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Uncertainty in CFX post node count

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Old   November 6, 2007, 07:04
Default Uncertainty in CFX post node count
  #1
Adam
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Hi,

In trying to decribe my turbomchinary rotor grid in a report, I need to find the dimensions of the node count (ie hub to shroud, inlet to outlet, periodic to periodic etc).

If i create a polyline along the boundary intersection of say Inlet and Shroud, Inlet and Periodic, and Periodic and Shroud, I can output the node count using the function calculator in the tools tab.

However, the results given, when multiplied together do not give the correct total node count, when compared with turbogrid or the solver input.

Does anyone know why this is the case?

Many thanks

Adam
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Old   November 6, 2007, 10:07
Default Re: Uncertainty in CFX post node count
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CycLone
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Hi Adam,

Multiplying the nodes in this manner will only give you the right node count if you have a single block structured mesh. Although it is possible to create a mesh of this topology in TurboGrid, it is highly unlikely that you did since it would be of very poor quality.

A better estimate would be to take the number of nodes in a spanwise plane (at the hub or shroud, for instance) and multiply this by the number of nodes from hub to shroud.

That said, why are you doing this in the first place? Just run the grid diagnositcs and you'll get the exact node count, or double click on the domain to see individual domain statistics, or use the solver output, or look at the grid section of the automatically generated report, or... you get the point.

Sounds like a pointless academic exercise you prof might have put you up to.

-CycLone
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Old   November 6, 2007, 10:26
Default Re: Uncertainty in CFX post node count
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Adam
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I'm sorry CycLone, but I think you have misunderstood my question.

I know the actual node count from the diagnostics etc, but I want to show the number of nodes in each direction, i.e. hub to shroud, inlet to outlet, and periodic to periodic in order to indicate the characteristics of the mesh.

Unfortunately, I don't think you can get from turbogrid the complete hub to shroud etc if you use some of the automatic features, such as hub to tip expansion for tip to shroud tip gap.

That is why I have created a polyline from hub to shroud etc to try and ascertain the node count in each direction. Unfortunately, if you multiply the node count in each of the 3 directions together, it comes up significantly less than the actual node count.

Hope this helps

Many thanks

Adam

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Old   November 6, 2007, 10:39
Default Re: Uncertainty in CFX post node count
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CycLone
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Hi Adam,

It's different because the topolgy isn't uniform. If you look at the mesh you can see why. There will be fewer nodes across the inlet than between the blades, for instance, because the blade probably has an O-Grid around it. TurboGrid automatically calculates the topology to best fit the geometry.

You can view some of these parameters in turbogrid if you look at the other tabs in the Mesh object, you can control them as well.

-CycLone
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