Hydrofoil exercise to validate CFD analysis

Discussion in 'Hydrodynamics and Aerodynamics' started by quequen, Oct 1, 2014.

  1. Mikko Brummer
    Joined: May 2006
    Posts: 486
    Likes: 33, Points: 28, Legacy Rep: 258
    Location: Finland

    Mikko Brummer Senior Member

    Thanks Doug, even if Hugh's explanation is not the clearest, an outward L could have its merits in some cases. Patrick, if you are still there, how about flipping the vertical strut around in your 3DFoil model, to see just how much in drag one has to pay.
     
  2. nico
    Joined: Jan 2003
    Posts: 190
    Likes: 6, Points: 0, Legacy Rep: 52
    Location: SF

    nico Senior Member

    Yes, agree with this.
    Needs to be done at the begining of every new process, but not every new geometry. The software companies sometimes themselves provide such test cases with geometries and validation.

    Yep, so then why go the Ranse way? takes longer, more expensive, requires more power to run,... There are some very good tools for preliminary design, and opensource ones; XFLR5, AVL,... I don't think the basic Ranse give really more insight than those basic tools.
    Better Ranse simulation with transition, cavitation modelling with detailed geometries will then help you refine things.

    Tough one, changes day to day and every software has its own way.
    We all expect a certain amount of laminar flow, I'd test different values of ambient turbulence to correlate your simulation to the expected amount of laminar flow (e.g. 15% of the chord). This ambient turbulence value can then be used to compare geometries together.
     
  3. quequen
    Joined: Jul 2009
    Posts: 369
    Likes: 15, Points: 28, Legacy Rep: 199
    Location: argentina

    quequen Senior Member

    What about transition at the hinge? In an inward L the same profile goes all around the path giving the beautiful pressure distribution seen on the pictures, but in an outward L you must change from suction on the upper side of the horizontal branch to suction on the inner side of the vertical one.That transition should have a high cost on efficiency.
     
  4. quequen
    Joined: Jul 2009
    Posts: 369
    Likes: 15, Points: 28, Legacy Rep: 199
    Location: argentina

    quequen Senior Member

    Just for the fun of learning! Right now kids at highschool are using FEA tools to understand basic phisics. Something alike will happen with CFD, may be on the next ten years, may be sooner. The assumptions and complexities that still make CFD setup a very difficult and professional task, may be automatized inside software's architecture in the near future ;)
     
  5. quequen
    Joined: Jul 2009
    Posts: 369
    Likes: 15, Points: 28, Legacy Rep: 199
    Location: argentina

    quequen Senior Member

    About flying the virtual moth, attached is a file that could be a basic sail and mast (twist and shape are approximations only)

    -
     

    Attached Files:

  6. Mikko Brummer
    Joined: May 2006
    Posts: 486
    Likes: 33, Points: 28, Legacy Rep: 258
    Location: Finland

    Mikko Brummer Senior Member

    Thanks Quequen, looks good, even if it lacks mast side bend, which there must be in reality. I could easily use it as a base for my own model, but if you could send me the Solidworks file it would be even easier?

    Then I would still need the wings on the hull (trampolines)... ;-)

    About the T-foil, I haven't had the time to really look at it yet, but I think eventually I will want the flap separate from the foil, to be able to adjust it for the ride height. There, too, would be easier to work directly on the S-works file, unless you feel like doing it.
     
  7. quequen
    Joined: Jul 2009
    Posts: 369
    Likes: 15, Points: 28, Legacy Rep: 199
    Location: argentina

    quequen Senior Member

    Mikko, I'll try to split the T-foil and leave the flap as a separated part.

    This are my outcomes for the Vendor2 appendages. T-foil flap is not deflected.

    Velocity: 8 m/s
    Lift Load distribution: T-foil: 61%, Rudder: 39%
    Total Lift: 1218 N
    Total Drag: 197 N

    At this speed, Lift easily overcomes the Hungry Beaver design weight. So the question is how do they control excessive lift at higher speeds ?.
     

    Attached Files:

  8. Mikko Brummer
    Joined: May 2006
    Posts: 486
    Likes: 33, Points: 28, Legacy Rep: 258
    Location: Finland

    Mikko Brummer Senior Member

    With the wand, controlling the flap, and with their own weight, controlling the pitch and with it the lift from both foils. What interests me is:

    - are both the T-foil and the rudder lifting most all of the time?

    - is the flap on the T-Foil most of the time deflected to increase lift from the T-foil, or to decrease it? As I recall, I saw one T-foil-flap arrangement where the gap between the foil and the flap was sealed with sikaflex on the underside, not from the upper (suction side) as one would expect.
     
  9. SukiSolo
    Joined: Dec 2012
    Posts: 1,270
    Likes: 25, Points: 0, Legacy Rep: 271
    Location: Hampshire UK

    SukiSolo Senior Member

    On National 12s' the (fixed ie no flap) T Foil rudder is pivotable in the fore/aft sense. It allows the hull to carry on planing and can also promote early planing depending on attitude. I am reliably informed that it also improves upwind performance a lot, so I would surmise it allows less rig pitch (on 12s') and greater efficiency from the sails.

    The Moths are a different because they 'fly'!. However it would make sense if similar factors are at work, just faster. So very sensible questions Mikko, for this very interesting discussion.
     
  10. tspeer
    Joined: Feb 2002
    Posts: 2,204
    Likes: 171, Points: 63, Legacy Rep: 1673
    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    And there was a beam limit in the class rule. Since the hulls were already at maximum beam, there was nowhere else to go but inward.
     
  11. quequen
    Joined: Jul 2009
    Posts: 369
    Likes: 15, Points: 28, Legacy Rep: 199
    Location: argentina

    quequen Senior Member

    With 4º of leeway :
     

    Attached Files:

  12. Mikko Brummer
    Joined: May 2006
    Posts: 486
    Likes: 33, Points: 28, Legacy Rep: 258
    Location: Finland

    Mikko Brummer Senior Member

    You could now compare against the raw data in Beaver's CSYS paper, p. 17.
     
  13. PatHanley
    Joined: Oct 2014
    Posts: 7
    Likes: 1, Points: 0, Legacy Rep: 23
    Location: United States

    PatHanley Junior Member

  14. gigi
    Joined: Feb 2013
    Posts: 7
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: Croatia

    gigi Junior Member

    Does somebody know where paper from post #2 can be downloaded?
     

  15. tspeer
    Joined: Feb 2002
    Posts: 2,204
    Likes: 171, Points: 63, Legacy Rep: 1673
    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    I don't think you can download it. You could purchase the proceedings for the 11th CSYS.
     
Loading...
Similar Threads
  1. container
    Replies:
    7
    Views:
    313
  2. vejas
    Replies:
    34
    Views:
    1,931
  3. revintage
    Replies:
    8
    Views:
    734
  4. revintage
    Replies:
    14
    Views:
    1,947
  5. rallyhybrid
    Replies:
    39
    Views:
    1,957
  6. optiwings
    Replies:
    1
    Views:
    604
  7. Tommifin
    Replies:
    5
    Views:
    822
  8. Ittiandro
    Replies:
    2
    Views:
    1,710
  9. bjn
    Replies:
    23
    Views:
    2,613
  10. Tommifin
    Replies:
    3
    Views:
    1,362
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.