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

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 September 22, 2013, 12:07 How to plot Cp vs. Theta on a 3d Cylinder #1 New Member   Join Date: Sep 2013 Posts: 3 Rep Power: 6 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!

 September 23, 2013, 08:08 #2 Senior Member   Gonzalo Join Date: Mar 2011 Location: Argentina Posts: 120 Rep Power: 9 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 Gonzalo Shubham_SD likes this.

 September 23, 2013, 10:05 #3 New Member   Join Date: Sep 2013 Posts: 3 Rep Power: 6 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

 September 23, 2013, 13:29 #4 Senior Member   Gonzalo Join Date: Mar 2011 Location: Argentina Posts: 120 Rep Power: 9 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

 September 25, 2013, 03:25 #5 Member     Join Date: Jul 2011 Posts: 74 Blog Entries: 1 Rep Power: 12 cfd post can do that for sure, just browse a bit through i'ts help file.. __________________ I'M NOT A GYNECOLOGIST BUT I'LL TAKE A LOOK.

 September 25, 2013, 07:32 #6 New Member   Join Date: Sep 2013 Posts: 3 Rep Power: 6 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!

 September 21, 2014, 13:33 #7 New Member   Kiran Kumar Reddy Join Date: Sep 2014 Posts: 2 Rep Power: 0 how to convert x-position to theta in excel

September 21, 2015, 05:27
#8
Member

N B Khan
Join Date: Jan 2014
Posts: 39
Rep Power: 6
Quote:
 Originally Posted by gfoam 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 Gonzalo
Sir i created the polyline and also draw the chart of Cp along the polyline,,, But i want to draw the chart of Cd Vs time, or Cl versus time... I can find the value of Cd,both in Fluent solver and Cfd post,but unable to plot the time history... Also want to make FFT versus time plot... please help me

 September 23, 2015, 17:41 #9 Senior Member   Gonzalo Join Date: Mar 2011 Location: Argentina Posts: 120 Rep Power: 9 Hi. If you are doing a transient simulation, you can plot the Cd, Cl and other force and moment coefficients as a function of time using the monitors in fluent. There are specific monitors of that coefficients in FLUENT and you can export them as chart in a ASCI file, everithing automatically with fluent. To do a FFT of that data, well, I don't know if FLUENT or CFDPost has a tool to do that or not, but I'm sure you can find a software to do that in the web, or you can built your own tool. Regards

September 26, 2015, 02:48
#10
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N B Khan
Join Date: Jan 2014
Posts: 39
Rep Power: 6
Quote:
 Originally Posted by gfoam Hi. If you are doing a transient simulation, you can plot the Cd, Cl and other force and moment coefficients as a function of time using the monitors in fluent. There are specific monitors of that coefficients in FLUENT and you can export them as chart in a ASCI file, everithing automatically with fluent. To do a FFT of that data, well, I don't know if FLUENT or CFDPost has a tool to do that or not, but I'm sure you can find a software to do that in the web, or you can built your own tool. Regards
Thanks dear for ur response,

In fluent, there is tool for FFT and we can find St number using the option of Magnitude in y axis and Strouhal number in X axis with uploading the Cl history file...
But I am unable to get the plot of FFT Vs time.....
similarly, I am also unable to get the FFT plot in CFD-post

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