on the container with crosswinds
- how Reynold's numbers are important, because the 'length' criterion varies with the position of the container along the train
- how boundary layer thickness is important - and again varies with position along the train

And, for anyone just interested in tech, how they instrumented (and then retrieved data from) a freight train travelling across one-third of Australia, with no researchers on board.

Variation in drag with wind:

https://ars.els-cdn.com/content/imag...1-gr13_lrg.jpg

"Access through your Institution to view subscribed content from home."

Outline and Figure thumbnails are available.

Quote:

Originally Posted by freebeard (Post 640417)

"Access through your Institution to view subscribed content from home."

Outline and Figure thumbnails are available.

Oh. I can download the whole paper.

Does this work? https://reader.elsevier.com/reader/s...23942D1DE766F5

Nope, it must be restricted for US readers. (I can see if I can get it at my college library or the university library next time I'm there).

Ok sorry about that. I just tried accessing it through an anonymous browser and it wouldn't let me in either.

So I must have gained access to the system when I was writing my book. I didn't pay any money, and I didn't do it illegally, so it might be one where if you're a researcher / author / etc they'll let you apply and then grant access.

I'm not seeing the link either.
It asks for a login.

One question I would like to ask about trains that may be covered in the article, is why that modern trains got rid of streamlining.
Sure passenger trains are still streamlined, but what about average freight trains ?

They go so far as to have exposed ladders on the sides, and look like a blunt anvil.

I have seen others explain it away as " Well they don't go very fast ", but as we all know, even at 45 mph there is a huge amount of drag.

From the paper's intro:

Diesel-powered locomotives remain one of the most favoured means
of hauling freight by trains over long distances. Reducing fuel consumption of existing freight trains by better understanding the resistances that need to be overcome has never been more relevant. One source of energy loss, the aerodynamic resistance (drag), has not had the
same research focus when compared to other vehicles, such as cars and
high speed trains. This may be in part due to an inaccurate perception
that inter-modal freight trains travel at low speeds

The paper should be available by request from here.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7153308/

This is not about trains, but I wanted to share and didn't know where to add it in the forum.

And here is another.

https://www.sciencedirect.com/scienc...67610501001611

It may have been posted already.
In fact, it may be a paper we all spoke about earlier.
( I'm trying to find more information on ducting air into a cars' wake to reduce drag )

I might just start a new thread where i dump links to papers.

Here is one on wake reduction from a blown wake https://www.sciencedirect.com/scienc...67610515000665

It is too complex for me, but I did see one chart that showed that drag was reduced by about 2 counts through air blown into the wake. (.377 - .357 Cd )

From this paper :
https://www.sciencedirect.com/scienc...42727X18310270
.Quote " Based on our previous study (Wang et al., 2017), the drag can be reduced only by using blowing or suction method at certain edges of the rear body, otherwise it would be increased "

So apparently blowing air into the wake has to be just right, or you end up increasing drag.
"

I was actually thinking about this the last few days. I was reading Road Vehicle Aerodynamics 1st ed. and there was a section (6.3, pg 115 if you have the book) about "BASE DRAG REDUCTION BY INCREASING THE WAKE PRESSURE" and it was very interesting. The main way he offered was with the exhaust gas from the engine, but for it to work well you needed a large displacement or turbo charged engine (high volumetric efficiency) to make a significant difference in terms of what is possible with this method. You also need to slow the exhaust gas down so that instead of ejecting the gas out of the wake it "pumps" it in, increasing the pressure in the wake. Also don't forget that with the exhaust it would work optimally during acceleration as it won't pump out as much gas at low throttle cruise.

I thought it was interesting regardless though.

Quote:

Originally Posted by Scibor-Rylski

Consider the total volume of air displaced by a car in motion as the product of its maximum cross-sectional area S and its speed V, i.e SV is a 'measure' value of the air flow rate. Thus the exhaust gases from a 1.6 litre car engine produce a gas flow of order of .67% of the total value of SV, the ventilating system may produce .167% and the engine cooling system about 1.2%. All these sources of air or gas can therefore produce a combined flow rate in the wake of about 2% of the total air displacement SV.

In the case of a vehicle with an engine of 5 litres capacity the exhaust gases alone can create an injection rate of about 2.1%. As the exhaust gases are ejected from the exhaust pipe at high speed a plenum chamber is required to reduce the momentum. By losing momentum the gas increases its pressure. From this plenum chamber gas or air, or a mixture of both, is ejected through a grid to ensure the correct rate of flow into the wake...

I gave it my best shot in 2014(!):

https://ecomodder.com/forum/member-f...ed-stinger.png

The Idea was the positive displacement cooling air is ducted into a vertical stack that is perforated or baloney-cut on the front face. It is surrounded by a stainless steel concave reflector that truncates the boat tail.

Instead of volumetrically replacing the wake it uses the heat energy to 'wrap around' the airflow via the Coanda effect.

IIRC the exhaust and cooling air are both 1500cfm, but the exhaust is corrosive.

I remember the image well.
Are you the artist ?

I'd answer to 'responsible party'. :)

Were it art, the boat tail would be healed into the vehicle. It was modeled in one program and rendered in another. Neither will run on my current hardware, so that represents something of a peak.

The Raspberry Pi will run Blender, but only a deprecated version, 2.79. I don't want to unlearn 2.8x or 2.92. If (and I say if) there's another round of plague money, I'd get the new Mac Mini with the machine learning chip.