Supersonic Condition at Outlet Boundary

ahmadijaz · December 11, 2017, 23:23

Greetings !

I am working on converging diverging nozzle. In this nozzle, combustion reaction takes place and the exhaust gases must leave the nozzle at supersonic conditions i-e at 2 or 3 Mach. I have clue to to my statement which says "Export boundary was dealt with supersonic speed" from paper which i am trying to reproduce.

Can anyone tell me what that statement means? or how can i set my boundary to supersonic condition?

Thanks.

Ravindra Shende · December 12, 2017, 01:24

The bc means to extrapolate all the variables at the exit boundary.

ahmadijaz · December 13, 2017, 00:48

thanks for the help sir.

how can i extrapolate my variables at the exit of nozzle as my domain ends at the nozzle exit?

are you taking about far-field thing?

Ravindra Shende · December 13, 2017, 04:26

I mean calculate the values of all the variables on the exit boundary by extrapolating the values at the interior points

juliom · December 13, 2017, 09:57

The gradient is zero for all the primitive variables, this is the main assumption with supersonic/hypersonic flows. This is widely accepted since all the characteristic leave the domain.
If you set the gradient to be zero at the outlet, basically you are saying that the primitive variables at the exit plane are the same from he plane right before the exit plane.

LuckyTran · December 14, 2017, 19:39

I don't really understand the question. In Fluent you don't need to do anything for a supersonic outlet.

December 11, 2017, 23:23	Supersonic Condition at Outlet Boundary	#1
ahmadijaz New Member Ahmad Ijaz Join Date: Jun 2017 Location: Islamabad, Pakistan Posts: 13 Rep Power: 8	Greetings ! I am working on converging diverging nozzle. In this nozzle, combustion reaction takes place and the exhaust gases must leave the nozzle at supersonic conditions i-e at 2 or 3 Mach. I have clue to to my statement which says "Export boundary was dealt with supersonic speed" from paper which i am trying to reproduce. Can anyone tell me what that statement means? or how can i set my boundary to supersonic condition? Thanks.

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December 12, 2017, 01:24		#2
Ravindra Shende Member Ravindra Shende Join Date: Feb 2011 Location: Pune, India Posts: 45 Rep Power: 15	The bc means to extrapolate all the variables at the exit boundary.

December 13, 2017, 00:48		#3
ahmadijaz New Member Ahmad Ijaz Join Date: Jun 2017 Location: Islamabad, Pakistan Posts: 13 Rep Power: 8	thanks for the help sir. how can i extrapolate my variables at the exit of nozzle as my domain ends at the nozzle exit? are you taking about far-field thing?

December 13, 2017, 04:26		#4
Ravindra Shende Member Ravindra Shende Join Date: Feb 2011 Location: Pune, India Posts: 45 Rep Power: 15	I mean calculate the values of all the variables on the exit boundary by extrapolating the values at the interior points

December 13, 2017, 09:57		#5
juliom Senior Member Julio Mendez Join Date: Apr 2009 Location: Fairburn, GA. USA Posts: 290 Rep Power: 18	The gradient is zero for all the primitive variables, this is the main assumption with supersonic/hypersonic flows. This is widely accepted since all the characteristic leave the domain. If you set the gradient to be zero at the outlet, basically you are saying that the primitive variables at the exit plane are the same from he plane right before the exit plane.

December 14, 2017, 19:39		#6
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,668 Rep Power: 65	I don't really understand the question. In Fluent you don't need to do anything for a supersonic outlet.