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-   -   Boundary Condition at outlet for supersonic flow (http://www.cfd-online.com/Forums/fluent/44460-boundary-condition-outlet-supersonic-flow.html)

Benjamin Zachariah April 17, 2007 11:33

Boundary Condition at outlet for supersonic flow
 
Hi,

I'm modelling an axisymmetric pipe flow from a compressed air canister at 8Bar (modelled as a pressure inlet) through a straight tube, into a constriction representing a valve, then again expanding into another tube, then into a C-D nozzle. As the flow will be supersonic, choked in the valve, then no boundary conditions should be imposed at the outlet of the nozzle, right? if this is the case, then what should i set the outlet boundary condition to be? the error i usually get is either floating point error, or some sort of divergence. any alterations of the URFs just delays the inevitable incorrect solution. i'm using the k-epsilon model, air is set as ideal gas, all the solution settings are second order, simple.

thanking you all for your assistance

Rohan April 18, 2007 04:04

Re: Boundary Condition at outlet for supersonic fl
 
Hi Benjamin,

Generally for high speed flows its better to run the simulation at a lesser speed and then use this result as a intial guess to avoid divergence or floating point errors.

Thanks

Regards

Rohan

Benjamin Zachariah April 19, 2007 07:07

Re: Boundary Condition at outlet for supersonic fl
 
will try. thanks.

Benjamin Zachariah April 19, 2007 07:11

Re: Boundary Condition at outlet for supersonic fl
 
a new error has just appeared that i've never seen before.

it's Error: Specific_Heat_by_T_Integral: invalid lower bound, T0 <= 0

any ideas?

thanks

Rohan April 23, 2007 00:47

Re: Boundary Condition at outlet for supersonic fl
 
Hi,

Looks like the T0 for the specific heat calculation is tending to zero.

Iam not sure why this is happening. Please carefully go through your boundary conditions.

Thanks

Regards

Rohan


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