[lfla]

Hi everyone!

I am studying 2D transient dynamic stall on a s809 as part of my masters and I was hoping for your assistance. I am using this formula to control the oscillations:

alpha(t)=alpha(0)+alpha(1)sin(2*pi*f*t). where alpha(0)=mean angle 8deg;

alpha(1)=5.5deg oscillation amplitude; f=1.2Hz; Ufreestream=30m/s

I have used the following interpreted udf and added it to the inner rotating domain under mesh motion.

#include <stdio.h>
#include <math.h>
#include "udf.h"

DEFINE_CG_MOTION(airfoil_pitch, dt, vel, omega, time, dtime)
{
real pitchampl, pitchdispl, omg, pi, count;

pi = 3.14159265;


/* reset velocities */
NV_S(vel, =, 0.0);
NV_S(omega, =, 0.0);

/* motion */
pitchampl = 5.5 * pi / 180; /* angular pitch amplitude */
omg = 2 * pi * 1.2; /* angular frequency */
pitchdispl = pitchampl * sin(omg * time); /* resultant displacement */

omega[2] = pitchampl * omg * cos(omg * time);
}
However this wont take into account the mean angle, has anyone done something similar. if this udf is correct perhaps i am inputting it incorrectly in the fluent gui.

so should i define the freestream at the inlet with respect to that mean angle ; Components >> x_vel=30cos8 and y_vel=30 sin8.

Also, how could i find what the angle of attack is for each time step?

Thanks in advance for any help.

P.S. If you would prefer to contact me via email instead of this thread please contact me at flanagl1@tcd.ie.

[lfla]

Has anyone done something similar with dynamic stall modelling on an airfoil using fluent, do i also need to set a sinusThank youoidal osillating freestream?

[ronak]

Have you overcome to the problem? Is the UDF correct?

[lfla]

The udf is correct for defining the motion of the airfoil. First step is to interpret it and then apply it to the airfoil or to the domain depending on what you keep fixed.

[litzj]

how about using compiled instead of interpret

[ronak]

I want to have a motion for whole the domain, airfoil moves and rest the domain moves together. Actually I compiled this UDF but it seems that there is no motion,judging by the animation.
What do you think?

[lfla]

Originally Posted by ronak

I want to have a motion for whole the domain, airfoil moves and rest the domain moves together. Actually I compiled this UDF but it seems that there is no motion,judging by the animation.
What do you think?

I'm not really sure why you want to rotate everything because in that case you wont represent the flow over a pitching airfoil unless you define your inlet according to a sinusoidal function. You should be able to preview the motion and the mesh you have used.

[ronak]

I want whole the domain to move because of 2 reasons :
1- If the whole moves,the size of all cells would be the same and I wont have some cells with high A.R or bad skewness
2- I'm going to valid with the attached paper.( Dynamic Stall .... ) in this paper there is a pitching motion for whole the domain.

[litzj]

how about write full component of speed and angular speed?

vel[0]=0
...

omega[0]=0
...
omega[2]=what you want

[litzj]

or made motion at the dynamic mesh panel

without remesh or layering

[ronak]

Hi
I tried to simulate a pitch motion as I mentioned before in this thread. Although I tried several UDF, Ive been working on one of them at the momemt,a CG_MOTION one.
The UDF has been compiled correctly. The values are acceptable but the lift coefficient and drag coefficient plots are not harmonic. I wish to validate with this paper : 'Dynamic stall simulation of a pitching airfoil under unsteady freestream Velocity' . I attached some screenshots of simulating with Ansys.
It's best to know that :
freestream velocity=1.89
omega=0.37
rotation amplitite=15 deg
The point is that in this case it's going to move whole the domain

I'll appreciate if you take a look and tell me what is wrong of the process.

[mahdihasan]

Did it work? Was the motion harmonic? I have a similar type of UDF but my the body is rotating 360 degrees

[ronak]

what kind of harmonic motion are you going to simulate?