Why do particle jump during CFD-DEM simulation?

Fatemeh Hosseini_22198

Hello, everybody,

I noticed particles jumping from the bottom of the tube during the CFD-DEM simulation (in a horizontal tube with gravity in the Z direction).
Since I have gravity in my system, they should move on the lower part of the tube. (Please refer to the attached)
I ran this simulation in a larger tube, and I didn't observe any strange behavior. Do you believe dp/D may be causing the problem? (D is the tube diameter, and dp is the particle diameter).
Currently, the D/dp is 200, whereas it was 1000 in the previous instance.
Or do you think the P-W surface energy is the cause of it? 


I appreciate your assistance in advance.

Regards,
Fatemeh

Prasad Avilala_20558

Hi Fatemeh,

 

The only reason I feel is the time step either in EDEM or CFD is larger.

You can try to reduce the time step in EDEM to lower until you get stable behavior or you can retain the current time step as it is in EDEM and reduce in CFD.

either way, it works.

 

Thanks,

Prasad A

Fatemeh Hosseini_22198

Prasad Avilala_20558 said:

Hi Fatemeh,

 

The only reason I feel is the time step either in EDEM or CFD is larger.

You can try to reduce the time step in EDEM to lower until you get stable behavior or you can retain the current time step as it is in EDEM and reduce in CFD.

either way, it works.

 

Thanks,

Prasad A

Thanks for your answer, Prasad.

In the last simulation CFD/DEM time step =50 and now it is 20.
EDEM timestep is 20% Rayleigh too.

Particles velocity is in the range of Fluid velocity and I think now it is stable. 


Regards,
Fatemeh

Prasad Avilala_20558

yes, hopefully, but you have to check and reduce until stable flow occurs.

 

 

Thanks,

Prasad A

Fatemeh Hosseini_22198

Prasad Avilala_20558 said:

yes, hopefully, but you have to check and reduce until stable flow occurs.

 

 

Thanks,

Prasad A

Dear Prasad,
I reduced the time step in the DEM section from 20% of Reyleigh to 15%, but nothing changed.
I also lowered the CFD time step, but the procedure wasn't made better. I still have the particles that jump.
I think it might be due to the D/dp or p-w surface energy.


Regards,
Fatemeh

Prasad Avilala_20558

Fatemeh Hosseini_22198 said:

Dear Prasad,
I reduced the time step in the DEM section from 20% of Reyleigh to 15%, but nothing changed.
I also lowered the CFD time step, but the procedure wasn't made better. I still have the particles that jump.
I think it might be due to the D/dp or p-w surface energy.


Regards,
Fatemeh

Hi Fatemeh,

are you using HWCFD (Acusolve)?

if yes, you can share the files let me take about the factory definition along with time step.

 

Thanks,

Prasad A

Fatemeh Hosseini_22198

Prasad Avilala_20558 said:

Hi Fatemeh,

are you using HWCFD (Acusolve)?

if yes, you can share the files let me take about the factory definition along with time step.

 

Thanks,

Prasad A

Thanks a lot
The file has been sent to your email.


Regards,
Fatemeh

Fatemeh Hosseini_22198

@Stephen Cole,  May I have your opinion too?

Thanks in advance.

Regards,
Fatemeh

Mahdi_22303

Is it possible that although you have reduced the size of the tube, you have increased the flow velocity to maintain a fixed discharge in the tube? Then, it is possible that sediment particles settle and then entrain into the flow by some sweeping and ejection motions. It might be a hydrodynamic reason.

Fatemeh Hosseini_22198

Mahdi_22303 said:

Is it possible that although you have reduced the size of the tube, you have increased the flow velocity to maintain a fixed discharge in the tube? Then, it is possible that sediment particles settle and then entrain into the flow by some sweeping and ejection motions. It might be a hydrodynamic reason.

Thanks for your comment, Mahdi.
Yes, I increased velocity from 3 to 14m/s.
I think it might be hydrodynamic issues as well.
I will run the simulation with a lower velocity to see the difference.
I checked the lower timestep/lower surface energy but they didn't change the results. 


Regards,
Fatemeh