I am trying to model the flow from an air bottle (8000 psi at 1500C) through a 0.25" orifice to the atmosphere. (14.7 psi, 72F)
An incompressible model yields a maximum flow of mach 2.479 -- so I tried a compressible flow.
8000 psi, 1500C, and mach 2.479 implies a total temperature of 6109..86 rankine and a total pressure of 132,286.98 psi. (right ?)
with boundary conditions of "unknown: and 0 psi ... using a transient analysis with a microsecond step
by 1 millisecond -- I find a pressure in the vessel of -2400 psi (negative ?) and a temperature of 5650 F
Suggestions ...
/Steven
Hi Steven,
Are you setting these as initial conditions?
Do you have air set to variable or is it still incompressible?
I would not advise both unknown AND p=0, just use unknown for now perhaps. Otherwise you are leaving it free and constraining it at the same time.
Kind regards,
Jon
Hi Paul,
Please do and let us know. It may well be that you need a pressure, just not both conditions at once.
Typically we use unknown for compressible models but usually when we have a prescribed mass flow rate at the inlet, here this is unknown so it might be more suitable to assign a known pressure. So long as it really is the true pressure on the plane you are assigning it.
Would you be able to share the support file (CFZ) with us at all?
Best regards,
Jon