[karahan]

Hello People,

I have difficulties understanding the definition of the mass flow inlet boundary condition by Eulerian Multiphase Model in StarCCM+. I have two phases, both liquids with constant density. If I define a mass flow inlet, then I am required to define the mass flow rates and volume fractions of both phases seperately. But if the phases have constant density, why do I have to define the volume fraction of each phase additionally? It can be calculated from the mass flow rate and density.

It should not be possible to define a non-zero mass flow rate for a certain phase and a zero volume fraction for that phase at the same time or vice versa.

In the VOF-Model for example, you define a common mass flow inlet for both phases and specify the volume fractions of each phase. In this case, there is no overdetermination, in my opinion.

Please enlighten me if you can and thanks a lot.

[ping]

vof is a simpler multi-phase physics whereas emp is much more sophisticated and allows great flexibility on the number and types of phases and so this is why the menus are setup to give you those options

[karahan]

Originally Posted by ping

vof is a simpler multi-phase physics whereas emp is much more sophisticated and allows great flexibility on the number and types of phases and so this is why the menus are setup to give you those options

Your answer does not help. It is a very general answer without regard to the specific question above. You can just copy paste irrelevant information from the user hand book. It is already clear EMP is more complex and gives you more options. This has nothing to do with my question regarding the overdetermination at the user inlet.

Better skip questions then lowering the quality of the forum.

[karahan]

I am still looking for an answer for the question. Thanks...

[ping]

Well after an ungracious reply to my answer you can hardly expect others to answer. If you are prepared to humbly lower yourself a little and accept that some users need initial general answers, then I will give you an example of why that feature is very necessary for more advanced usage of this wonderful software.

[karahan]

I did not want to be arrogant. I just could not relate your general answer to my specific question. If the answers and questions are more specific, well described, it would lead to a certain quality in the forum. That is what I meant. Please do not take it personally.

I know in VOF-Model there is only one set of transport equations and a scalar equation for the volume fraction. The phases can't have different velocities. Whereas in the EMP there are two set of transport equations, which means a seperate velocity field for both phases. I don't understand how this justifies the definition of Volume Fraction in addition to Mass Flow Rate, where the density is a known variable.

I would be very glad, if you have an answer. My bitter answer above was for sure not a friendly one.

[ping]

I imagine there are several reason why the menus are setup this way and a very useful example that I have used is when the phases are stratified in a one or more properties such as mass flow and volume fraction which can be achieved using field functions, table input etc

[karahan]

Thank you for your answer. Can you please tell me more in detail, why you had to define mass flow rate as well as the volume fraction of the both phases seperately? Did you have to calculate the volume fraction from the mass flow rate and density by yourself? If so, it does not seem right to me, because what you can calculate, can solver as well, if the density is a known quantity.

I would be glad, if someone can refute this.

[ping]

sorry i've been away. it was many years ago when i used that feature so can't remember any detail.