For Joe : CFD in a Wankel engine
 

Hi Joe, I posted a message on the forum a few months ago for a problem with flow simulation in a Wankel engine. In your answer to me, you sais that you were setting up problems in which you considered flows in such a Wankel engine. Did you succed ? I've been working a lot on the leakage problem between the 3 chambers (dut to the fact that you can't close the volume when you're using dynamic meshing). I found some solutions, but none of them seemed to be really suitable. Now I'm working on only one wankel chamber to try to avoid leakage and close the volume.I was wondering if you've find a way to simulate the flow without inter-chamber leakage ?

Re: For Joe : CFD in a Wankel engine
 

Like I said before you have to use an artificial, imposed momentum source near the rotor tips to force localised fluid quiescence.

You know where the rotor starts, you know how it moves with time ... so you know where the rotor tips are at any point in time. Ergo, you can define this localised momentum source to prevent inter-chamber leakage.

Hi, I am working on wankel engine too. I tried imposing momentum source but it not working. Its always backflowing in the adjacent chamber. On the contrary when I am setting up a similar problem but only with translation not rotation then its working. Do you have any idea what it could be? Please let me know. I can also provide you udf which I wrote for marking the cells for momentum source.

Thanks in advance

Hi to all and apologies for reviving an old thread, hoping that the original posters will be notified by email.

I am trying to model the gas circuit in a Wankel engine, not combustion or anything, just the compression and expansion of the working gas.

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 written a Define CG macro UDF containing the x and y velocity equations found in texts but it seems smth is wrong.

Can you please give me some guidance?

Best regards,
Thanos

Hi Joe,

Could you please explain some details about the method of importing momentum source to sort the gap leakage problem?
I am an undergrad and quite new about CFD, although I have successfully modelled the operation.

Many thanks

Udf
 

Try to check initial CG position you have to give in fluent. Use this code it may help you

#include "udf.h"
#define r -0.0116 /*Eccentricity*/
#define k 57.2727 /*rad to degree*/
#define w 314.16 /*angular velocity in rad/sec*/

/* for grid motion */
DEFINE_CG_MOTION(rotor, dt, vel, omega,time, dtime)
{
real beta;

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;

}

Momentum sources
 

What I did was to mark the cells at rotor tip while it rotating and use DEFINE_SOURCE to make those marked cells a source which makes relative velocity between rotor tip and marked cells zero.

Thank you so much for the information. I am stuck here for months and so frustrated.

Did your model eventually work in terms of sealing the chamers?

Have you still got the SOURCE UDF file? Could you please post it?
I'm sure it will be very helpful for me.

Thank you very much. :)

It was working well when pressure difference around the seal was less but when pressure diff was increasing it started leaking again so I had to manipulate the coefficient in the source term to increase when pressure difference is increasing.
I have that file somewhere in my external hard disk. I'll look for it and let you know.

Hi Pravin,

Thanks a lot for your help.

I have another question here. How did you mark the cells around the tips in dynamic mesh(I tried yesterday while the marked cells became unmarked again after the rotor started rotating), Or did you change the orginal mesh to create new zones around the tips?
It'd be great and saving a lot of my time if you could please let me have a look at your case files. (My project is due in two weeks and my supervisor said, 'stop the leakage or fail'...:()

you will have to make a loop in udf using "begin_c_loop(c,t) / end_c_loop(c,t)" and mark them in each time step.

That makes a lot of sense. I'll try to go through relevant sections in the Fluent UDF manual and see if I can figure it, but still want to see your UDF.:)

Thanks for being so helpful. I appreciate it.

Hi Pravin,

How are you? I have been trying to figure out the way to import the momentum source, however, no progress. :(
I really really need your help. If possible, can I have your email address? I will be very grateful.
Thank you very much.

Actually port of my external is broken so I have to get it fixed only after tat I can send you momentum source file I wrote. By thet way I have one when it started working so I'll send you that one. my email address is pravin.gangwar@gmail.com

Thanks for the reply. I have sent you an email, please have a look.

how to use udf set the seal in the engine wankel please