Unusual Foil Requirement - Thoughts?

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!

 

c/t of 4, correct?
lifting or non-lifting?

 

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.

 

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.

 

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?

 

I'd use a TMB-EPH shape. What you need is exactly what it was designed for...low lift, low cavitation, and fat.

 

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.

 

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.

 

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

 

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...

 

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?

 

Your requirements lead towards a body of revolution, a submarine-body or a dolphin-body shape, rather than towards a foil. See this paper too: http://cafefoundation.org/v2/pdf_tech/Drag.Reduction/5.AIAA-48131-445.pdf

 

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.

 

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.

 

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.