🚀 go-pugleaf

"Richard Catlow" <RBCatlow@aol.com> wrote in message
news:d3979d5f.0209111108.4634cd7@posting.google.com...
> Tony Sayer asked
> >
> > Another very interesting bit of reading. Can you explain why the tunnel
> > would be significant please?. Is it to do with wind resistance perhaps.
> >
> The rolling resistance of a vehicle is governed by a number of factors
> called Davies coefficients in the form a+bv+cv^2
>
> Where a= static resistance of train to motion i.e. stiction
> b= rotary intertia
> c= aerodynamic drag
> v= velocity
>
> Thus a train in a tunnel has a higher c element of the equation as the
> turbulent air flow of the train interacts with the tunnel. The actual
> drag in a tunnel depends upon bore size, whether there is oncoming
> traffic in the same bore, speed, uniformity and smoothness of the
> tunnel bore surface, tunnel length, whether there are vents and their
> physical location etc. It all makes an interesting computational fluid
> dynamics problem, even more so if you have to control smoke flows as
> well. I spent a little time working for the CFD guru who looked at
> these problems for the Channel Tunnel - very absorbing it was too.

I know it's nothing to do with 3rd rail, but does any modern stock (air-con,
post-privatisation) have valves to shut off the pressure when the train goes
into a tunnel?  I seem to remember that Eurostar does, but does anything
like the Pendolino/Voyager/etc?

Angus