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Draughting arrangements for Bulleid Pacifics including the Giesl ejector

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

  1. fergusmacg

    fergusmacg Resident of Nat Pres

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    Nah, just use those new fangled LED lights that we all know produce much more light with less current . . . . . . (Don's hard hat and runs)
     
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  2. Allegheny

    Allegheny Member

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    I'm just wondering if it would have been clearer for some people if the discussion was about improving the "front-end efficiency" rather than improving the draughting. The two are very closely related.
     
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  3. srapley

    srapley New Member

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    Apologies for slow response, been offline for a few days. My idea with keeping the original outer diameter is to keep the external appearance of the locomotive the same as original, makign a known compromise in performance to not compromise appearance. As one of the other comments alluded to, if we can keep the same performance whilst improvign smoke clearance, that is a good starting point. The names I've used are generic, it's to give some impression to the reader-a Lemaitre is the original exhaust, the Lempor I discuss has a longer diffuser than the Bulleid-Lemaitre, but is really a middle ground between the two, the Giesl is an oblong ejector.
     
  4. srapley

    srapley New Member

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    I believe Swanage's middle cylinder has been/is being replaced. The draughting question is part of raising interest in the project in the next generation of engineers, and when we manufacture the new cylinder, it would be a good idea to know what we're doing with the draughting so we can link the two together. The analysis of the draughting is being supported by the GSNLRS/GSNCIC, but we're not conducting it or financing it, as it is a Uniersity project.
     
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  5. srapley

    srapley New Member

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    Thanks Allegheny. For clarity, Loughborough is doing the CFD/aerodynamic study, Birmingham is doing the FEA on the crank axle. And yes, I'm doing this in my spare time.
     
  6. 30854

    30854 Resident of Nat Pres

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    You do realise if you'd done that, we'd by now likely be fruitlessly arguing the pros and cons of Scharfenberg couplings! :D
     
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  7. Allegheny

    Allegheny Member

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    I've looked it up on Wikipedia, but I think the Merchant Navy would be too powerful for it.:)

    Edit :- We could have a discussion on the effects of front end efficiency of the difference between inside admission and outside admission valvegear, which, if I've got it right, is the reason for replacing the middle cylinder.
     
    Last edited: Apr 7, 2021
  8. Sheff

    Sheff Resident of Nat Pres

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    Thanks for the reply. I’d have thought with the existing chimney you could have any exhaust you like, and just plate over the unused portion of the existing chimney? Only people on over bridges and drone pilots would be able to see?
     
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  9. Allegheny

    Allegheny Member

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    I think you would notice the difference in appearance of the smoke coming out of the chimney. From the video of City of Wells the appearance of the exhaust is clearly different from the Lemaittre fitted locomotives.

    Unless of course it's Repton, where the plywood will probably catch fire.:)
     
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  10. Sheff

    Sheff Resident of Nat Pres

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    I did think of that, but couldn’t get very interested
     
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  11. Allegheny

    Allegheny Member

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    If you're intending to stop the smoke drifting across the locomotive, it will inevitably look different.
     
    Last edited: Apr 8, 2021
  12. Sheff

    Sheff Resident of Nat Pres

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    Indeed. And it’s not like you can see really see the chimney on a Spamcan.
     
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  13. Hirn

    Hirn Member

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    Controlling lineside fires by over draughting to shoot any bits of burning char up so high that they have burnt out and cooled off by the time they they come down is a very good example of a practical consideration which one might overlook and simply does not arise most of the time. The payment for the commercial forestry that Hogwarts Hall sent on fire when Harry Potter was filmed over the West Highland was thoroughly north of a million pounds and, I presume, reverberates to this day in insurance premiums.

    On the same basis: the Gisel ejector is superseded as the most efficient front end but it lifts the
    exhaust well over the engine and if this saves any incidents from drifting steam and critical stopping points missed that could be well worth while financially in the long term.
     
    Last edited: Apr 8, 2021
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  14. srapley

    srapley New Member

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    That would only be a possibility if the new design had a smaller opening than the existing, which is unlikely-I'm likely to recommend a compromised exhaust if I maintain the existing outlet diameter. And yes, it may only be visible by drone pilots and people on bridges, but they still may contribute financially to our project
     
  15. Allegheny

    Allegheny Member

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    I'm a bit puzzled by this. If one of the objectives is to blow the exhaust clear of the locomotive, for visibility reasons, you would want to increase its velocity. This means reducing the diameter of the chimney.
     
  16. class8mikado

    class8mikado Part of the furniture

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    Is that ... a Giesl-organ ?
     
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  17. class8mikado

    class8mikado Part of the furniture

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    Indeed, and if its agreed that the original merchant navies were not good at smoke clearance then something needs to be done about that. This will undoubtedly either change the appearance ( Nay, nay and thrice...) - or need a stronger exhaust, a stronger exhaust will increase cylinder back pressure.. unless a change to the exhaust system is made and.... back to page 1.
     
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  18. class8mikado

    class8mikado Part of the furniture

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    Its quite possible to reduce the internal diameter of a chimney without changing its external appearance like a shallow bell mouth but at the other end ( Bell exit ? Bell out, ? Bell top ? Bell end ? )
     
  19. JJG Koopmans

    JJG Koopmans Member

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    An other possibility is to guide the flow along the chimney in a way that the lowered pressure does no harm, Since Srapley is an aerodynamicist he knows the tricks!
    For myself I am wondering.
    Kind regards
    Jos
     
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  20. srapley

    srapley New Member

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    Depends how the exhaust interacts with it's surroundings; the analysis with a longer diffuser shows less obscuration, partially because it appears to be producing less turbulent mixing just behind the chimney exit. This is likely due to the flow detaching in the diffuser in the Bulleid-Lemaitre exhaust, unlike in the "Lempor"
     
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