[ronak]

Hi
I'm simulating an unsteady harmonic 2D motion(pitching) for an airfoil in Fluent using a UDF. The amplitude of pitching is 15deg,the angle of attack is 10deg. trying to validate with a paper but the result doesn't match. The lift coefficient range is between -0.5<Cl<2.4 in the paper but the lift Coeff. range of my simulation is 0.1<Cl<2.3
I doubt in my mesh so I tried many mesh and time steps, still there is no negative lift.I'm using this UDF:
#include "udf.h"
DEFINE_GRID_MOTION(airfoil,d, dt, vel, omega, time, dtime)
{
real a, w, pi;
pi = 3.14159265;


/* define motion variables */
a = 15*(pi/180); /* Amplitude */
f=0.06; /* frequency */
w = 2 * pi *f; /* Angular Frequency */


/* define airfoil motion */
omega[2] = -a*w*cos(w*time); /* z-component of angular velocity */


}

The angle of attack is defined in inlet velocity ( in monitors, lift monitors & drag monitors)

Why is the lift positive whole the cycle although we're expected to have a range of negative lift as the airfoil moves anticlockwise from 10deg to -5deg and returns in a clockwise direction & continue to 25deg.
what could be my mistake?
The result of the paper is attached.

Thanks in advance

[maisui1993]

may be the cg-motion is ok

[moh_zain]

use CG motion not grid motion the code is fine just change grid motion with CG motion

[ronak]

Originally Posted by moh_zain

use CG motion not grid motion the code is fine just change grid motion with CG motion

Thank a lot.