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-   -   axisymmetric annulus modelling (http://www.cfd-online.com/Forums/fluent/41540-axisymmetric-annulus-modelling.html)

shashikant June 27, 2006 14:38

axisymmetric annulus modelling
 
hi, I am comfused how to model annulus flow, using axis symmetry, i am not able to decide which is the correct way to model

I am modeling in gambit

pls help

shashikant

Jason June 27, 2006 17:11

Re: axisymmetric annulus modelling
 
Model a cross section of your annular geometry in the X-Y plane, where the axis of rotation of your annular geometry occurs at y=0 (the X-Axis).

Hope this helps, Jason

shashikant June 27, 2006 17:32

Re: axisymmetric annulus modelling
 
the c/s is a rectangular of say 5mm X 1000mm size and IF my inner dia is 10 mm this rectangle will be at 5 mm distance from x axis, NOW there is no edge at Y=0 to be called as axis

so i creadt a real edge at y=0, and label it axis now if I expoet the mesh i get the following error

WARN: Boundary Entity axis.8 does not contain valid entity an is not written

IS THIS method of modelling CORRECT

shashikant

Jason June 28, 2006 07:53

Re: axisymmetric annulus modelling
 
No. You don't need to create an edge to represent an axis in annular flows. Fluent already knows the X-Axis is your axis of rotation.

The Axis boundary condition is only used when the axis of rotation is in the fluid volume (i.e. the centerline of a pipe). Otherwise Fluent would treat the BC as a wall, which isn't realistic... you don't typically have an infinitely thin wire running down the centerline of a pipe. That's the only reason to use an Axis BC.

For your geometry, just model the 5mmX1000mm rectangle that's 5mm from the X axis... that's it. When you run Fluent, make sure to change the solver to Axisymmetric. That's all there is to it.

Hope this helps, and good luck Jason


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