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-   -   Backflow in nozzle exit (combustion chamber with nozzle) (https://www.cfd-online.com/Forums/fluent/227763-backflow-nozzle-exit-combustion-chamber-nozzle.html)

the_sixth_hokage June 9, 2020 07:15
Backflow in nozzle exit (combustion chamber with nozzle)
 
Hi..
I'm modelling a 3d combustion chamber with nozzle...the operating pressure are very high and fuels used are CH4 and liquid Oxygen (cryogenic temperature)

Inlets : 8MPa
Outlet : tried both 0MPa and 101325 Pa

Operating conditions: 6MPa

I am getting backflow in the outlet and the setup diverges...my mesh is good and have no skewness at exit or inside chamber and nozzle..my mesh is fine..

I even tried long slender gradually increasing length mesh at outlet so that the backflows stop..

My outlet pressure outlet backflow specification: Normal to boundary...

Anyone knows how to solve this...??!!

vinerm June 15, 2020 06:37
Conditions
 
It appears to be a compressible flow. Use value of 0 Pa as operating pressure and apply all boundary pressure values as absolute values. You may also want to choose non-reflecting condition at the outlet.

the_sixth_hokage June 15, 2020 08:51
Quote:
Originally Posted by vinerm (Post 774482)
It appears to be a compressible flow. Use value of 0 Pa as operating pressure and apply all boundary pressure values as absolute values. You may also want to choose non-reflecting condition at the outlet.
Yeah..I'm using SRK real gas equations..my outlet is a pressure outlet and how do I set it as a non reflecting condition??

vinerm June 15, 2020 08:55
Nrbc
 
That option is available within boundary condition panel. Open pressure outlet and you will see Acoustic condition options.


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