Turning supersonic flow into subsonic

Salexv · September 5, 2012, 05:58

Hello,
I have a supersonic converging-diverging inlet system using external and internal compression system.
My initial flow is Mach 3 and therefore, of course the flow throwout the whole inlet is supersonic.
I am trying to achieve a subsonic outlet of the inlet by increasing the pressure outlet. But it doesn't work because in supersonic flows, Fluent doesn't consider outlet pressure.
So how can I force the flow to become subsonic even though I can't change the pressure outlet?
Thanks

eng_s_sadeghi · September 5, 2012, 08:51

You can not force the outlet to achieve a pressure. Flow regime defines what should happen at the outlet

Salexv · September 5, 2012, 09:08

Thank you for your response.

So what you are saying is that there is no way to receive a supersonic inlet with a subsonic outlet (having a normal shock in the diverging part of the system)? In any way possible?

eng_s_sadeghi · September 5, 2012, 09:34

It depends just on boundary condition (not outlet) and geometry.

Salexv · September 5, 2012, 09:42

What condition do you think should I enter on the outlet? Tried changing it into "pressure inlet" and it didn't help.

flotus1 · September 5, 2012, 12:17

The problem is that in a supersonic flow, the flow field is not affected by the conditions downstream. Thus, the flow field in a given geometry is independent of the values you try to specify at the outlet.

Your only chance (if the upstream values are fixed) is to change the geometry.

Salexv · September 23, 2012, 10:35

Can someone help me please with this problem?
I've seen few works that managed to apply a high pressure outlet in a supersonic inlet, but couldn't reach the authors.
Does anyone know how to enforce it in FLUENT?
Thanks

syavash · September 23, 2012, 21:10

Quote:

Originally Posted by Salexv

Can someone help me please with this problem?
I've seen few works that managed to apply a high pressure outlet in a supersonic inlet, but couldn't reach the authors.
Does anyone know how to enforce it in FLUENT?
Thanks

Hi Alexander,

I have a similar problem and I couldn't manage to find a solution.
There is an image of the geometry and Mach contours that I upload here.
How is it possible to get this solution?! Anyone knows it?

September 5, 2012, 05:58	Turning supersonic flow into subsonic	#1
Salexv New Member Alexander Join Date: Sep 2012 Posts: 4 Rep Power: 14	Hello, I have a supersonic converging-diverging inlet system using external and internal compression system. My initial flow is Mach 3 and therefore, of course the flow throwout the whole inlet is supersonic. I am trying to achieve a subsonic outlet of the inlet by increasing the pressure outlet. But it doesn't work because in supersonic flows, Fluent doesn't consider outlet pressure. So how can I force the flow to become subsonic even though I can't change the pressure outlet? Thanks

September 5, 2012, 08:51		#2
eng_s_sadeghi Member Join Date: Mar 2011 Posts: 64 Rep Power: 15	You can not force the outlet to achieve a pressure. Flow regime defines what should happen at the outlet __________________ Saeed Sadeghi Ansys Fluent CFD Consultant

September 5, 2012, 09:34		#4
eng_s_sadeghi Member Join Date: Mar 2011 Posts: 64 Rep Power: 15	It depends just on boundary condition (not outlet) and geometry. __________________ Saeed Sadeghi Ansys Fluent CFD Consultant

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September 5, 2012, 09:08		#3
Salexv New Member Alexander Join Date: Sep 2012 Posts: 4 Rep Power: 14	Thank you for your response. So what you are saying is that there is no way to receive a supersonic inlet with a subsonic outlet (having a normal shock in the diverging part of the system)? In any way possible?

September 5, 2012, 09:42		#5
Salexv New Member Alexander Join Date: Sep 2012 Posts: 4 Rep Power: 14	What condition do you think should I enter on the outlet? Tried changing it into "pressure inlet" and it didn't help.

September 5, 2012, 12:17		#6
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,427 Rep Power: 49	The problem is that in a supersonic flow, the flow field is not affected by the conditions downstream. Thus, the flow field in a given geometry is independent of the values you try to specify at the outlet. Your only chance (if the upstream values are fixed) is to change the geometry.

September 23, 2012, 10:35		#7
Salexv New Member Alexander Join Date: Sep 2012 Posts: 4 Rep Power: 14	Can someone help me please with this problem? I've seen few works that managed to apply a high pressure outlet in a supersonic inlet, but couldn't reach the authors. Does anyone know how to enforce it in FLUENT? Thanks