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-   -   Help to plot variation of absolute pressure Vs time in transient problem (https://www.cfd-online.com/Forums/fluent/100144-help-plot-variation-absolute-pressure-vs-time-transient-problem.html)

Chirag2302 April 21, 2012 07:04

Help to plot variation of absolute pressure Vs time in transient problem
 
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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???????:confused:


Thanks......

banty April 21, 2012 17:27

U are getting constant pressure (101325 Pa) but the graph looks strange. should be parallel to time axis ?

LuckyTran April 21, 2012 17:41

Quote:

Originally Posted by Chirag2302 (Post 355968)
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???????:confused:


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.

Chirag2302 April 21, 2012 23:54

Thanks
 
Quote:

Originally Posted by banty (Post 356104)
U are getting constant pressure (101325 Pa) but the graph looks strange. should be parallel to time axis ?

Thank you....Banty

Chirag2302 April 22, 2012 00:01

Quote:

Originally Posted by LuckyTran (Post 356109)
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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