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Posts: 31
Registered: ‎10-26-2011
Accepted Solution

Inlet Boundary Conditions ?

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11-11-2011 06:45 AM

I'm modeling a simple nozell to investigate an air amplification scheme.  The input to the nozell is compressed air at about 100 PSI - I'm not sure what the best type of load to use for this - the fan surface doesn't seem to work well - If I use the Surface Pressure / Traction object - not sure which option to use - Static pressure or Total Pressure or other, like traction - can someone explain which of these options would work best for understanding resulting velocity and pressure out the end of the nozzel, and what traction pressure is ?





ps:  here is a cross section of the model to show you inputs and outputs - red is input, both front and back of nozzel are inlet / outlets with no other constraints.



chamfer on casing.png


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Posts: 259
Registered: ‎06-14-2010

Re: Inlet Boundary Conditions ?

11-13-2011 09:14 AM in reply to: tim.sefton

For this internal flow, same physical problem can be modelled either following two ways with the speficied BCs and the ways of validating result.

(a) Spcify Inlet pressure +outlet pressure, validate result at flow rate (or velocity)

(b) Specify inlet velocity (or flowrate) + outlet pressure(or inlet/outlet BC), validate average pressure drop from inlet to outlet

Numerically (b) is stable than (a), and one of the special case is setting outlet pressure=0 (or set inlet/outlet BC). 

It appears that you have convergence issue according your posted image, I suggest that you change your modelling to (b) and make sure the mesh is good condition.


Jianhui Xie, Ph.D
Principal Engineer
MFG-Digital Simulation
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