# Specifying axis of rotation

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 August 14, 2007, 05:19 Specifying axis of rotation #1 David Banks Guest   Posts: n/a Hi everyone I have a turbine model whose axis of rotation is parallel with the X-axis (it sits 10m above it). When you are choosing values for your fluid zone/wall, how do you specify where the axis is? I am inputting a unit vector value of 1 in the X tab but this isnt relating to the real axis Any help would be great David

 August 15, 2007, 04:22 Re: Specifying axis of rotation #2 tom Guest   Posts: n/a I had the same problem, but the rotation axis wasn't even parallel to one of those in Fluent. So i went back and created the geometry again. But in your case I think it is not necessary. Try to specify the rotation-axis origin.in order to do this you must pick any point on your axis and check its coordinates.

 August 15, 2007, 05:14 Re: Specifying axis of rotation #3 David Banks Guest   Posts: n/a Tom How do I specify the rotation axis origin? Is this done in Fluent?

 August 15, 2007, 05:50 Re: Specifying axis of rotation #4 tom Guest   Posts: n/a yes in Fluent, define -> boundary conditions -> zonename -> you will open the window for defining boudary conditions for the zone you are interested in. rotation-axis origin panel is just next to rotation-axis direction panel.

November 5, 2016, 14:35
#5
New Member

Guoqing Zhang
Join Date: Nov 2016
Posts: 2
Rep Power: 0
Quote:
 Originally Posted by David Banks ;144451 Hi everyone I have a turbine model whose axis of rotation is parallel with the X-axis (it sits 10m above it). When you are choosing values for your fluid zone/wall, how do you specify where the axis is? I am inputting a unit vector value of 1 in the X tab but this isnt relating to the real axis Any help would be great David
Hi, David, I had the same problem that sepecify the rotational axis of arm which is parallel with the Z-axis in DEFINE_CG_MOTION. I found a may-helpful solution as shown below, but unfortunetly it didn't work as i expected. Did you solve the problem? If yes, could you send me a e-mail? guoqingzhang_1989@126.com. Thanks a lot.

# include "udf.h"
# define a0 15791.0742
DEFINE_CG_MOTION(arm_motion,dt,cg_vel,cg_omega,tim e,dtime)
{
real NV_VEC(axis), NV_VEC(origin);

NV_D(origin, =, -37.32952, 5.627642, 0.0);
NV_D(axis, =, 0.0, 0.0, 1.0);

if(time>=0&&time<0.003)
{
cg_omega[2]= -a0*time;
}
else if(time>=0.003&&time<0.007)
{
cg_omega[2]= -a0*0.003;
}
else if(time>=0.007&&time<0.010)
{
cg_omega[2]= -(a0*0.010-a0*time);
}
else if(time>=0.020&&time<0.023)
{
cg_omega[2]= a0*(time-0.02);
}
else if(time>=0.023&&time<0.027)
{
cg_omega[2]= a0*0.003;
}
else if(time>=0.027&&time<0.030)
{
cg_omega[2]= a0*0.010-a0*(time-0.02);
}
}

November 21, 2016, 08:38
#6
Senior Member

Kushal Puri
Join Date: Nov 2013
Posts: 183
Rep Power: 11
Quote:
 Originally Posted by David Banks ;144451 Hi everyone I have a turbine model whose axis of rotation is parallel with the X-axis (it sits 10m above it). When you are choosing values for your fluid zone/wall, how do you specify where the axis is? I am inputting a unit vector value of 1 in the X tab but this isnt relating to the real axis Any help would be great David
just find the center of the rotor and define vector as it is parallel to x axis

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