Spanwise/streamwise averaging in FLUENT/CFD Post?

orangesky · October 16, 2015, 14:00

Hi all,

I've done my simulations and am looking to plot the results. One of the things I would like to plot is my variable in a streamwise or spanwise location along the plane. I haven't been able to find a suitable solution so far.

The idea is to basically create a line, but instead of averaging (e.g. temperature) along that line, I would average all the values across it then plot the result on a graph.

Below is an example, except that I don't want to make so many lines. Would appreciate any ideas on how to proceed, thank you!

orangesky · October 28, 2015, 11:11

In case anyone else encounters a similar problem, here's what I've done so far.

I've resolved the issue by basically scripting the generation of a large number of lines, about 400 in my case for a 1.5m length surface.

I used the Record Session tool in CFD post to generate 1 line, then opened the session file. I took that into Excel and expanded it to 400 separate lines (used Excel to automatically change the location of each line).

I then took all that and put it back into Command Editor in CFD Post to generate all my lines. I then had to generate a lengthave variable linked to the expression I needed in my case (heat flux) for each line by using the same method as above, got 400 average values and then simply exported them all out to plot.

I feel like there should be a simple command to be able to average ACROSS a line rather than along it but this is the only solution I have so far. If anyone else has an idea, I would love to learn so do chip in! Cheers

LuckyTran · October 28, 2015, 11:28

I don't think there is an easier way to do it. Maybe it would be useful to implement as a utility but anyone that attempts this problem would end up generating many lines/planes similar to how you did it.

The problem is that you cannot define, in general, an average across a curve because the the path "across the curve" is not defined. Sure we implicitly understand that we are trying to plot streamwise and spanwise averages along a particular coordinate but a general purpose software should only need to handle a general case and not worry about particular geometry. It gets more complicated for example with flow in pipes or annulus where you want to take azimuthal averages. A typical flow scenario is very different for different users. It is best to have the curve explicitly specified by the user at the expense of some convenience.

orangesky · October 29, 2015, 12:40

Sure, but I figured it's something many people are likely to need and there may be a particular utility for it.

Especially with non-flat surfaces, it'd be difficult to do what I did in my case. I could see it being used in pipes for example to look at changes in a given number of planes along a line through the pipe.

CFD Post lines already require the user to define the number of samples so I thought there may be a way to link those samples to a plane/line-averaged value but...!

Thanks for your input

raghulvr · November 2, 2015, 09:11

I recommend you to try the same problem in CFX.Because in CFX,you can define expressions which make easier to compute the average value of some parameter in a particular domain
For example if you want to calculate average velocity at the outlet,you can define it as "areaave(velocity)@REGION:OUTLET"

October 16, 2015, 14:00	Spanwise/streamwise averaging in FLUENT/CFD Post?	#1
orangesky New Member Join Date: Mar 2014 Posts: 7 Rep Power: 12	Hi all, I've done my simulations and am looking to plot the results. One of the things I would like to plot is my variable in a streamwise or spanwise location along the plane. I haven't been able to find a suitable solution so far. The idea is to basically create a line, but instead of averaging (e.g. temperature) along that line, I would average all the values across it then plot the result on a graph. Below is an example, except that I don't want to make so many lines. Would appreciate any ideas on how to proceed, thank you!

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October 28, 2015, 11:11		#2
orangesky New Member Join Date: Mar 2014 Posts: 7 Rep Power: 12	In case anyone else encounters a similar problem, here's what I've done so far. I've resolved the issue by basically scripting the generation of a large number of lines, about 400 in my case for a 1.5m length surface. I used the Record Session tool in CFD post to generate 1 line, then opened the session file. I took that into Excel and expanded it to 400 separate lines (used Excel to automatically change the location of each line). I then took all that and put it back into Command Editor in CFD Post to generate all my lines. I then had to generate a lengthave variable linked to the expression I needed in my case (heat flux) for each line by using the same method as above, got 400 average values and then simply exported them all out to plot. I feel like there should be a simple command to be able to average ACROSS a line rather than along it but this is the only solution I have so far. If anyone else has an idea, I would love to learn so do chip in! Cheers

October 28, 2015, 11:28		#3
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,676 Rep Power: 66	I don't think there is an easier way to do it. Maybe it would be useful to implement as a utility but anyone that attempts this problem would end up generating many lines/planes similar to how you did it. The problem is that you cannot define, in general, an average across a curve because the the path "across the curve" is not defined. Sure we implicitly understand that we are trying to plot streamwise and spanwise averages along a particular coordinate but a general purpose software should only need to handle a general case and not worry about particular geometry. It gets more complicated for example with flow in pipes or annulus where you want to take azimuthal averages. A typical flow scenario is very different for different users. It is best to have the curve explicitly specified by the user at the expense of some convenience.

October 29, 2015, 12:40		#4
orangesky New Member Join Date: Mar 2014 Posts: 7 Rep Power: 12	Sure, but I figured it's something many people are likely to need and there may be a particular utility for it. Especially with non-flat surfaces, it'd be difficult to do what I did in my case. I could see it being used in pipes for example to look at changes in a given number of planes along a line through the pipe. CFD Post lines already require the user to define the number of samples so I thought there may be a way to link those samples to a plane/line-averaged value but...! Thanks for your input

November 2, 2015, 09:11		#5
raghulvr Member Rahul Join Date: Sep 2015 Posts: 39 Rep Power: 10	I recommend you to try the same problem in CFX.Because in CFX,you can define expressions which make easier to compute the average value of some parameter in a particular domain For example if you want to calculate average velocity at the outlet,you can define it as "areaave(velocity)@REGION:OUTLET"