Finding static pressure profile

Tanjina · February 22, 2015, 13:37

Hello,

I am doing a transient turbulent simple pipe simulation with fixed mass flow rate. I was just wondering, what Fluent gives as 'static pressure", is it real static gauge pressure or do I need to do some modification? Because from phase contour, I see there is a clear air zone and water zone, so at air portion, pressure should be zero, right ? But I am getting ~50 pascal.

I set operating pressure at atmospheric pressure (P=101325 Pa) and reference pressure location is at some point, which is always filled with air ( As fluent tutorial said).

Any suggestion will be highly appreciated.

Regards,
Tanjina

ghost82 · February 23, 2015, 08:48

Hi Tanjina,
Static pressure is what you call real static pressure.
Are you plotting the cell centered or nodes values?
Try to plot cell centered values.

pakk · February 23, 2015, 08:50

I don't know why the static pressure in your air should be 0 pascal... Why do you think that?

Tanjina · February 23, 2015, 10:27

Hello Ghost82,

I used "node values' from Contour--> Options. How can I get cell centered values? Whenever I deselect the "node values" I find little bit different values. Why is that ?

@Pakk,

Since I set the operating pressure at 101325 pa and when I defined the pressure outlet, I gave the gauge pressure =0 ( I think this represents the atmospheric pressure at outlet ) , that's why I think that I should get zero pressure at air zone or at least at outlet. Please correct me if my thinking is wrong.

Thanks to all.

Regards,
tanjina

ghost82 · February 23, 2015, 10:29

Quote:

Originally Posted by Tanjina

Hello Ghost82,

I used "node values' from Contour--> Options. How can I get cell centered values? Whenever I deselect the "node values" I find little bit different values. Why is that ?

To get cell centered values simply deselect node values. You have different values because node values are interpolated values, cell centered values are the calculated values at each cell center, without interpolation: what values do you get if you deselect node values?

Tanjina · February 23, 2015, 10:38

Using cell centered value I get value in -6.125 to 4.604 pa
and using node values I get -6.478 to 4.524 pa

Previously this 4 pa was 50 pa. But after 2 more sec simulation , it's now 4pa !

Is it time dependant that pressure at outlet? Shouldn't it be constant over time ?

ghost82 · February 23, 2015, 11:03

Did you check if your time steps are converged?

Tanjina · February 23, 2015, 11:06

Yup, within 5-6 iteration, my results converged. I am using time step 0.0035 sec. And simulation time is 13.8 sec.

ghost82 · February 23, 2015, 11:24

Quote:

Originally Posted by Tanjina

Using cell centered value I get value in -6.125 to 4.604 pa
and using node values I get -6.478 to 4.524 pa

Previously this 4 pa was 50 pa. But after 2 more sec simulation , it's now 4pa !

Is it time dependant that pressure at outlet? Shouldn't it be constant over time ?

Can you plot cell centered values of static pressure in a 2d plot (not contour) at outlet and check?

Tanjina · February 23, 2015, 11:41

Here it is -

Line -outlet is the line at outlet and Line-14 is the line from where water detached from the upper pipe wall.

ghost82 · February 23, 2015, 11:53

And where is line-outlet? is it the same line in boundary conditions where you set 0 gauge pressure? is it the vertical line on the right?
Which of the two series is the outlet?

Tanjina · February 23, 2015, 19:06

Sorry Ghost82, I should've used two color.

In this geometry, there is two zone ( Long rectangular) ..one is pipe and one is reservoir zone ( small rectangular). Hydrostatic line is the pressure at that point after that water surface detached from the pipe surface. And other line is pressure at end of pipe. And I set zero at the end of reservoir which is the right most line of contour plot and I defined that point as outlet.

From end of the pipe , all reservoir zone is patched with air.

February 22, 2015, 13:37	Finding static pressure profile	#1
Tanjina Senior Member Tanjina Afrin Join Date: May 2013 Location: South Carolina Posts: 169 Rep Power: 12	Hello, I am doing a transient turbulent simple pipe simulation with fixed mass flow rate. I was just wondering, what Fluent gives as 'static pressure", is it real static gauge pressure or do I need to do some modification? Because from phase contour, I see there is a clear air zone and water zone, so at air portion, pressure should be zero, right ? But I am getting ~50 pascal. I set operating pressure at atmospheric pressure (P=101325 Pa) and reference pressure location is at some point, which is always filled with air ( As fluent tutorial said). Any suggestion will be highly appreciated. Regards, Tanjina

February 23, 2015, 08:48		#2
ghost82 Senior Member Rick Join Date: Oct 2010 Posts: 1,016 Rep Power: 26	Hi Tanjina, Static pressure is what you call real static pressure. Are you plotting the cell centered or nodes values? Try to plot cell centered values. __________________ Google is your friend and the same for the search button!

February 23, 2015, 11:03		#7
ghost82 Senior Member Rick Join Date: Oct 2010 Posts: 1,016 Rep Power: 26	Did you check if your time steps are converged? __________________ Google is your friend and the same for the search button!

February 23, 2015, 11:53		#11
ghost82 Senior Member Rick Join Date: Oct 2010 Posts: 1,016 Rep Power: 26	And where is line-outlet? is it the same line in boundary conditions where you set 0 gauge pressure? is it the vertical line on the right? Which of the two series is the outlet? __________________ Google is your friend and the same for the search button!

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February 23, 2015, 08:50		#3
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 26	I don't know why the static pressure in your air should be 0 pascal... Why do you think that?

February 23, 2015, 10:27		#4
Tanjina Senior Member Tanjina Afrin Join Date: May 2013 Location: South Carolina Posts: 169 Rep Power: 12	Hello Ghost82, I used "node values' from Contour--> Options. How can I get cell centered values? Whenever I deselect the "node values" I find little bit different values. Why is that ? @Pakk, Since I set the operating pressure at 101325 pa and when I defined the pressure outlet, I gave the gauge pressure =0 ( I think this represents the atmospheric pressure at outlet ) , that's why I think that I should get zero pressure at air zone or at least at outlet. Please correct me if my thinking is wrong. Thanks to all. Regards, tanjina

February 23, 2015, 10:38		#6
Tanjina Senior Member Tanjina Afrin Join Date: May 2013 Location: South Carolina Posts: 169 Rep Power: 12	Using cell centered value I get value in -6.125 to 4.604 pa and using node values I get -6.478 to 4.524 pa Previously this 4 pa was 50 pa. But after 2 more sec simulation , it's now 4pa ! Is it time dependant that pressure at outlet? Shouldn't it be constant over time ?

February 23, 2015, 11:06		#8
Tanjina Senior Member Tanjina Afrin Join Date: May 2013 Location: South Carolina Posts: 169 Rep Power: 12	Yup, within 5-6 iteration, my results converged. I am using time step 0.0035 sec. And simulation time is 13.8 sec.

February 23, 2015, 19:06		#12
Tanjina Senior Member Tanjina Afrin Join Date: May 2013 Location: South Carolina Posts: 169 Rep Power: 12	Sorry Ghost82, I should've used two color. In this geometry, there is two zone ( Long rectangular) ..one is pipe and one is reservoir zone ( small rectangular). Hydrostatic line is the pressure at that point after that water surface detached from the pipe surface. And other line is pressure at end of pipe. And I set zero at the end of reservoir which is the right most line of contour plot and I defined that point as outlet. From end of the pipe , all reservoir zone is patched with air.