Total pressure boundary condition at inlet:how to sustain inlet pressure in cfx

faizan · March 10, 2014, 05:59

Hi All,

I have selected Total pressure of 1.4MPa at Inlet in ANSYS CFX software. I am modeling a Nitrogen gas flow through convergent-divergent DeLaval Nozzle. I set a areaAve(Pressure) monitor at inlet in solver control monitors. After 3 4 iterations the inlet monitor shows drastic drop of pressure form 1.4e6 Pa to 2e5Pa. How can I imposed a constant total pressure boundary condition at Inlet? Please help...

ghorrocks · March 10, 2014, 16:18

You imposed constant total pressure. You are monitoring pressure. The difference is the dynamic head. If your monitor on total pressure it should be your boundary value setting.

faizan · March 10, 2014, 22:52

Thanks ghorrock for your response.

Can you suggest me about the expression of total pressure monitor?

ghorrocks · March 11, 2014, 06:29

areaAve(Total Pressure)@inlet

Look in the CFX reference manual for a full list of available variables and their names.

faizan · March 15, 2014, 22:28

Thanks ghorrock,

I have solved the total pressure issue. But another problem occurred with total temperature. When I set the total temperature expression at inlet it is just showing a flat line at 0 value. The total temp at inlet is set to 550 deg C. Please see the attached picture and reply.

Thanks in advance.

ghorrocks · March 16, 2014, 04:37

Have you seen the y scale size? Maybe you should put the temperature curve on another plot with more appropriate scaling.....

faizan · March 17, 2014, 20:53

Thanks ghorrocks- I have separated the plots and now it is better.

Can you suggest that how can I put the pressure monitors on different locations over the length of nozzle. At the moment I put the monitor on inlet and it is showing. I need to check the pressure on throat section which is at 81.2 mm linear distance from inlet. Also one pressure monitor at exit of nozzle which is at 151.2 mm distance form the inlet.

How can I set the pressure monitor at these distances ? please suggest.I am CONFUSED...

ghorrocks · March 17, 2014, 22:44

Try a monitor point set at a specific XYZ location.

faizan · March 18, 2014, 04:06

This is the problem. I am unable to find from where and how can I set specific location at nozzle length.

I tried the option imprint but it is not showing and inactive in my model because my model geometry have frozen bodies.

Please suggest?

chiragsvnit · March 18, 2014, 06:27

Have you created monitoring points using XYZ values at CFX Pre during job set-up along with monitoring variables? The option is available in Monitoring Tab CFX Pre.

ghorrocks · March 18, 2014, 16:47

You do not set up monitor points in the meshing. You set it up in CFX-Pre.

March 10, 2014, 05:59	Total pressure boundary condition at inlet:how to sustain inlet pressure in cfx	#1
faizan New Member Join Date: Feb 2014 Posts: 21 Rep Power: 12	Hi All, I have selected Total pressure of 1.4MPa at Inlet in ANSYS CFX software. I am modeling a Nitrogen gas flow through convergent-divergent DeLaval Nozzle. I set a areaAve(Pressure) monitor at inlet in solver control monitors. After 3 4 iterations the inlet monitor shows drastic drop of pressure form 1.4e6 Pa to 2e5Pa. How can I imposed a constant total pressure boundary condition at Inlet? Please help...

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March 10, 2014, 16:18		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	You imposed constant total pressure. You are monitoring pressure. The difference is the dynamic head. If your monitor on total pressure it should be your boundary value setting.

March 10, 2014, 22:52		#3
faizan New Member Join Date: Feb 2014 Posts: 21 Rep Power: 12	Thanks ghorrock for your response. Can you suggest me about the expression of total pressure monitor?

March 11, 2014, 06:29		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	areaAve(Total Pressure)@inlet Look in the CFX reference manual for a full list of available variables and their names.

March 16, 2014, 04:37		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Have you seen the y scale size? Maybe you should put the temperature curve on another plot with more appropriate scaling.....

March 17, 2014, 20:53		#7
faizan New Member Join Date: Feb 2014 Posts: 21 Rep Power: 12	Thanks ghorrocks- I have separated the plots and now it is better. Can you suggest that how can I put the pressure monitors on different locations over the length of nozzle. At the moment I put the monitor on inlet and it is showing. I need to check the pressure on throat section which is at 81.2 mm linear distance from inlet. Also one pressure monitor at exit of nozzle which is at 151.2 mm distance form the inlet. How can I set the pressure monitor at these distances ? please suggest.I am CONFUSED...

March 17, 2014, 22:44		#8
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Try a monitor point set at a specific XYZ location.

March 18, 2014, 04:06		#9
faizan New Member Join Date: Feb 2014 Posts: 21 Rep Power: 12	This is the problem. I am unable to find from where and how can I set specific location at nozzle length. I tried the option imprint but it is not showing and inactive in my model because my model geometry have frozen bodies. Please suggest?

March 18, 2014, 06:27		#10
chiragsvnit New Member Chirag Trivedi Join Date: Sep 2009 Location: Norway Posts: 26 Rep Power: 16	Have you created monitoring points using XYZ values at CFX Pre during job set-up along with monitoring variables? The option is available in Monitoring Tab CFX Pre.

March 18, 2014, 16:47		#11
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	You do not set up monitor points in the meshing. You set it up in CFX-Pre.