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Gimlas January 16, 2012 15:02

Multiphase and different wall function approaches
 
Hello,
Iíve got a problem with a multiphase simulation in Fluent (Ansys Workbench 13). Iím trying to model a baffled cylindrical tank equipped with Rushton turbine. It is filled with a chalk particles suspended in water.
Firstly I have prepared a single phase simulation. Iíve used two approaches of k-e model: 1) scalable wall functions, 2) enhanced wall treatment. In the first case tetrahedrons mesh consisted of app. 1 000 000 of elements (orthogonal quality above 0.2). In the second case an inflation layer consisting of 10 sublayers was created (2 000 000 elements, orthogonal quality above 0.15). These simulations went well. My problems appeared when the multiphase model was activated. I cannot achieve satisfactory convergence. I have the following questions:

1) When enhanced wall treatment approach was chosen the first inflation layer thickness was equal to 1e-5m (in order to preserve y+<5) whereas the size of particles was equal to 1e-4m. According to my knowledge the element size has to be larger than the particles which flow through it. How to overcome this problem?

2) When scalable wall functions were used I could not trace the value of y* ( Ystar) of the walls. Y+ values where only available. Why?

Thank you for your help.

Best regards

RodriguezFatz July 5, 2012 09:10

Hi, I am facing exactly the same problem. Did you solve your question 1) ?

Kanarya April 5, 2013 07:45

Hi did you find the answer for it?
thanks
Quote:

Originally Posted by Gimlas (Post 339578)
Hello,
Iíve got a problem with a multiphase simulation in Fluent (Ansys Workbench 13). Iím trying to model a baffled cylindrical tank equipped with Rushton turbine. It is filled with a chalk particles suspended in water.
Firstly I have prepared a single phase simulation. Iíve used two approaches of k-e model: 1) scalable wall functions, 2) enhanced wall treatment. In the first case tetrahedrons mesh consisted of app. 1 000 000 of elements (orthogonal quality above 0.2). In the second case an inflation layer consisting of 10 sublayers was created (2 000 000 elements, orthogonal quality above 0.15). These simulations went well. My problems appeared when the multiphase model was activated. I cannot achieve satisfactory convergence. I have the following questions:

1) When enhanced wall treatment approach was chosen the first inflation layer thickness was equal to 1e-5m (in order to preserve y+<5) whereas the size of particles was equal to 1e-4m. According to my knowledge the element size has to be larger than the particles which flow through it. How to overcome this problem?

2) When scalable wall functions were used I could not trace the value of y* ( Ystar) of the walls. Y+ values where only available. Why?

Thank you for your help.

Best regards



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