Multiphase simulation in FLUENT for rotating equipment

joshghoun · October 18, 2014, 07:57

I am trying to model an predict the NPSHR in centrifugal pumps I wonder that is there any special model or way of defining boundaries for reaching some reasonable results.

swiftaircraft · October 21, 2014, 02:46

There is no special way for this case. Just make sure that the grid resolution is fine enough to provide decent pressure profiles. The difference between the inlet pressure and the lowest pressure in the domain, in combination with knowing the vapour pressure of the liquid, should be sufficient to define the NPSHR.

joshghoun · October 21, 2014, 07:20

I wonder if there is a model for visualization of vapor which are produced in cavitation phenomena...
Thanks for your answers

swiftaircraft · October 21, 2014, 07:30

There is a built in cavitation model within Fluent that you can use. You need to run a multiphase simulation but it will show vapour generation should you go below the vapour pressure.

joshghoun · October 21, 2014, 07:55

Yes you are right, but I have tried some mutliphase models the run doesn't start...
If it is possible for you help me about the settings for simulating cavitation visualization in FLUENT for Centrifugal Pumps.

swiftaircraft · October 21, 2014, 08:10

Please refer to http://www.docin.com/p-392460303.html

joshghoun · October 21, 2014, 08:39

It is vary nice & helpful tutorial...
I am going to study and let you know the results.

ghost82 · October 21, 2014, 08:44

Hi!
If you want to evaluate NPSHr, why you want to simulate cavitation?
Pump must avoid cavitation during operation and so NPSHr is well above this limits.
I think you should run single phase simulations: if you see absolute pressure <= vapor pressure, it's not realistic (in your case): this means that in these areas cavitation occurs, so you need to change boundary conditions to avoid it.
Moreover, simulation of cavitation si not straightforward: all the models are "incompleted", as the terms in the source equations don't take into account all the members of the Rayleight equation, and this, in some cases, lead to converged solutions, but irrealistic results.
Custom cavitation models can be implemented through udfs, but they require fine tuning with experimental data.

Daniele

October 18, 2014, 07:57	Multiphase simulation in FLUENT for rotating equipment	#1
joshghoun New Member Azarbayjan-e Sharqi (East Azerbaijan) Join Date: May 2014 Posts: 9 Rep Power: 11	I am trying to model an predict the NPSHR in centrifugal pumps I wonder that is there any special model or way of defining boundaries for reaching some reasonable results.

October 21, 2014, 02:46		#2
swiftaircraft Member David Stanbridge Join Date: Apr 2010 Location: Norwich, UK Posts: 59 Rep Power: 16	There is no special way for this case. Just make sure that the grid resolution is fine enough to provide decent pressure profiles. The difference between the inlet pressure and the lowest pressure in the domain, in combination with knowing the vapour pressure of the liquid, should be sufficient to define the NPSHR. __________________ David Stanbridge Swift TG Solutions Limited www.swifttgsolutions.com

October 21, 2014, 07:20	Thanks dear David	#3
joshghoun New Member Azarbayjan-e Sharqi (East Azerbaijan) Join Date: May 2014 Posts: 9 Rep Power: 11	I wonder if there is a model for visualization of vapor which are produced in cavitation phenomena... Thanks for your answers

October 21, 2014, 07:30		#4
swiftaircraft Member David Stanbridge Join Date: Apr 2010 Location: Norwich, UK Posts: 59 Rep Power: 16	There is a built in cavitation model within Fluent that you can use. You need to run a multiphase simulation but it will show vapour generation should you go below the vapour pressure. __________________ David Stanbridge Swift TG Solutions Limited www.swifttgsolutions.com

October 21, 2014, 07:55	Thanks dear David	#5
joshghoun New Member Azarbayjan-e Sharqi (East Azerbaijan) Join Date: May 2014 Posts: 9 Rep Power: 11	Yes you are right, but I have tried some mutliphase models the run doesn't start... If it is possible for you help me about the settings for simulating cavitation visualization in FLUENT for Centrifugal Pumps.

October 21, 2014, 08:10		#6
swiftaircraft Member David Stanbridge Join Date: Apr 2010 Location: Norwich, UK Posts: 59 Rep Power: 16	Please refer to http://www.docin.com/p-392460303.html joshghoun likes this. __________________ David Stanbridge Swift TG Solutions Limited www.swifttgsolutions.com

October 21, 2014, 08:39	Thanks David	#7
joshghoun New Member Azarbayjan-e Sharqi (East Azerbaijan) Join Date: May 2014 Posts: 9 Rep Power: 11	It is vary nice & helpful tutorial... I am going to study and let you know the results.

October 21, 2014, 08:44		#8
ghost82 Senior Member Rick Join Date: Oct 2010 Posts: 1,016 Rep Power: 26	Hi! If you want to evaluate NPSHr, why you want to simulate cavitation? Pump must avoid cavitation during operation and so NPSHr is well above this limits. I think you should run single phase simulations: if you see absolute pressure <= vapor pressure, it's not realistic (in your case): this means that in these areas cavitation occurs, so you need to change boundary conditions to avoid it. Moreover, simulation of cavitation si not straightforward: all the models are "incompleted", as the terms in the source equations don't take into account all the members of the Rayleight equation, and this, in some cases, lead to converged solutions, but irrealistic results. Custom cavitation models can be implemented through udfs, but they require fine tuning with experimental data. Daniele joshghoun likes this.

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