Is it possible to use Eulerrian-Eulerian with large bubble size

Tleja · January 15, 2018, 03:50

Hi everyone

I'm studying hydrodynamic in Bubble column. As i seen in Experiment, bubble size of 1-2 cm was discharged from nozzle. At the moment, i used Eulerian-Eulerian model for simulating bubble behavior with Fixing bubble size of 1cm (Secondary phase).

I can't simulate this bubble column. It shows divergence in 20 iterations of first time step. I found some information from ANSYS theory about the relation of mesh size and bubble size. Therefore, I changed bubble size in my simulation from 1 cm to 0.5 mm. The well convergence simulation was found. Experimentally, the flow behaviors of 1cm and 0.5 mm bubble size are completely different. I prefer to use bubble size of 1 cm for this simulation.

How can i do with simulating big bubble size in Bubble column?
I prefers to use Eulerian-Eulerian model.

Should i use Eulerian-Eulerian with Multi-fluid VOF???

Best Regard
Tleja

BlnPhoenix · January 16, 2018, 07:36

Hello,

can you please post the relation between mesh size and bubble size from ANSYS? I never found such a thing.

On your problem: You can try following things

- decrease mesh size, meaning increase avg. cell size

- decrease time step, you said your simulation crashed within 20 time steps, try a smaller time step size, since larger bubbles have higher rising velocity..

- try Underrelaxation, smaller time step is preferrable though

- try the Multifluid-VOF model BUT usually this is good when you have free surfaces involved

CeesH · March 5, 2018, 11:14

I don't think there is a fundamental problem, as the Euler-Euler model takes an ensemble average and does not contain any direct information considering the bubble size.

However, if your mesh size is much smaller than the smallest bubbles, VOF may be a more realistic way of modeling.

Tleja · March 6, 2018, 00:04

Dear BlnPhoenix and CeesH

Thank you for your reply.

Unfortunately, solid particle of algae also disperses in my liquid phase.

I dont think we can used VOF for this system because of the particle dispersion.

At the moment, i try to use Multi-fluid VOF to solve this problem with the manipulation of model parameter as BlnPhoenix recommendation.

Best Regard
Tleja

CeesH · March 6, 2018, 06:30

Please let me know how the multi-fluid VOF works for you; I don't think it's suitable for dispersed flows - acting liker regular Euler-Euler in the region with many bubbles, and acting like VOF at the free surface. But if it does, I'd be interested.

January 15, 2018, 03:50	Is it possible to use Eulerrian-Eulerian with large bubble size	#1
Tleja Member Tleja Join Date: Sep 2013 Posts: 40 Rep Power: 13	Hi everyone I'm studying hydrodynamic in Bubble column. As i seen in Experiment, bubble size of 1-2 cm was discharged from nozzle. At the moment, i used Eulerian-Eulerian model for simulating bubble behavior with Fixing bubble size of 1cm (Secondary phase). I can't simulate this bubble column. It shows divergence in 20 iterations of first time step. I found some information from ANSYS theory about the relation of mesh size and bubble size. Therefore, I changed bubble size in my simulation from 1 cm to 0.5 mm. The well convergence simulation was found. Experimentally, the flow behaviors of 1cm and 0.5 mm bubble size are completely different. I prefer to use bubble size of 1 cm for this simulation. How can i do with simulating big bubble size in Bubble column? I prefers to use Eulerian-Eulerian model. Should i use Eulerian-Eulerian with Multi-fluid VOF??? Best Regard Tleja

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January 16, 2018, 07:36		#2
BlnPhoenix Senior Member Join Date: Aug 2014 Location: Germany Posts: 292 Rep Power: 14	Hello, can you please post the relation between mesh size and bubble size from ANSYS? I never found such a thing. On your problem: You can try following things - decrease mesh size, meaning increase avg. cell size - decrease time step, you said your simulation crashed within 20 time steps, try a smaller time step size, since larger bubbles have higher rising velocity.. - try Underrelaxation, smaller time step is preferrable though - try the Multifluid-VOF model BUT usually this is good when you have free surfaces involved

March 5, 2018, 11:14		#3
CeesH Senior Member Cees Haringa Join Date: May 2013 Location: Delft Posts: 607 Rep Power: 0	I don't think there is a fundamental problem, as the Euler-Euler model takes an ensemble average and does not contain any direct information considering the bubble size. However, if your mesh size is much smaller than the smallest bubbles, VOF may be a more realistic way of modeling.

March 6, 2018, 00:04		#4
Tleja Member Tleja Join Date: Sep 2013 Posts: 40 Rep Power: 13	Dear BlnPhoenix and CeesH Thank you for your reply. Unfortunately, solid particle of algae also disperses in my liquid phase. I dont think we can used VOF for this system because of the particle dispersion. At the moment, i try to use Multi-fluid VOF to solve this problem with the manipulation of model parameter as BlnPhoenix recommendation. Best Regard Tleja

March 6, 2018, 06:30		#5
CeesH Senior Member Cees Haringa Join Date: May 2013 Location: Delft Posts: 607 Rep Power: 0	Please let me know how the multi-fluid VOF works for you; I don't think it's suitable for dispersed flows - acting liker regular Euler-Euler in the region with many bubbles, and acting like VOF at the free surface. But if it does, I'd be interested.