Supersonic and subconic outlet

March 29, 2007, 03:58

I have a problem in modelling a Laval nozzle. I can choose only subsonic or supersonic outlet boundary condition in CFX. But really there are subsonic regions near wall and supersonic region dar from walls. So, what should I do?

March 29, 2007, 22:43

If it's mostly supersonic just run supersonic.

March 30, 2007, 09:59

Thank you, HekLeR. I tried, but when I applied supersonic condition, I didn't get any solution (fatal overflow solver error). When I applied subsonic condition, I got M<<1 at exit.

April 2, 2007, 17:04

Probably you still need to run supersonic, but you might have to play with the timestep, eg: smaller maybe....

The problem may be that part of the outlet is subsonic, temporarily, and then there is no way for the system to physically feel the specified pressure.

You might play with stopping the solver just before it blows to see what the solution is looking like. i.e. why is it going bad?

March 29, 2007, 03:58	Supersonic and subconic outlet	#1
Dmitry Guest Posts: n/a	I have a problem in modelling a Laval nozzle. I can choose only subsonic or supersonic outlet boundary condition in CFX. But really there are subsonic regions near wall and supersonic region dar from walls. So, what should I do?

March 29, 2007, 22:43	Re: Supersonic and subconic outlet	#2
HekLeR Guest Posts: n/a	If it's mostly supersonic just run supersonic.

March 30, 2007, 09:59	Re: Supersonic and subconic outlet	#3
Dmitry Guest Posts: n/a	Thank you, HekLeR. I tried, but when I applied supersonic condition, I didn't get any solution (fatal overflow solver error). When I applied subsonic condition, I got M<<1 at exit.

April 2, 2007, 17:04	Re: Supersonic and subconic outlet	#4
HekLer Guest Posts: n/a	Probably you still need to run supersonic, but you might have to play with the timestep, eg: smaller maybe.... The problem may be that part of the outlet is subsonic, temporarily, and then there is no way for the system to physically feel the specified pressure. You might play with stopping the solver just before it blows to see what the solution is looking like. i.e. why is it going bad?