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manoj_1 March 18, 2010 04:39

Single stage centrifugal pump
I am trying to analyse an existing single stage radial flow pump in CFX.
The impeller and the radial diffuser has been modelled separately in Bladegen. Then meshing is created in Turbogrid (including mesh statics improvement) after many trials.The problem definition is setup in CFX PRE using Turbomachinery wizard (i.e specifying meshfiles
for impeller and diffuser, rotational speed for the rotor, P inlet and mass flow out let, frozen rotor, S1 to R1 pitch change=1.17 (for this specific pump etc.)
However following problems are encountered when solver manager runs.
1.The following message appears

****** Notice ****** |
| A wall has been placed at portion(s) of an INLET |
| boundary condition (at 55.6% of the faces, 60.6% of the area) |
| to prevent fluid from flowing out of the domain. |
| The boundary condition name is: R1 Inlet. |
| The fluid name is: Water. |
| If this situation persists, consider switching |
| to an Opening type boundary condition instead.

I have observed that at high flow rates the %of blockage reduces ie. instead of 55.6% it is around 30%.

2. The solution initially converges then it does not converge.

3. However result files are obtained after running the problem for specified no. of iterations (100 to 200nos of iterations).
4. The results of analysis (static pressure rise at different flow rates)
varies by around 33% maximum from the test result.

Kindly advice on how to improve the results of analysis

ghorrocks March 18, 2010 07:50

The warning message simply means a recirculation has hit the inlet plane. Your convergence will be much better if you move the inlet plane further away so it does not cut through a recirculation.

manoj_1 March 22, 2010 02:14

Dear G. Horrocks
Thank you for your reply:). I have moved the inlet upstream, however struggling with the highly skewed mesh on the hub surface (in Turbogrid).
I have inserted control points in the mesh and tried to improve the mesh by moving the control points, but the mesh is not improving

soldimix15 September 5, 2010 11:31

Problem with Tgrid
1 Attachment(s)
Greetings. Im doing a single stage simulation under cavitation of a centrifugal pump, in fact, i am only simulating one blade passage. i have had a little bit of trouble on turbogrid, i want the inlet of the passage to be as far away of the blade as possible (meaning, on the very inlet of the impeller). I have imported the curves from Cfturbo 5.0. When i click on the option "Initialize points to full extents of Hub curve ", and then proceed to generate the passage, the following error appears

The hub radius at the inlet of the blade passage is too small. Try moving the blade passage inlet closer to the blade.

the geometry of the blade passage is the following
Attachment 4604
and as you can see, that is the place whre i want the inlet to be.

so my question is, how can i fix this error without moving too much the inlet from where i want it to be? right now i have ran the simulation without that option, and the default inlet surface is insside the passage near the blade, but i want to study the flow from the very inlet of the impeller. I would appreciate any help. Thanks

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