Extract pressure to excel 3D plot

  • Last Post 30 November 2017
  • Topic Is Solved
Jimmyhan posted this 27 November 2017

Hi, I am Jimmy. I have gotten the pressure deviation result for a boundary, I can show them via cfx post contour. I would like to show this pressure result by excel 3D plot. can I use CFX post to do this directly? I found way to extract the pressure result to csv file which can be open by excel. but the pressure result was very very large, it should be depended on mesh I suppose. so it is very hard to draw 3D plot. Give me some advice. Thank you!

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peteroznewman posted this 27 November 2017

Hi Jimmy, when you say "the pressure result was very very large", I think you mean that the size of the csv file was very large, and yes, a smaller mesh element size will result in a larger number of data points covering the same area.

The Excel 3D surface plot is only useful to plot data on a perfect rectangular grid. Is that what your mesh has? Please post an image of your contour plot and the underlying mesh. I don't understand the benefit of a 3D surface plot over a contour plot of the same data. Perhaps you could explain why you want the 3D surface plot.

Regards, Peter

Jimmyhan posted this 28 November 2017

Thank you for your reply. pic is what I got and what kind of plot I want to transfer.my result

I would like to 

peteroznewman posted this 28 November 2017

Okay Jimmy, Excel is not capable of making a surface plot unless the data is on a rectangular grid, which you don't have due to the curved edges of the hole in the center. You can purchase an add-in that has this capability.

A more powerful program like matlab can make a 3D surface plot from x,y,z data, however, you will have to create a surface in the center, put a mesh on that surface and assign values to those nodes. Otherwise, the plotting algorithm will fill the hole in the center by interpolation of the data at the edges of the hole and that won't look pretty.

Why would you expend so much effort to make a 3D surface plot when the same information is conveyed by the contour plot? I don't understand the benefit.

Jimmyhan posted this 28 November 2017

Peter, you are right. I understand what you mean exactly. I don't know how to explain this to you. I have to say sometimes I really didn't get my supervisor order too. whatever, I really appreciate you give me such good information about CFX using.

raul.raghav posted this 28 November 2017

As @peteroznewman pointed out, why would you need a 3D surface plot when contours provide you the same data. And for your case since you have flow over a oval cylinder, the max pressure (at stagnation point) will cause a sharp bump in the 3D surface plot. And as peteroznewman mentioned,for the hole in the center, the data would be interpolated based on the data from the edges. See attached figures for contour and 3D surface plot (matlab) for a case of flow over a cylinder:


Jimmyhan posted this 29 November 2017

Hi Rahul, you gave me a figure which I just want to get. But unfortunately, I cant use Matlab anyway. I did not really understand the interpolation of the data of edges. As you know the pressure data was extracted from CFX post as csv file. what I should do is use a different expression method. Today I try to learn Matlab, it will be good news to me if you can give me some suggestion about Matlab using in CFX simulation.

raul.raghav posted this 29 November 2017

Any data you export from the plane of interest is going to be missing values at the empty/void region (oval section in your case). And for a surface plot, you need a uniform rectangular grid. So no matter which code you run (Matlab, Excel with the additonal addin, Origin etc.), the value of the exported data in the empty region will be interpolated based on the values at the edges of the empty region. I hope that helps!

Correct me if I'm wrong here, so you are saying that you want to export the data as an expression? And why if I may ask?

Creating surface plots are quite straightforward in Matlab particularly with improvements in the GUI. Refer link below:

MATLAB surface plot



Jimmyhan posted this 30 November 2017

You know, if I can get the 3D plot, why not try to use it for shear stress. so after learning Matlab using, maybe I can add in some expression for others parameters. from the website you gave me I found it is not too difficult to convert to 3D plots. Thank you so much for your guidance.