[samcfd]

Dear all,

I'm using a UDF for pitching airfoil . The function i'm using is

omega[2] = 0.5 * pitchampl * (1-cos(w*time));

pitchampl = 25 * pi/180;

w = 2 * pi * 0.15;

when i use this function the airfoil is rotating 360 deg. i dont understand y..

but when i use omega[2] = 0.5 * pitchampl * sin(w*time); its pitching perfectly...

Could some1 pls tell me y this is happening.

thanks in advance,

regards,
sam

[blackmask]

Note that omega is angular speed rather than the angle of attack. You angular speed is always non-negative so that your airfoil is always pitch in the same direction. You need something like
d 0.5 * pitchampl * (1-cos(w*time))
-----------------------------------
d time
which leads to
omega[2] = w*0.5 * pitchampl * sin(w*time);

[samcfd]

Originally Posted by blackmask

Note that omega is angular speed rather than the angle of attack. You angular speed is always non-negative so that your airfoil is always pitch in the same direction. You need something like
d 0.5 * pitchampl * (1-cos(w*time))
-----------------------------------
d time
which leads to
omega[2] = w*0.5 * pitchampl * sin(w*time);

Dear Blackmask,

Thanks for your reply. I really didnt get wat u were saying. I want the airfoil to pitch using

omega[2] = 0.5 * pitchampl * (1-cos(w*time));.

what changes do i make..


thanks in advance,
regards,
sam.

[blackmask]

I assume that you can tell the difference between pitch angle, say beta, and angular velocity, say omega. And you should know they are related by
omega[2] = d (beta) / dt (#)
While
beta(t) = 0.5 * pitchampl * (1-cos(w*time))
is the pitch angle in the above equation (#) (so that beta is in the range [0, pitchamp]), what you need to specify in the UDF is the angular velocity. That is what I tried to tell you in the last post.