Low reynoldsnumber rudder

[magelh]

I am building a new rudder to my 2,4mR sailboat. It is my intention to try a deeper narrower profile than the old rudder.
Cordlength will be from 100mm to 190mm resulting in a rudder rarely exeeding
reynolds no. over 500.000.
Does anyone out there have any valid experience to share in this case?

Hasse

[jehardiman]

Expect a slightly higher coefficient of lift at very small aoa, a lower maximum coefficient of lift, a higher coefficient of drag, and a much lower stall angle but a less dramatic stall effect. Things in real world situations get really iffy in this area (Rn 10^5 through 10^6) because of the laminar-turbulent seperation-attachment effects which really scatters the data.

[Tim B]

Check out Mark Drela's X-Foil for work in this sort of reynolds number. It is known to be pretty good in air, and the last time I checked it against the CFD (in water) it was so good that I used it for all the low-angle-known-not-to-be-cavitating work.

However, it is written for low-speed applications in air, so it will not handle cavitaion. The trick is to work out the cavitaion Cp first, then the valid cases are those that do not exceed that Cp.

Best of luck,

Tim B.