I'm starting to play with XFOIL a bit, just to compare lift/drag of
a few common foil sections at a Reynold's numbers from around
200,000 to 600,000.

What number should be entered as the mach number variable?
(this is for foils in water.... fresh water in particular).

Thx
Phil

What fraction of 1100 feet per second are you designing for?

Brian W

On Sun, 27 Jul 2003 12:43:06 -0400, "Phil Locker"
wrote:

I'm starting to play with XFOIL a bit, just to compare lift/drag of
a few common foil sections at a Reynold's numbers from around
200,000 to 600,000.

What number should be entered as the mach number variable?
(this is for foils in water.... fresh water in particular).

Thx
Phil

Brian says:

...or am I weaseling out? :-)

;-)
Nope! There _are_ very, very small effects at the surface that can "mimic"
compressibility (hence the really small Mach number used. Also, the speed of
sound in water is WAAYY higher than in air, I want to say in the order of 1800
ft/sec but I may be way off. It's faster - 'nuff said ;-)

So "Yes" there can be some effects, but it's a tough call, and if not actually
at the interface, it is best to zero out the Mach no.

Steve "dang, I feel technical today"
Stephen C. Baker - Yacht Designer
http://members.aol.com/SailDesign/pr...cbweb/home.htm

On 29 Jul 2003 11:21:32 GMT, ospam (Stephen Baker)
wrote:
/// the speed of
sound in water is WAAYY higher than in air, I want to say in the order of 1800
ft/sec but I may be way off. It's faster - 'nuff said ;-)
///
Steve "dang, I feel technical today"
Stephen C. Baker - Yacht Designer
http://members.aol.com/SailDesign/pr...cbweb/home.htm

1403 m/s on up with increasing temperature in fresh water
1536 m/s on up with increasing temperature in sea water.

Brian W

Brian says:

1403 m/s on up with increasing temperature in fresh water
1536 m/s on up with increasing temperature in sea water.


There - ya see? - a "1" with three numbers after it. I wasn't far off with
1800 f/s. (only a factor of 2.8-ish)
blushes....

Thanks, Brian.

Steve