Modelling a propeller

Discussion in 'Props' started by Roflhat, Sep 24, 2015.

  1. Roflhat
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    Roflhat Thundercat - 70.10mph

    Hi,

    I'm studying Naval Architecture with high performance marine vehicles at the University of Strathclyde.
    For my fourth year project I want to model a surface piercing propeller, namely a through hub cleaver. I have an 11 x 18 pitch Mercury cleaver which I hope to use as the basis of my design. My aim in the future is to design and model my own propellers, but I would like to start by modelling and existing propeller.

    My plan is to get the propeller scanned and get as many figures from it as possible so I can model it. I hope to send it to a company in the UK for this.

    I want to model this propeller using CAD software and possibly modify the design slightly, I want the prop to use a removable hub kit so it can be replaced if damaged or for use on a different engine.

    I don't have much experience in this so any input is greatly appreciated. What software would you recommend? Do you think this is a feasible project?

    Thanks
     
  2. Roflhat
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    Roflhat Thundercat - 70.10mph

    Any suggestions on what file type would be best to receive the propeller in? I've found companies which can create a model of it by scanning it but I need to know what file type I need. Needs to work in Maxsurf, Rhino and AutoCAD.

    Thanks
     
  3. cmckesson
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    cmckesson Naval Architect

    Your description makes it sound as if you are wanting to model the _geometry_ of the propeller. But if you are intending to improve it's performance then it seems to me you will want to model it's fluid dynamics. This will require inputing the geometry into a CFD program.

    So I submit that the answer "how best to create the geometry model" can't be answered without knowing which CFD tool you intend to use.

    Best regards,

    Chris McKesson
     
  4. Roflhat
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    Roflhat Thundercat - 70.10mph

    Hi Chris,

    thanks for the reply. Yes at first my plan was to carry out a CFD on the propeller, however our advisor for the fourth year project thought this would be a bit ambitious. We haven't done at CFD before, this will be our first year looking at it.

    I think for this project my aim is just to model the existing propeller, once I've done that I can look into modifying the design and doing some CFD, but this will be most likely in my own time.

    Cheers
     
  5. Joakim
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    Joakim Senior Member

    CFD modelling a surface piercing propeller is way too ambitious, if you don't have any experience in CFD. A submerged propeller would be much easier, but still not easy at all, especially with cavitation.

    I have done what you are planning about 20 years ago. We took a propeller to a company for scanning and received it as a IGES surface. Then I made a grid from it for a CFD software and did the simulation with the multiple reference frame model (very new model back then).

    It wasn't really a marine propeller, but very similar to it. It was a submerged impeller used in a mixing tank. We also made some laser doppler flow field measurement and compared the flow field and turbulence levels to the simulations. The results were very good regarding thrust, torque and flow field, but not that good for the turbulence levels.

    Later we got even better results, since we could use much denser grids due to much faster computers.
     
  6. Roflhat
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    Roflhat Thundercat - 70.10mph

    Thanks, I guess that's CFD out of the question for now at least.
    Sounds like a really interesting project, did you modify the propeller once you had the file?
    Looks like IGES is the file type to go for, as it can be imported and exported between all the programs available on the University computers.
     
  7. cnnammu
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    cnnammu New Member

    Hi,Roflhat

    There is a software called " PropCad " which is specialized for designing and modelling geometry of propeller from HydroCom. I think it's very useful and easy to model a propeller after you have decide about pictch & dia., within a short time. It can be easily output as a lot of formats that you can continue CFD calculation using such that friendship system like opensoure software.
    But using rhino & maxsurf, it can be done for modelling but i think it will be take time.
     

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  8. Roflhat
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    Roflhat Thundercat - 70.10mph

    Hi,

    yeh I was looking at Propcad, it looks perfect for what I need but unfortunately they don't do a student deal unless the University purchases the program. I might send them an email and see what the deal is, it looks ideal.
    Have you used Propcad?

    Cheers
     
  9. Joakim
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    Joakim Senior Member

    No we didn't modify the propeller. The goal was not to optimize it, but to verify our mixin vessel modelling scills. We modelled several other impeller types as well, but they were much simpler and there was no need for scanning, since the drawing was enough.

    IGES is one option, STEP is another and even a point cloud (as x,y,z) could be OK. Or maybe an AutoCAD file?
     
  10. Roflhat
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    Roflhat Thundercat - 70.10mph

    Alright. I think the only part I'm going to change is the hub, so I can use a removable hub kit.
    The company I'm talking to at the moment says they can do any of those files types, except for AutoCAD, which is .dwg I think? But IGES should be fine. Just need to send them more dimensions and pictures for a quote
     
  11. Roflhat
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    Roflhat Thundercat - 70.10mph

    If anyone can recommend good books to read on this topic that would be appreciated, related to surface-piercing propeller design.

    Thanks
     
  12. Roflhat
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    Roflhat Thundercat - 70.10mph

    update on this, sent the propeller away, 11x18p Mercury Cleaver. Got the IGES file back a few days ago, here's a couple screenshots from Rhino
    [​IMG]

    [​IMG]

    I've bought a 13 spline RUBEX hub which I'm going to use as a reference to model around, I'll start modifying the design hopefully towards the end of January
     
  13. Roflhat
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    Roflhat Thundercat - 70.10mph

    I'm just starting on this now, anyone have any advice regarding extrapolating the blade shape further into the hub? I want to remove the fillet where the blade joins the outside of the hub and move it inside the exhaust tube, with the blade continuing through.
    Here's a photo of a propeller which looks like what I'm aiming for.
    [​IMG]
     
  14. gonzo
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    gonzo Senior Member

    Removing the exhaust hub will increase turbulence and ventilate the propeller. Are you trying to modify an outboard propeller to run on a straight shaft?
     

  15. Roflhat
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    Roflhat Thundercat - 70.10mph

    I'm not removing the exhaust hub, it's remaining a through-hub exhaust propeller. It's a propeller from an outboard, which I am modifying, but it is still going to (hopefully) fit the same outboards as the original.
     
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