[hlloydwilliams]

Hi,

I am trying to simulate an airfoil oscillating vertically over a 6m displacement. i want to write UDFs to describe different relationships between the pitch of the airfoil and the vertical displacement. first i am trying a sinusoidal relationship so the foil is at max angle of attack at the centre of the displacement and the there is also a spring force pulling it back to the centre of the range. the foil is a symmetrical NACA0012 of chord length 1m in a constant air speed of 10m/s
i aim to find the best pitch motion that will completes a complete oscillation the quickest.
to do this i am using an interpreted six degrees of freedom UDF shown below:

#include "udf.h"

DEFINE_SDOF_PROPERTIES(fmotion5, prop, dt, time, dtime)
{

real x[ND_ND];

real THETA[2];
real vel[ND_ND];

real a ;

#define PI 3.14159265;
real K=10;
real THETAMAX =0.349;
real SPRING;

SPRING=-K*(x[1]);

prop[SDOF_MASS] = 5;
prop[SDOF_IZZ] = 0.00001;


-3<=x[1]<=3;

prop[SDOF_ZERO_TRANS_X]=TRUE;
prop[SDOF_ZERO_TRANS_Z]=TRUE;
prop[SDOF_ZERO_ROT_X]=TRUE;
prop[SDOF_ZERO_ROT_Y]=TRUE;

prop[SDOF_LOAD_F_Y]=SPRING ;



a = ((vel[1])/(sqrt(vel[1]*vel[1])))*THETAMAX*cos(asin((x[1])/3));
THETA[2]=a;


}

I can only interpret the UDF due to the restrictions on the university computer i am using.

When i hook the UDF in, the airfoil shows no motion and i sometimes get negative cell volumes. Can anyone help me on this?

I am quite new to CFD by the way.

Thanks in advance
Henry