wrong void fraction at the inlet boundary

Submitted by gelinhan on Mon, 01/23/2017 - 11:17

Hi there,

I am now using CFDEM to simulate a simple liquid-solid fluidized bed with a void fraction of 0.53. I used the divided void fraction model. However, the void fraction close to the inlet I got were close to 1 which caused the bottom particles staying nearly still. Please kindly find attached the image of the void fraction.

I also ran the tutorial ErgunTestMPI but setting the inlet velocity just above the minimum fluidizing velocity to check the bottom particles motion. Unfortunately, I got the same phenomenon that bottom particles were almost stationary. The most likely reason I guess is due to the voidfraction set at the inlet is 1 that affecting the nearby cell values of void fraction (interpolation?). Can you please tell me how to solve this problem or is there anything I ignored?

Thank you.
Linhan

AttachmentSize
Image icon voidfraction.jpg31.77 KB

Forums:

gelinhan | Mon, 01/23/2017 - 22:41

Sorry guys, the wrong void fraction is because of the interpolation in the paraview. When I change the colouring method in the paraview, it goes well. But still, the bottom particles didn't move around.

cgoniva's picture

cgoniva | Tue, 01/24/2017 - 10:22

Hi Linhan,

you can try: using zero gradient for voidfraction at the inlet.

But keep an eye at the fluid flow rate. As U is the interstitial velocity, the particles will affect the superficial velocity (voidfraction*U).

Alternatively try not having the particles close to the flow inlet?

Alternatively write a new boundary condition accounting for the voidfraction and keeping the superficial velocity constant.

Best regards,

Christoph

gelinhan | Tue, 01/24/2017 - 11:32

Hi Christoph,

Much appreciated for your advice. I will try those methods and give feedback later.

Kind regards,

Linhan