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-   -   Nozzle Entrainment (http://www.cfd-online.com/Forums/cfx/92292-nozzle-entrainment.html)

zephyrus17 September 9, 2011 03:00

Nozzle Entrainment
 
I've been trying to simulate entrainment into a domain by the action of a convergent nozzle. The nozzle jet blows perpendicular to the opening and air is sucked in simply by the pressure drop. The opening boundary condition is "Opening Pressure and Direction". The inlet is Total Pressure at 100 Pa.

However, I've encountered the issue where my CFX results of entrainment ratio (massFlow()@Opening/massFlow()@Inlet) are around 2x more than the the experimental results. This happens even if I create extremely small mesh sizes.

I read that extruding the opening face away from the actual location helps, though I'm not sure how. I've also tried "entrainment" as the boundary conditions, but have encountered convergence issues so I've stopped using "entrainment" as the boundary condition.

What are some advices that you could offer? Is it the boundary condition, mesh, or should I extrude the opening face further away?

ghorrocks September 9, 2011 07:04

You should always do a sensitivity study on parameters like mesh and boundary proximity. Nobody on the forum can answer this (unless they guess), you have to do the check and determine for yourself.

This FAQ has some useful tips:
http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

zephyrus17 September 12, 2011 01:38

Thanks for the link. I've seen that, but it's just so many factors that could affect this, and I was just hoping that someone with experience with this could help. Thanks for the assistance, though :)


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