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How to plot Cp vs. Theta on a 3d Cylinder

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Old   September 22, 2013, 12:07
Default How to plot Cp vs. Theta on a 3d Cylinder
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George Davis
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Hey all!

This is my first post here. I'm a senior undergrad at the Naval Academy in Annapolis and have started some independent research with one of my professors, obviously involving CFD. I've been using this site for the last month or so once I started learning Fluent and it's been an incredible resource.

However, I'm still stumped on some things.

I've calculated a solution for a 3d cylinder in steady conditions at Re=10^6. Right now I'm trying to plot Cp vs. theta or static pressure vs. theta on the cylinder at the symmetry plane in the center but I can't figure out how. When I try to plot pressure vs. curve length, the xy plot window won't let me select "cylinder" (the named selection for the cylinder surface".

I've googled a lot and read through relevant parts of the manual and haven't found a solution. I'd appreciate any help you guys can offer. Thanks!
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Old   September 23, 2013, 08:08
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Are you using FLUENT to do that thing or CFDPost? If you are using CFDPost, you have to create a new curve where to plot the Cp variable. To do that first create a surface on the plae of symmetry of you cylinder. Then create a new polyline as the intersection of the ylinder and tha plane of symmetry. Now you can plot the Cp variable across the lenght of the polyline. But with that method you can't figure out where is the exact location of the independet variable. So i recomend you to split you geometry in two parts ('upper' and 'lower') and then plot Cp vs 'x' or 'y', depending on you coordinate system, and then export the data to a spreadsheet and correlate the 'x' or 'y' variable with the theta one. Regards
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Old   September 23, 2013, 10:05
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George Davis
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I'm using CFDPost.

Thanks, I'll give that a shot.

I spent some time yesterday trying to figure out how to export the data but was unsuccessful. Is there a way to create a table and so that I can copy/paste the data into matlab or excel?

- George
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Old   September 23, 2013, 13:29
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Yes, In File/Export/Export/..., you have to select the variables, location (lines, surfaces). With al the rest of the parameters, leave as default. I don't know if you know the csv format, but it is an ASCII file with values comma separated, that you can open with a spreadsheet
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Old   September 25, 2013, 03:25
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cfd post can do that for sure, just browse a bit through i'ts help file..
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Old   September 25, 2013, 07:32
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gfoam's solution worked. I was able to extract all the x and pressure data and then use an acos function to determine theta.

The report I'm trying to compare to plots the spanwise average pressure vs. theta and not just at the center of the cylinder, so now I'm trying to figure out how to do that.

Thanks!
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