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-   -   2.5D simulation in CFX-pre (http://www.cfd-online.com/Forums/cfx/94174-2-5d-simulation-cfx-pre.html)

yvonne November 8, 2011 10:47

2.5D simulation in CFX-pre
 
Hi All, Im carrying out 2.5D simulation of centrifugal pump.The following is the procedure Ive used to make the geometry
  • As my geometry consists of 3 domains: Inlet(stationary), Impeller(rotating) and Outlet(stationary), I created the 3domains separately; i.e. 3 different ICEM files.
  • I followed the general 2.5D procedure: surface mesh followed by extrusion in the z-direction, separately naming the lateral faces which will be later initialized as symmetry.
  • Exported the 3 mesh files separately in .cfx5 format
  • Imported the 3 mesh files into CFX-pre
  • Created interfaces in CFX-pre and thus joined the 3 domains.
  • This worked for me and CFX simulated my 2.5D model.
Now, the problem Im facing is as follows:
There is a problem in the way CFX is calculating inlet and outlet areas. It is calculating the areas exactly an order of magnitude less than actual because of which the velocities calculated are an order of magnitude more; this results in a highly unrealistic value of pressure being calculated. Is there a way to rectify this problem? I checked out if I could write a CEL, but seems, CEL is just for post processing and for extracting calculated quantities.

Can anybody throw some light on this?

ghorrocks November 8, 2011 17:45

You have either a geometry/mesh problem which is making the faces too big or small, or you are scaling them in CFX-Pre.

You should always check the scale of the model is correct in CFX-Pre before proceeding.

yvonne November 9, 2011 05:01

1 Attachment(s)
Thanks for you reply. The point to be noted is, as its a 2.5D model, Im having curves instead of surfaces, so in essence CFX instead of calculating surface areas is calculating curve length (I suppose) multiplied by the one layer thickness in z-direction. Im attaching the 2D geometry. Please note that instead of outlet face Im having a 'line' and instead of inlet face Im having a 'curve'

ghorrocks November 9, 2011 06:18

Well, that will be your problem then. The flow rate is calculated over the one element thickness which is likely to be tiny. And I am guessing you assumed that would match the full geometry? So you need to convert the flow rates into flow per unit length.

yvonne November 10, 2011 02:01

Ok Thanks Glenn, youve got me thinking.. Ill think on those lines. I was considering the full flowrate

ghorrocks November 10, 2011 05:34

Many others have made that mistake. You are not the first.

When CFX finally introduce a proper 2D solver the problem will be fixed.


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