# Help to plot variation of absolute pressure Vs time in transient problem

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April 21, 2012, 07:04
Help to plot variation of absolute pressure Vs time in transient problem
#1
New Member

Chirag
Join Date: Feb 2012
Posts: 18
Rep Power: 6
Hello,

I am analyzing a oscillatory flow in channel. I am using 2D,Pressure based solver, Transient model. I want output at a one point.

I had defined a surface monitor at that particular point for Area weighted absolute pressure Vs flow time....I think it is right but my output is as shown in fig.

Can anyone help me to correct this???????

Thanks......
Attached Images
 Absolute pressure Vs time at point after stack.jpg (81.9 KB, 30 views)

 April 21, 2012, 17:27 #2 Member   banty Join Date: Mar 2012 Posts: 52 Rep Power: 6 U are getting constant pressure (101325 Pa) but the graph looks strange. should be parallel to time axis ?

April 21, 2012, 17:41
#3
Senior Member

Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 1,334
Rep Power: 20
Quote:
 Originally Posted by Chirag2302 Hello, I am analyzing a oscillatory flow in channel. I am using 2D,Pressure based solver, Transient model. I want output at a one point. I had defined a surface monitor at that particular point for Area weighted absolute pressure Vs flow time....I think it is right but my output is as shown in fig. Can anyone help me to correct this??????? Thanks......
Use one of the two: vertex minimum, or maximum. Do not use vertex average, and also do not any of the weighted averages. If you use vertex minimum/maximum it will simply output the min/max of all values. If your monitor is a single point it will output only that point. If you use one of the weighted averages it will start to compute the quantities (and introduce small errors, such as the vertex area). It is simply better to use one of the vertex options.

Other than that, it seems (at least your plot) is outputting correctly. If it was a transient simulation I would expect stronger pressure oscillations, but it seems your pressure is fairly constant with small oscillations (these are probably introduced by the averaging scheme). You are also plotting against time-step so it may be hard to judge.

April 21, 2012, 23:54
Thanks
#4
New Member

Chirag
Join Date: Feb 2012
Posts: 18
Rep Power: 6
Quote:
 Originally Posted by banty U are getting constant pressure (101325 Pa) but the graph looks strange. should be parallel to time axis ?
Thank you....Banty

April 22, 2012, 00:01
#5
New Member

Chirag
Join Date: Feb 2012
Posts: 18
Rep Power: 6
Quote:
 Originally Posted by LuckyTran Use one of the two: vertex minimum, or maximum. Do not use vertex average, and also do not any of the weighted averages. If you use vertex minimum/maximum it will simply output the min/max of all values. If your monitor is a single point it will output only that point. If you use one of the weighted averages it will start to compute the quantities (and introduce small errors, such as the vertex area). It is simply better to use one of the vertex options. Other than that, it seems (at least your plot) is outputting correctly. If it was a transient simulation I would expect stronger pressure oscillations, but it seems your pressure is fairly constant with small oscillations (these are probably introduced by the averaging scheme). You are also plotting against time-step so it may be hard to judge.
Thank you.......LuckyTran

I had also monitored with respect to flow time but the output is same. and you are right strong pressure oscillation is expected with amplitude approximately near to 7500 to 8500 Pascals with oscillation frequency of 614 Hz.

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