Weird looking train

[threaded]

It's a golf rather physics page - the first semi-credible one I found. Here's a better one.

Anyway, that isn't the reason for this trains shape, which is more to do with the Coanda effect.

[TimberWolf]

I've just run a few quick numbers and it turns out the biggest losses are getting up to speed, for trains that stop fairly often. And rolling resistance is almost double aerodynamic drag.

Based on: 50 tonnes / carriage * 8 carriages, steel wheel on steel track rolling co-efficient: 0.002, frontal area: 5m^2 (probably an underestimate in hindsight), crap drag co-efficient of 1, 160 km/h.

Gives:-

• Rolling resistance: 8000N
• Aero drag: 5000N
• Kinetic energy at top speed: 4*10^8 J (equating to the energy the latter two forces would expend travelling 30 km)

[threaded]

I've just run a few quick numbers and it turns out the biggest losses are getting up to speed, for trains that stop fairly often. And rolling resistance is almost double aerodynamic drag.

Based on: 50 tonnes / carriage * 8 carriages, steel wheel on steel track rolling co-efficient: 0.002, frontal area: 5m^2 (probably an underestimate in hindsight), crap drag co-efficient of 1, 160 km/h.

Gives:-

• Rolling resistance: 8000N
• Aero drag: 5000N
• Kinetic energy at top speed: 4*10^8 J (equating to the energy the latter two forces would expend travelling 30 km)

Closer is to consider the running resistance, which is usually approximated by a quadratic called the Davis Formula.

HTH

[TimberWolf]

Closer is to consider the running resistance, which is usually approximated by a quadratic called the Davis Formula.

HTH

"Wetted area" (skin friction) probably dominates over frontal area too, for a long train. For exactness, it's probably easier to build a train and measure the real thing.

[threaded]

"Wetted area" (skin friction) probably dominates over frontal area too, for a long train. For exactness, it's probably easier to build a train and measure the real thing.

True, as far as it goes, for a long train travelling at high speed, in a straight line, in the open.

Once you understand what is happening you can build really quite good simulations. Problem is that most people don't quite know what is going on, and don't know the software is available. That goes for 'experts' too: Audi made that mistake with the TT, but they bought a copy, eventually.

The train in question isn't that long, travels at a speed where side winds are important to consider, also it travels through tunnels a lot, and has to take bends. So most of the knowledge learned from high speed trains doesn't apply.

For example, a pointy nose on that kind of train increases rolling resistance...

[Churchill]

True, as far as it goes, for a long train travelling at high speed, in a straight line, in the open.

Once you understand what is happening you can build really quite good simulations. Problem is that most people don't quite know what is going on, and don't know the software is available. That goes for 'experts' too: Audi made that mistake with the TT, but they bought a copy, eventually.

The train in question isn't that long, travels at a speed where side winds are important to consider, also it travels through tunnels a lot, and has to take bends. So most of the knowledge learned from high speed trains doesn't apply.

For example, a pointy nose on that kind of train increases rolling resistance...

Which is why they have the bulbous surround at the "front/rear" so that when units like this are coupled the gap between the units is reduced. Cuts down on noise and buffetting.

[TimberWolf]

True, as far as it goes, for a long train travelling at high speed, in a straight line, in the open.

Once you understand what is happening you can build really quite good simulations. Problem is that most people don't quite know what is going on, and don't know the software is available. That goes for 'experts' too: Audi made that mistake with the TT, but they bought a copy, eventually.

The train in question isn't that long, travels at a speed where side winds are important to consider, also it travels through tunnels a lot, and has to take bends. So most of the knowledge learned from high speed trains doesn't apply.

For example, a pointy nose on that kind of train increases rolling resistance...

That's a good start, but then you have to go to a wind tunnel to get the right answers. And even then they may not be.

Perhaps one day computers will have the power to simulate using Newtons laws, rather than macroscopic approximations.

[gricerboy]

OK I take the bait

I know this thread has been set up to elicit some kind of response from me; now, what do you want me to say? I really coiuld go on all day here.

[Mich the Tester]

I know this thread has been set up to elicit some kind of response from me; now, what do you want me to say? I really coiuld go on all day here.

It wasn't set up to elicit a response from you, but to request an explanation of the train's aerodynamic qualities.

However, feel free to enlighten us with your knowledge of railway related matters/

[Drewster]

It wasn't set up to elicit a response from you, but to request an explanation of the train's aerodynamic qualities.

However, feel free to enlighten us with your knowledge of railway related matters/

He hasn't googled it yet.........