Unusual Foil Requirement - Thoughts?

Discussion in 'Hydrodynamics and Aerodynamics' started by PI Design, Jul 19, 2012.

  1. PI Design
    Joined: Oct 2006
    Posts: 673
    Likes: 21, Points: 0, Legacy Rep: 328
    Location: England

    PI Design Senior Member

    Hi,

    I have an unusual foil brief. I thought I would throw it open to ideas for appropriate sections.

    It needs to be highly buoyant (so tending towards a fat section, >25%), low drag and low lift ( for AOA 0-10 degrees). It also has to be very low aspect ratio, no more than 1.0. Reynolds number approximately 1.5e6.

    Any thoughts on suitable sections very welcome!
     
  2. jehardiman
    Joined: Aug 2004
    Posts: 3,323
    Likes: 741, Points: 113, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    c/t of 4, correct?
    lifting or non-lifting?
     
  3. PI Design
    Joined: Oct 2006
    Posts: 673
    Likes: 21, Points: 0, Legacy Rep: 328
    Location: England

    PI Design Senior Member

    Hi,

    Yes, c/t of 4 or less. Would like no, or very little, lift. I have thought about a cylinder with a hinged, weather cocking, flap but would like no moving parts if possible.
     
  4. Tim B
    Joined: Jan 2003
    Posts: 1,438
    Likes: 59, Points: 0, Legacy Rep: 841
    Location: Southern England

    Tim B Senior Member

    What are you designing? it sounds like the stub tank on old flying boats (where interior volume was a constraint). I'm struggling to think of anything else which would produce your requirements.

    Typically, the structure dictates the section thickness, and the operating Cl governs the planform area. Hence you end up with small(ish), thin foils.

    If you have no fluid-dynamic requirement for this appendage, a cylinder faird into the hull might suffice, but without knowing the purpose it's hard to advise.

    Tim B.
     
  5. PI Design
    Joined: Oct 2006
    Posts: 673
    Likes: 21, Points: 0, Legacy Rep: 328
    Location: England

    PI Design Senior Member

    Sorry, I don't think I can say more about the design. But fundamentally it needs to be low drag, low lift, fat and low aspect ratio. Is that an impossible combination?
     
  6. jehardiman
    Joined: Aug 2004
    Posts: 3,323
    Likes: 741, Points: 113, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    I'd use a TMB-EPH shape. What you need is exactly what it was designed for...low lift, low cavitation, and fat.
     
  7. sottorf
    Joined: Sep 2007
    Posts: 192
    Likes: 20, Points: 0, Legacy Rep: 202
    Location: South Africa

    sottorf member

    it sounds like you are designing somehting like Navatek ships already developed. See http://www.navatekltd.com/seaflyer.html You can find details of the system in the US patent office website. They have already patented the optimum configurations.

    I suggest you contact them or Robert Gornstein (retired). He might be more willing to share info with you than Navatek themselves.
     
  8. PI Design
    Joined: Oct 2006
    Posts: 673
    Likes: 21, Points: 0, Legacy Rep: 328
    Location: England

    PI Design Senior Member

    Thanks for that. I followed up the tmb-eph and found myself back here reading through a thread between you and Tom Speer about one of his section that looks promising.
     
  9. jehardiman
    Joined: Aug 2004
    Posts: 3,323
    Likes: 741, Points: 113, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    For what Tom and I were discussing about thickness aft, see this report for the data.

    FREE-STREAM CHARACTERISTICS ,OF A FAMILY OF LOW-ASPECT RATIO, ALL-MOVABLE CONTROL SURFACES FOR APPLICATION TO SHIP DESIGN; L. Folger Whicker, et al, David Taylor Model Basin, Washington, D. C., December 1958.

    http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA014272
     
  10. BMcF
    Joined: Mar 2007
    Posts: 1,073
    Likes: 94, Points: 48, Legacy Rep: 361
    Location: Maryland

    BMcF Senior Member

    Do mean something like what we built and tested as shown in the pic below? Extremely low aspect ratio but with some dynamic lift in addition to its bouyant lift...
     

    Attached Files:

  11. PI Design
    Joined: Oct 2006
    Posts: 673
    Likes: 21, Points: 0, Legacy Rep: 328
    Location: England

    PI Design Senior Member

    I'm having a good read right now, thanks

    Yes, something almost exactly like that shape would be great. Can you give me any details, BMcF?
     
  12. daiquiri
    Joined: May 2004
    Posts: 5,372
    Likes: 255, Points: 93, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

  13. DCockey
    Joined: Oct 2009
    Posts: 5,113
    Likes: 564, Points: 113, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    I agree with daiquiri. At an Aspect Ratio of 1 the flow and a thick section the flow will be fundamentally three dimensional which considerably complicates the analysis.
     
  14. PI Design
    Joined: Oct 2006
    Posts: 673
    Likes: 21, Points: 0, Legacy Rep: 328
    Location: England

    PI Design Senior Member

    Thanks for the paper Daiquiri. A body of revolution may not (but may, I need to check) fit in the spatial constraint. But perhaps two bodies in a catamaran configuration may be the answer. There would be relatively high skin friction and interference drag, but might still be the best compromise.
     

  15. BMcF
    Joined: Mar 2007
    Posts: 1,073
    Likes: 94, Points: 48, Legacy Rep: 361
    Location: Maryland

    BMcF Senior Member

    Aren't many to give, really; those are bouyant bodies, of course, but are shaped with some positive camber fore-aft to produce dynamic lift..so the shape is a "quasi" hydrofoil in the sense that it produces both dynamic and static/bouyant lift when moving through the water.
     
    Last edited: Jul 24, 2012
Loading...
Similar Threads
  1. Windmilljohn
    Replies:
    18
    Views:
    5,719
  2. S V
    Replies:
    0
    Views:
    1,048
  3. Mikko Brummer
    Replies:
    34
    Views:
    3,461
  4. rafa_racer
    Replies:
    0
    Views:
    838
  5. tlouth7
    Replies:
    16
    Views:
    2,143
  6. Eytan Levi
    Replies:
    0
    Views:
    1,052
  7. RogerO
    Replies:
    2
    Views:
    777
  8. Christian Lucas
    Replies:
    1
    Views:
    760
  9. RogerO
    Replies:
    18
    Views:
    1,698
  10. 14berlin
    Replies:
    4
    Views:
    1,894
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.