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Cell sizes in export results incorrect?

Question asked by Thomas Wagner on Nov 20, 2019

Hello FlowSim users,

 

when doing flow simulation studies I often use the export results function to create text files with e.g. temperature and velocity for further processing. These text files also contain cell volumes but it seems to me as if these numbers are not correct.

 

To check I created a simple case of a pipe with a square cross section of 100 mm x 100 mm and 1000 mm length, which makes the liquid volume become 10,000,000 mm³. Activating the "Create fluid body assembly" in the "Check Geometry" function creates a body of exactly this volume.

 

For this simulation I only use a global mesh of type "manual" and set the cell size to 10 mm for all three directions. That gives 10 x 10 x 100 =  10,000 cells.

 

After having created the mesh using "Export Results" with the option "Use entire geometry" saves a text file for which I choose "Velocity" as the only additional variable to write out.

 

First strange thing: The very first line in this text file lists the variable/column names and surprisingly also states a variable "Surface [m^2]" although there is no such column in the text file.

 

With having chosen flow velocity as an additional variable to write out each data line should contain 5 values: x, y, z coordinates and volume for each cell, and velocity. But some data lines do not have a velocity value. These lines with only 4 values relate to cells to do not lie inside the liquid volume (at least this is my interpretation).

 

After cleaning the export file from all those lines with missing velocity value summing up all the single volume values does not produce the expected result: The total volume should be 0.01 m³, but I get 0.43 m³. A by far too high number!

Having checked this a couple of times and always coming to the same conclusion I have no idea where my thinking is wrong.

 

Can anybody confirm this discrepancy or probably knows what mistake I am making? Any help is very much appreciated.

 

Regards,
Thomas

 

P.S.: My system is Flow Simulation 2019 SP3 Build 4547 on a Windows 10 machine.

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