[user9]

I am trying to simulate air water non boiling slug flow in a 2d axisymetric domain. heat flux is also applied. basically i should use vof but due to computational expenses i am using eulerian model and mixture model. but i m facing the problem of convergence as well as slug flow is not forming.Screenshot (71).jpg.
my contours are contours of vf of air.jpg


can someone tell me whether i should use implicit/ explicit scheme for volume fraction.
what should be my backflow conditions in pressure outlet.
any further advise is welcomed.

thnks

[vinerm]

Different multiphase models cater to different regimes. For the slug flow, VOF has to be used. VOF is slightly more expensive than Mixture but way less than Eulerian. Actually, there is no difference between mixture and VOF as far as conservation equations are concerned or solution field is concerned. The difference lies in reconstruction of interface and determination of momentum exchange across interface. So, it would be recommended to use VOF and not mixture or Eulerian.

Explicit schemes are good if requirement is accurate prediction of interface shape or when models based on interface shape are needed to be included, such as surface tension model. Otherwise, you may use Implicit. You can also use Implicit VOF as steady-state, provided the system has a steady-state.

[user9]

Actually I was assigned the task of comparing my problem results with different models of fluent. In eulerian model what should be my secondary phase diameter . By default it takes 1e-05 m. What about wall adhesion. Should I consider it and what should be my contact angle for eulerian model

[vinerm]

As you might be aware, the interface is not resolved in Euler-Euler model, i.e., the solver requires users to specify the length scale. There are no guidelines for this, however, since the exchange coefficients are calculated on cell by cell basis, it is recommended to use length scale of the order of mesh. Default is just a number since something other than 0 has to be there. You have to provide the number appropriate for your case. Whether it is Euler-Euler or VOF, the contact angle does not change; it is a property of fluid-pair and solid surface and not affected by the model. So, you have to use contact angle that you would use if you were using VOF.

[user9]

Originally Posted by vinerm

As you might be aware, the interface is not resolved in Euler-Euler model, i.e., the solver requires users to specify the length scale. There are no guidelines for this, however, since the exchange coefficients are calculated on cell by cell basis, it is recommended to use length scale of the order of mesh. Default is just a number since something other than 0 has to be there. You have to provide the number appropriate for your case. Whether it is Euler-Euler or VOF, the contact angle does not change; it is a property of fluid-pair and solid surface and not affected by the model. So, you have to use contact angle that you would use if you were using VOF.

Thankyou vinerm