mass averaged pressure and area averaged pressure

soni_sth · February 9, 2012, 18:18

I have static pressure data at outlet of turbine from experiment.HOw do we calculate mass averaged or area averaged pressure for outlet BC in cfx?

I really need help on this!!!!!!

Darren Leong · February 9, 2012, 20:28

CFX post
* using 'Outlet' as an example of the bc name

Create a table in 'Table Viewer' and use the following expression:
areaAve(Pressure)@Outlet

or

Use function calculator:
Function - areaAve
Location - Outlet
Variable - Pressure
Direction - None (set to global if you want to check in x,y,z direction)

soni_sth · February 12, 2012, 21:41

Thanks Darren.It gave the Area Avg static pressure at the outlet.But the value of torque didn't change.Shouldn't CFX recalculate the values once we change static pressure into area average??

Also,How do we plot performance curve of a turbine.For example if we have to plot RPM Vs Power,do we have to run lot of simulations to plot the curve?
Also,How do we address cavitation in the simulation?

I really need a help!!

ghorrocks · February 13, 2012, 07:21

These are all post processing activities, so of course the torque did not change. Why did you expect it to change?

Read the documentation on the best practices guide for turbomachinery.

Cavitation - Do the tutorial on cavitation. But based on your questions I suspect you are new to CFD and I would recommend you not do cavitation modelling until you understand some of the basics. Cavitation modelling is very tricky to get working properly.

soni_sth · February 13, 2012, 16:50

Thanks Glenn.I will do teh cavitation tutorials.But one question:In which cases do we model cavitation?Do we have to do in all teh cases?My values from CFD is not matching with EFD.I have not used cavitation model.SO can this be the reason?help me out Please.If you need more information plz ask me.I am stuck!!

ghorrocks · February 13, 2012, 17:24

If you don't even know when cavitation could be an issue then definitely do not use it. I repeat my previous comment - forget about cavitation modelling until you have a wider CFD experience.

What is EFD?

If your simulations are not accurate then try this FAQ: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

soni_sth · February 14, 2012, 13:41

Thanks for the reply Glenn!My professor told me not to do with cavitation.I am using Experimental data.I have pressure at inlet,outlet,RPM and mass flow rate.I want to develop the performance curve of a turbine and validate with the experimental results.I used total pressure at inlet and static outlet pressure and used same RPM values of the experiment but my POwer Vs RPM curve does not follow the trend.As we increase the RPM,power increases and then decreases for a constant head.

Can you suggest me.

ghorrocks · February 14, 2012, 17:37

I have already made two suggestions:

Quote:

Read the documentation on the best practices guide for turbomachinery

and

Quote:

If your simulations are not accurate then try this FAQ: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

February 9, 2012, 18:18	mass averaged pressure and area averaged pressure	#1
soni_sth New Member soni Join Date: Oct 2011 Posts: 25 Rep Power: 15	I have static pressure data at outlet of turbine from experiment.HOw do we calculate mass averaged or area averaged pressure for outlet BC in cfx? I really need help on this!!!!!!

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February 9, 2012, 20:28		#2
Darren Leong Member Darren Leong Join Date: Dec 2010 Posts: 64 Rep Power: 16	CFX post * using 'Outlet' as an example of the bc name Create a table in 'Table Viewer' and use the following expression: areaAve(Pressure)@Outlet or Use function calculator: Function - areaAve Location - Outlet Variable - Pressure Direction - None (set to global if you want to check in x,y,z direction)

February 12, 2012, 21:41		#3
soni_sth New Member soni Join Date: Oct 2011 Posts: 25 Rep Power: 15	Thanks Darren.It gave the Area Avg static pressure at the outlet.But the value of torque didn't change.Shouldn't CFX recalculate the values once we change static pressure into area average?? Also,How do we plot performance curve of a turbine.For example if we have to plot RPM Vs Power,do we have to run lot of simulations to plot the curve? Also,How do we address cavitation in the simulation? I really need a help!!

February 13, 2012, 07:21		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	These are all post processing activities, so of course the torque did not change. Why did you expect it to change? Read the documentation on the best practices guide for turbomachinery. Cavitation - Do the tutorial on cavitation. But based on your questions I suspect you are new to CFD and I would recommend you not do cavitation modelling until you understand some of the basics. Cavitation modelling is very tricky to get working properly.

February 13, 2012, 16:50		#5
soni_sth New Member soni Join Date: Oct 2011 Posts: 25 Rep Power: 15	Thanks Glenn.I will do teh cavitation tutorials.But one question:In which cases do we model cavitation?Do we have to do in all teh cases?My values from CFD is not matching with EFD.I have not used cavitation model.SO can this be the reason?help me out Please.If you need more information plz ask me.I am stuck!!

February 13, 2012, 17:24		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	If you don't even know when cavitation could be an issue then definitely do not use it. I repeat my previous comment - forget about cavitation modelling until you have a wider CFD experience. What is EFD? If your simulations are not accurate then try this FAQ: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

February 14, 2012, 13:41		#7
soni_sth New Member soni Join Date: Oct 2011 Posts: 25 Rep Power: 15	Thanks for the reply Glenn!My professor told me not to do with cavitation.I am using Experimental data.I have pressure at inlet,outlet,RPM and mass flow rate.I want to develop the performance curve of a turbine and validate with the experimental results.I used total pressure at inlet and static outlet pressure and used same RPM values of the experiment but my POwer Vs RPM curve does not follow the trend.As we increase the RPM,power increases and then decreases for a constant head. Can you suggest me.