Backflow in nozzle exit (combustion chamber with nozzle)

the_sixth_hokage · June 9, 2020, 08:15

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, 07:37

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, 09:51

Quote:

Originally Posted by vinerm

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, 09:55

That option is available within boundary condition panel. Open pressure outlet and you will see Acoustic condition options.

June 9, 2020, 08:15	Backflow in nozzle exit (combustion chamber with nozzle)	#1
the_sixth_hokage Member Lee Jo Join Date: Mar 2020 Posts: 30 Rep Power: 6	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...??!!

June 15, 2020, 07:37	Conditions	#2
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 36	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. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

June 15, 2020, 09:55	Nrbc	#4
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 36	That option is available within boundary condition panel. Open pressure outlet and you will see Acoustic condition options. the_sixth_hokage likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

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