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CFX not writing mesh coordinates correctly when exported 

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March 22, 2017, 09:30 
CFX not writing mesh coordinates correctly when exported

#1 
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AHMAD
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Hi all,
I have done a simulation on a axial type rotor compressor. I am trying to export data from CFD Post and I would like to calculate averaged values using Matlab from the data I wish to export. I want to calculate the averaged values of velocity of the outlet plane at a constant radius line. So, I exported the Velocity and Radius(Both values are selected from the list of variables that are available to export) values at the outlet using the export function from the File drop down menu in CFD Post. When I did that, I found that the values of radius is not constant along the pitch whereas it should be constant. For example, the radius at the Hub and Shroud should have a constant values of radius. When I drew the domain, I am certain that I specified a constant radius at the hub and shroud. Can somebody help me why the data is not giving me data along a constant radius? 

March 22, 2017, 10:02 

#2 
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To make it clear, I have attached a image of a plot that I made. It is clear that the radius at the shroud is not constant and varying.


March 22, 2017, 16:50 

#3 
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Glenn Horrocks
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It will have something to do with the way you drew the geometry, the way you meshed it or the way you are extracting the data. You are going to have to look at all those steps on your model carefully and figure out where the variation comes from.


March 23, 2017, 05:15 

#4 
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Hi Ghorrocks,
I tried extracting the polyline at the shroud outlet. I got the same results. I am pretty sure that I had a constant radius at the hub and radius when drawing the geometry. Cheers 

March 23, 2017, 05:46 

#5 
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Glenn Horrocks
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Please post on image of your geometry and where you polyline you are using is located. Also include an image of your mesh.


March 23, 2017, 06:07 

#6 
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The green line is the polyline at Shroud line of the Outlet Plane.
The grids are hexahedral and generated using ICEM. 

March 23, 2017, 17:22 

#7 
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Glenn Horrocks
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You are going to have to show more information than that if we are going to help you...


April 6, 2017, 10:42 

#8 
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AHMAD
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Hi Ghorroks
Sorry for the late reply. I have been quite busy lately. There are several images that I have attached. The first image is coordinate points at the outlet plane hub line from ICEM. The second one is a plot of the hub line radius using the coordinates that I obtained from ICEM. **radius =sqrt(X^2 + Y^2). Coordinates are in cm. I realized that I am able to obtain a constant hub radius if I round the digits after the decimal points to the desired significant figures. However, I have a really small y+ value(less than 2). This means that significant figures after the decimal are important and rounding them will not allow me to capture the values near to the boundary(hub line). The third and fourth image is a plot of the grid using matlab. You can clearly see that the hub line is not constant. As mentioned earlier , I intend to draw a constant radius line from the hub line to the shroud. I will then use this line as a grid to interpolate my results from CFX. I am interested in finding the average along the pitch line of my domain. Basically it is the same as drawing polylines in CFD Post but will get the same results( not constant line) when exporting the polylines and plotting the lines in MATLAB. I hope that you can understand what I am trying to explain. best 

April 6, 2017, 17:52 

#9 
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Glenn Horrocks
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Location: Sydney, Australia
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Is this variation in your geometry? Or your mesh? What about if you use the double precision solver?


April 7, 2017, 09:58 

#10 
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AHMAD
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I tried using a double precision solver but the results are pretty much the same.
I drew a polyline at the intersection of the hub and outlet hence obtaining the hub line. Then I plotted the radius against theta of the polyline. If I zoom out the graph, it will look like a constant radius line. 

Tags 
ansys, cfdpost, export data, matlab 
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