tut "Drop curve for cavitating Flow in the Pump"

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 June 22, 2012, 23:28 tut "Drop curve for cavitating Flow in the Pump" #1 Member   leo Join Date: Jun 2012 Posts: 98 Rep Power: 6 Today i have done the tutorial "Drop curve for cavitating Flow in the Pump". Because the cavitation is taken into consideration, it is a multiphase problem. In the domain settings, the homogeneous model is selected. The documentation explain"The homogeneous model is selected because the interphase rate is large in the pump.This results in all fluids sharing a common flow field and turbulence." I do not get it. can someone explain to me ? Thank you. And whether the free surface model should be used? Leo

 June 23, 2012, 06:29 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,715 Rep Power: 99 One of the tutorial examples does a cavitating flow. Have a look at it for how to set up cavitation. Homogeneous means that the different phases shaer a variable field, for instance velocity. If the velocity field is homogeneous then the two phases share the same velocity fields. The alternative is that each phase has its own velocity field and they interact with interphase slip on the differential velocity.

 June 23, 2012, 10:03 #3 Member   leo Join Date: Jun 2012 Posts: 98 Rep Power: 6 Glenn,thank you for your reply, As my understanding, the homogeneous model is used under two conditions. 1)the phases are clearly stratified. 2)the drag dominated the flow with the absence of body force.eg.tiny particle in continuous phase. The essence of the homogeneous model is the the transported quantities are shared,so,only one set of the PDES are needed ,that makes great simplification.

 June 23, 2012, 10:18 #4 Member   leo Join Date: Jun 2012 Posts: 98 Rep Power: 6 1)Glenn ,if we want to solve the control equations of the homogeneous model.We need additional control equation which controls the volume fraction.Right?How to set up that equation? 2)And the homogeneous model is always used with the free surface model.How to handle transition area?Is the homogeneous model is suitable for that area,if there is significant slip? 3)why need the free surface model as all the transported quantities can be given by the homogeneous model.what is free surface for?

 June 24, 2012, 07:18 #5 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,715 Rep Power: 99 1) Several tutorial examples use multiphase modelling, some with free surface models. Have a look how they set it up. 2) No, homogeneous model can be used in either free surface or zero interphase slip flows, as your previous post says. What transition area are you referring to? 3) Do the tutorials and things will become clearer.

 June 24, 2012, 22:54 #6 Member   leo Join Date: Jun 2012 Posts: 98 Rep Power: 6 Thank you,i will turn to tutorial for help. Last question, if two phases are stratified.eg：air is above the water,open channel flow. Does there exist a interphase slip between the phases? As the knowledge learned from the fluid dynamics,no slip right.right?So homogeneous +free surface is available. Homogeneous model for shared variable field. free surface model for to capture good interface shape feature.

 June 24, 2012, 22:58 #7 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,715 Rep Power: 99 That is the usual approach. But have a look at the tutorial for the normal setup of a cavitating flow.

June 24, 2012, 23:02
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leo
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Quote:
 Originally Posted by ghorrocks That is the usual approach. But have a look at the tutorial for the normal setup of a cavitating flow.
Thank you sincerely

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