[erkampasha]

I have an hypersonic flow internal case. In user guide, it said that "Should the flow become locally supersonic, the specified pressure will no longer be used; pressure will be extrapolated from the flow in the interior. All other flow quantities are extrapolated from the interior." However when i change the backflow pressure, mach number of exit plane is changed. Secondly, in hypersonic case example in official tutorial case fluent document, pressure outlet is set 25 Pa. If it were surpass, the value would have been zero.

Could you help me about clarifying the issue?

[LuckyTran]

There are no hard constraints at supersonic outlets that needs defining. However, you need to make sure that it is supersonic first. There are boundary conditions that will result in a subsonic flow, namely too high a pressure.

Set a low enough pressure such that the exit becomes supersonic. If you set a high enough backflow pressure, the outlet becomes an inlet!

[erkampasha]

Originally Posted by LuckyTran

There are no hard constraints at supersonic outlets that needs defining. However, you need to make sure that it is supersonic first. There are boundary conditions that will result in a subsonic flow, namely too high a pressure.

Set a low enough pressure such that the exit becomes supersonic. If you set a high enough backflow pressure, the outlet becomes an inlet!

already i set the values for inlet bc according to given total variables values in experiment paper. I set operating pressure 0 and inlet pressure is 557 Pa inlet temp 436 K. However i do not know what should i do for outlet. In openfoam and cfd++, i was setting supersonic outlet or zero gradient.

[LuckyTran]

To be even more clear, use a pressure outlet and set a low enough pressure such that the flow becomes supersonic.

[erkampasha]

Originally Posted by LuckyTran

To be even more clear, use a pressure outlet and set a low enough pressure such that the flow becomes supersonic.

i use pressure outlet and use the default value 0 Pa. Is it enough low pressure?