Braking distance when coming into a station

[chloebrown]

Hi, I'm an engineering student doing a second year design project.

The project is to use track-side wind turbines to capture the wind energy created by trains to make electricity. Although the idea isn't very feasible, we still have to carry on with it. (Note, we are not constructing anything!) The most suitable place to put the turbine would be next to the track at a point approaching the station where the train begins to apply the brakes. (The turbine would create a small amount of drag on the train, slowing the train, so it would be most useful when the train is already braking.)

I know trains don't approach stations at full speed, so do any train drivers have a rough idea of the distance? I know it depends on different trains, speed and the condition of the track, but if anyone has a range it would be very helpful!

Thanks!

 

[rodders133]

It really is so dependant like you say on certain factors, like class of train, railhead conditions etc.
A bit of advice though. Do some thorough research before deciding on a station. Make sure it has a long platform, there are no signals that would regurlarly check down trains stopping there and where possible, not in low adhesion areas.
These will be the stations the drivers will start braking later at, hence hitting your turbines faster creating more wind.

 

[GB]

I don't see why lineside turbines would cause drag to trains and even if they did, I don't suppose it would be so much so it would affect a trains performance in any way. Therefore would it not be better to place them in areas of the highest line speeds?

 

[chloebrown]

I have tried to calculate the drag but without much success, it just seemed a bit too good to be true - you can't get energy for nothing! The turbines we're designing are 3 metres tall and 1 metre in diameter like this:
http://www.tangarie.com/products/gale_vertical_axis_wind_turbine.php
I just thought they would get in the way of the air flow created by the train, impeding it's forward motion.
If you still think the drag is minimal, then yes the best place to put them would be a naturally windy place where the train also travels at it's highest speed.

 

[The Barlow Boy]

I have tried to calculate the drag but without much success, it just seemed a bit too good to be true - you can't get energy for nothing! The turbines we're designing are 3 metres tall and 1 metre in diameter like this:
http://www.tangarie.com/products/gale_vertical_axis_wind_turbine.php
I just thought they would get in the way of the air flow created by the train, impeding it's forward motion.
If you still think the drag is minimal, then yes the best place to put them would be a naturally windy place where the train also travels at it's highest speed.

And as my old grandad used to say, "if it sounds too good to be true then it is".

 

[DaveNewcastle]

I suggest you study the aerodynamics of railway tunnel mouths. The air pressure wave from the front of a train entering the tunnel mouth is a cause of weakening in the structure, and the force and profiles have been evaluated quite carefully.

As for the original suggestion, I assume that the economics of maintaining, operating and interfacing the turbines with the power network are expected to be covered by the retail value of the power generated, even during the brief few minutes a day in which a train passes. Seems unlikely to me.
As likely as . . . . .
you'll all be interested to know that the sun will rise earlier tomorrow morning because I've just thrown a pen across the room, in a westerly direction, the force of my throw adding a little more impetus to the eastwards rotation of the planet round its axis.

 

[wessex]

What about the underground, trains create a constant source of airflow.

 

[andyfrommk]

I have thought about vertical wind turbines and the railways as well, except I thought of having them in between the fastlines (see attached image)

Red: turbine blades
Blue: flywheel
Green: Alternator

DaveNewcastle: The flywheel would store kinetic energy and would transfer it to the alternator via a clutch to level out the energy gained from the trains also to not over-rev the alternator when two trains pass each other at the turbine.

Chloe: The drag caused by the turbine to the train would surely be negligable? no more drag than a platform full of passengers standing at the platform edge, you can hear the announcements now
"please stand back from the platform edge the following train does not want to be slowed down by you lot"

Network rail already use lineside turbines to power equipment( not sure what equipment, somebody more knowledgable will probably fill that info in).

 

[pendolino]

Network rail already use lineside turbines to power equipment( not sure what equipment, somebody more knowledgable will probably fill that info in).

NR use Rutland Wind Chargers and/or photovoltaic panels for traction gel applicators/lubricators

 

[chloebrown]

Ok, we've finished our project and I am assuming there is a small amount of drag (no idea how small). We are doing a presentation tomorrow and would like to have a rough idea of when a train begins to brake. 2 or 3 miles sound reasonable? (I'm pretty sure 125mph trains slow to 0mph with emergency brakes in 1.5 miles... I think!)

Any ideas would be appreciated!

 

[TDK]

Ok, we've finished our project and I am assuming there is a small amount of drag (no idea how small). We are doing a presentation tomorrow and would like to have a rough idea of when a train begins to brake. 2 or 3 miles sound reasonable? (I'm pretty sure 125mph trains slow to 0mph with emergency brakes in 1.5 miles... I think!)

Any ideas would be appreciated!

It all depends on line speed and gradient, you cannot put a figure on it but lets say the line speed is 100mph you would atrat applying the brakes about a mile and a half from the atation to get a smooth stop, this is only a rough guide as the gradients can double or half the stopping distance of a train. To produce the most engergy the best place to place the wind turbine would be at the exit of a long tunnel where the line speed is high

 

[E&W Lucas]

Ok, we've finished our project and I am assuming there is a small amount of drag (no idea how small). We are doing a presentation tomorrow and would like to have a rough idea of when a train begins to brake. 2 or 3 miles sound reasonable? (I'm pretty sure 125mph trains slow to 0mph with emergency brakes in 1.5 miles... I think!)

Any ideas would be appreciated!

Very very roughly, assuming roughly level track and dry rail conditions, for a controlled approach, think 1 mile from about 90moh, and 2 - 2 1/2 from 125 mph. (remember momentum is exponential). 125 in emergency, in favourable conditions approx 1 mile to stop.

But surely you would want your turbines where the linespeed is highest?

 

[ainsworth74]

But surely you would want your turbines where the linespeed is highest?

I was thinking that...

I don't your thinking as to why you want to place these where trains are braking, surely you want to place them at section where trains pass at speed? Or at speed through tunnels, you could get a fair bit of energy from the pressure wave travelling through a tunnel.

 

[O L Leigh]

You're surely going to get more power generated by the wind than from passing trains. The aerodynamic effect of a train passing is fleeting, not very powerful and unfocussed.

While I'm not engineer or designer, I just can't see how you will be able to meaningfully harness what energy is going to come your way, or what yields it will give you.

O L Leigh

 

[chuffchuff]

Stopping with a 375

Step 1 brake application is 3%g
" 2 " " " 6%g

g is the force of gravity

90mph about 1.3km