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Draughting arrangements for Bulleid Pacifics including the Giesl ejector

Discussion in 'Steam Traction' started by jamesd, Oct 14, 2014.

  1. JJG Koopmans

    JJG Koopmans Member

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    That would depend on the Lempor nozzle inclination isn't it?
    Kind regards
    Jos
     
  2. Allegheny

    Allegheny Member

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    I think some would say that the existing Bulleid-Lemaitre already does this, but it is not an efficient diffuser.

    The only thing I can think of is to have an "annular chimney", which has a pipe up the centre with fresh air flowing up it from somewhere outside the locomotive.
    Obviously you would never design an exhaust system like this unless there is some particular reason for it, and it may be challenging to make it work efficiently.
    This would increase the total quantity of gas flowing up the chimney.
     
  3. Sheff

    Sheff Resident of Nat Pres

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    Just to clarify, we are talking about the chimney exit diameter, and not the blast nozzle here? As for the effect on financial contributions, speaking personally, I prefer to invest in new-builds which I feel are engineered with a view to maximising their reliability, efficiency and performance, so A1, P2 and Clan to date. Despite having friends involved, I chose not to invest in the Patriot project. I’m watching this one with considerable interest ......
     
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  4. srapley

    srapley New Member

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    Correct, chimney exit diameter, not blast nozzle, though the nozzle area may need increasing too. What is inside the smokebox is unseen so there's easier scope for changes. I am trying to do just that (maximise reliability, efficiency and performance) within the confines of the intent of returning GSN to "original" condition (air-smoothed with chain drivne valve gear), so please do keep an eye on us (and if you have any questions about our engineering plans/visions that you'd like answering please get in touch via our website contact form)...
     
  5. Allegheny

    Allegheny Member

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    I've recently become a member the GSNLRS as a result of this discussion. I don't consider myself particularly as a fan of the Southern, and aesthetically I prefer non-streamlined locomotives, but I like the principle of people trying to improve locomotives. If the modifications to the draughting are successful, I hope they will be copied onto other Bulleids.
     
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  6. srapley

    srapley New Member

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    Welcome onboard!
     
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  7. Big Al

    Big Al Nat Pres stalwart Staff Member Moderator

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    I take that to mean other Bulleids in original condition as there is no problem with the rebuilt variant. That said it's difficult to see how the cost/benefit analysis works for any loco not running on the main line.
     
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  8. Sheff

    Sheff Resident of Nat Pres

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    If locos aren’t going main line then all bets are indeed off.
     
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  9. Allegheny

    Allegheny Member

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    Too early to tell at the moment, but as someone mentioned earlier in this thread, it would be interesting to do a comparison with a rebuilt MN. I think there is still room for improvement with the front end efficiency of the rebuilt locomotives. Hopefully a full assessment will be carried out in the fullness of time.
     
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  10. class8mikado

    class8mikado Part of the furniture

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    Although the smoke boxes were changed i dont recall if the 'contents' were on the rebuilts ? in which case the same deficiences exist within the rebuilts, - they just have better smoke deflectors...
     
  11. srapley

    srapley New Member

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    The chimney was changed on rebuilding, it had a 26inch long, 6 degree diffuser, with a bell mouth entrance
     
    Last edited: Apr 9, 2021
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  12. Allegheny

    Allegheny Member

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    If my interpretation of post #122 (page 7) of this thread is correct, the revised chimney fitted during the rebuild gave an improvement in efficiency, but they could have gone further. Probably budget constraints applied at the time, and they decided that it was all they needed.
     
  13. class8mikado

    class8mikado Part of the furniture

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    Thanks - you learn a little everyday. If its not asking too much - Would be interested in your take on how the design of the airsmooth casing and the air scoop front of the merchant navy might actually hinder, rather than help to keep clear air down the Locomotive sides, and also the same for the original P2... both look like they should work and both make for a great looking locomotive, but...
     
  14. martin1656

    martin1656 Nat Pres stalwart Friend

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    Has anyone made a model of the MN air smoothed casing, and tested it in an wind tunnel yet, to see what can be done to improve the air flow and lift the steam and smoke upwards , what effect would a lip on the casing make just before, or after the chimney? or changing slightly the contour of the shape of the smoke deflector ?
     
  15. Sheff

    Sheff Resident of Nat Pres

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    Is the proposal to recreate the original casing (oh yes!) or the mass production version which included deflectors? If the latter, were these not effective? If not, it would be worthwhile modelling the airflow for different deflector/casing gaps, maybe try vanes in the gap etc.
     
  16. Big Al

    Big Al Nat Pres stalwart Staff Member Moderator

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    If GSN is going to appear one day as an unrebuilt MN then to my mind what you don't do is replicate what Tangmere looks like. You go for the original shape as in:

    upload_2021-4-10_12-2-10.png

    Can't see the need for all this debate about draughting. If main line crews could handle the locomotive in its original form on a West of England service as this snapshot shows, then trundling up and down a heritage line one day will be fine. And it will look distinctively different from other versions.
     
  17. nickt

    nickt Member

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    Yes, I know a guy who did a wind tunnel comparison of a original and a rebuilt for a degree project. If I recall, the original was marginally more streamlined.
     
  18. Sheff

    Sheff Resident of Nat Pres

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    Yes that! But it was known to be dreadful for lifting the exhaust ......
     
  19. Big Al

    Big Al Nat Pres stalwart Staff Member Moderator

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    .......as could be said for other big engines drifting around at 20/25 mph. That's my wider point. (Yes, I know that there are hills on some heritage lines.)
     
  20. fergusmacg

    fergusmacg Part of the furniture

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    I can see little point when they have already stated there are some modelling been done using CFD (Computational Fluid Dynamics) which if used correctly should allow all you would ever need in that area without tying up a wind tunnel or producing lots of differing physical models to get to an optimal solution.

    I have a feeling there's was a paper from the Institute of Locomotive Engineers on wind tunnel testing of steam locos if anyone's so interested in using old tech methods (obsolete?!) - my copies are buried in the loft so not easy to hand.


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