[mark yoe]

I'm newbie here. I got prob with dynamic mesh in FLUENT
can anybody help me on doing udf in order to make the rotor of the rotary engine cycle continuously in 360 degree

[Catthan]

Hi guys!

Mark yoe have you had any luck with the UDF?

I'm having the same problem myself..

Please post if you figured it out..
Thanks

Best wishes,
Thanos

[sonia.majd]

Hi to all
I am also trying to model the gas circuit in a Wankel engine,I cannot figure out the proper UDF to move the rotor CG along the eccentricity path and then rotate the rotor around its CG.
I have find a UDF (following code) that describe rotating of rotor respect to the geometric center of housing, but I’m cannot Define rotation of rotor respect to its own geometric center.

Code:
#include "udf.h"
#define r -0.0116 /*Eccentricity*/
float beta;
DEFINE_CG_MOTION(rotor, dt, vel, omega,time, dtime)
{
NV_S(vel, =, 0.0);
NV_S(omega, =, 0.0);
omega[2] = 314.16; /*angular velocity in rad/sec*/
beta = 942.48; /*angular velocity of rotor in rad/sec*/
vel[0] = -beta*r*sin(beta*time);
vel[1] = beta*r*cos(beta*time);
vel[2]= 0;
}

Can anybody please give me some guidance?
Best regards.
Sonia majd

[Catthan]

Hi Sonia,

the UDF you've found is the one everyone seems to be using.
It should be OK.

The velocity expressions are the obtained by differentiating the x and y coordinates equations as you know.

These include a part that "says" that the CG of the rotor moves on the periphery of a circle and the other part "says" that the tips follow the path of the peritrochoid.

So, differentiating those you get 2 velocity equations that should be all you need.


Check that your rotor has the proper dimensions, eccentricity particularly, and make sure you define you dynamic mesh settings correctly.

There's a lot to read about that in the users guide and the manual.

Make sure you compile the UDF correctly and that "rotor" appears in the rigid body drop down list for mesh motion. Have your rotor center coordinates in hand and you may need to play with the orientation angle.

Is your problem with meshing error (negative volumes etc) or is it that the rotor is not moving at all??


There are other Wankel threads in the Fluent and possibly UDF sections of the forum that would be a good read for you.

Also make sure that the tips or seals don't touch the housing. There needs to be a gap..
The issue with the gap at tips is that the bigger, the less problems you have in solving.. However, depending on the pressure gradients developed, there will be backflow and pressure loss. So you need to keep the gap small.
But you can worry about that later..

[sonia.majd]

Hi Catthan, I appreciate your attention and thanks for your guidance.
I’m solving three-dimensional flow in Wankel engine.
After compiling the user defined function (UDF) in Fluent and setting all the dynamic parameters and dynamic zones parameter’s when I check the dynamic mesh motion it is giving me the message of NEGATIVE VOLUME DETECTED .i.e. dynamic mesh update failed. What exactly it mean? How to minimize the negative volume?
I guess rotor center coordinates and its orientation angle is properly selected and I am using smoothing and remeshing and not layering.
Maximum cell skewness is 0.8 and I’m using two zones in dynamic mesh setting, rotor as rigid body motion and housing as stationary zone.
But I don’t know how to define cell height?
I would be pleased more, if you help me in this regard.

[amin.]

Hi All
I have the same problem of how to define the mesh moving for wankel engine with fluent.
I think this post is old but if it is possible, some one help me on this
Thank all

[K.Arimoto]

I am a beginner of analysis.
Currently, we are experimenting with a rotary engine, and we are going to analyze it. So, if you have experienced rotary engine, please help! !
If you can tell me in detail how to analyze the rotary engine in ANSYS R2, thank you.