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-   -   UDF for defining a body force in Singel ROtating Reference Frame (http://www.cfd-online.com/Forums/fluent/72521-udf-defining-body-force-singel-rotating-reference-frame.html)

 teymourj February 9, 2010 02:06

UDF for defining a body force in Singel ROtating Reference Frame

Dear all,

I am trying to use Discrete Phase Model (DPM) to look at particle behavior in the solution of my Single Rotating Reference Frame (SRF) which contains my countinues fluid.

As long as SRF has rotating frames, therefore a Centrifugal and Coriolis term will be added to the equation of force balance of the particles. What I need to do, is writing a UDF which calculates these two forces. Then compile it with my model, so that it cancels those two additional forces.

I wrote a UDF based on UDF manual section 2.5.2 file:///usr/ansys_inc/v120/fluent//f...udf/node67.htm as follow, but it did not work out and I get error when I want to compile it. I was wondering if anyone can help me with that.

/* UDF for computing the force due rotating refrence frame on a particle */

#include "udf.h"
#define ROHR 1.5

/* density ratio of particles (roh/roh_p) */
#define OMEGA 1.78

/* Calculate some of centrifugal & coriolis force on a particle */
/* axis of rotation is "Y" and there are two force components in "X" and "Z" */ /* Fx= (1-ROHR)*OMEGA^2*x + 2*OMEGA*(u_z,p - ROHR*u_z), Fz= (1-ROHR)*OMEGA^2*z + 2*OMEGA*(u_x,p - ROHR*u_x) */

DEFINE_DPM_BODY_FORCE(particle_body_force,p,i)

{
real bforce=0;
if(P_TIME(p)>=TSTART)
{ if(i==0)

bforce=(1-ROHR)*OMEGA^2*P_INIT_POS(p)[0] + 2*OMEGA*(P_VEL(p)[2] - ROHR*rel_vel[2]);

else if(i==2) bforce=(1-ROHR)*OMEGA^2*P_INIT_POS(p)[2] + 2*OMEGA*(P_VEL(p)[0] - ROHR*rel_vel[0]); }

else bforce=0.0;

/* an acceleration should be returned */
return (bforce/P_MASS(p));

-teymourj

 teymourj July 28, 2011 13:46

Solution!

I found the solution to this problem. Read the MRF/SRF limitations for tracking particles in ANSYS FLUENT user's guide at:

// User's Guide :: 1 // 10. Modeling Flows with Moving Reference Frames // 10.3. Flow in Multiple Moving Reference Frames // 10.3.1. The Multiple Reference Frame Model

Note that the particle track in rotating reference frame for inert particles is MEANINGLESS (see the user's guide). You should use the TUI command to track particles and extract their data in absolute reference frame.

Best,

Teymour

 mingersai July 28, 2011 17:45

THANK YOU SO MUCH!!!!!!
That's why I can not get anyting. With rotating reference frame.
Ansys customer support seems to made a mistake, I had asked them whether I can inject particles without being affected by rotation reference frame and they said no......

I had been stucked here for a long time.