# Impinging Jet Boundary Conditions

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January 8, 2012, 01:11
#21
New Member

MK
Join Date: Aug 2009
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Quote:
 Originally Posted by elisun Hi. I've got a problem with modeling an impinging jet with fluent. do i have to model the nozzle too? i mean since the flow has to be fully developed in the outlet of the nozzle, do i need to create the geometry of a pipe in gambit , or it's enough to just consider the exit of nozzle? Tnx alot.
it depends on tha H/D ratio. if the distance betveen nozzle exit and impinging wall is small, the velocity profile at the nozzle outlet may affect on the ressults, specially at the stagnation point. but i think you should set a fully developed profile at the nozzle exit with UDF. for laminar flow, you can use a parabolic distribution like this:
u(r)=u_max (1-(r/R)^2),
where
u_max=1.5*u_avg, for 2D cartesian
u_max=2*u_avg, for axisymmetric problem
for turbulent flow, you can use 1/7 law but I think the velocity distribution does not affect the results severly.

 January 8, 2012, 01:16 #22 New Member   MK Join Date: Aug 2009 Posts: 22 Rep Power: 9 dear Anindya! you should consider to your computatinal domain. the width of domain (from symmetric plane to outlet) must be large enough to use pressure or outflow condition (say 10 to 15 times more than D). also, you should note that what kind of impinging geometry you have (i.e., confined or unconfined).

January 10, 2012, 16:45
#23
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anush
Join Date: Jan 2012
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hi, everybody i am new to the gambit and fluent software, and i needed help solving a converging nozzle problem,i am not getting the convergence in iterations, its actually showing lot of divergence during iteration process,
and it ends with warning like reverse flow at outlet and turbulent flow at outlet.
i have selected viscous flow to be -spalart allamaras and the courant number as 5. i have used solver as density based and fluid as Air(property-ideal gas).
As the iteration progresses the reverse flow and turbulent flow error is shown, after 80-90 iterations it shows divergence and accordingly it reduces the courant number from .5 to 5e-5 for each iterations and it ends with floatation error.

below is image of my model- the white region is wall, the pink region is pressure far field, and grey(ish) region is pressure inlet.
i need to find the flow characteristics of compressible flow in nozzle.
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January 11, 2012, 00:22
#24
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MK
Join Date: Aug 2009
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Quote:
 Originally Posted by flashkicker9 hi, everybody i am new to the gambit and fluent software, and i needed help solving a converging nozzle problem,i am not getting the convergence in iterations, its actually showing lot of divergence during iteration process, and it ends with warning like reverse flow at outlet and turbulent flow at outlet. i have selected viscous flow to be -spalart allamaras and the courant number as 5. i have used solver as density based and fluid as Air(property-ideal gas). As the iteration progresses the reverse flow and turbulent flow error is shown, after 80-90 iterations it shows divergence and accordingly it reduces the courant number from .5 to 5e-5 for each iterations and it ends with floatation error. below is image of my model- the white region is wall, the pink region is pressure far field, and grey(ish) region is pressure inlet. i need to find the flow characteristics of compressible flow in nozzle. plz plz plz reply asap... thank you for your time
Dear Flashkicker9!

I think the problem is caused by your pressure far field boundary. there is a limitation to use this kind of condition, that the far-filed boundary should not have broken edge (like a cube) you must use a curved surface instead of broken one. use a half-sphere instead of this cube.

January 11, 2012, 14:40
#25
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anush
Join Date: Jan 2012
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Quote:
 Originally Posted by takin Dear Flashkicker9! I think the problem is caused by your pressure far field boundary. there is a limitation to use this kind of condition, that the far-filed boundary should not have broken edge (like a cube) you must use a curved surface instead of broken one. use a half-sphere instead of this cube.
thank you it helped me solve for 2d and i am gonna try for 3d, but what condition to take for the compressible flow?

 February 27, 2016, 13:58 Modelling 2D jet impingement on a flat plate #26 New Member   Mark Join Date: Feb 2016 Posts: 1 Rep Power: 0 Hi All, I am tasked with modelling a 2d axisymmetric jet impingement on a flat plate but I have no clue how to begin modelling this. Can anyone help with this? Thanks Mark

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