Reference Pressure

[selim]

Hi,

I want to be sure about the pressure value for the reference pressure.
In one of the tutorials for the compressible flow, the reference pressure is taken as 1e5.

When I use ElmerGUI or ElmerFront, the reference values for the specific heat ratio 1.4 (OK), but for the pressure it is set 0.0 by default (can be changed??)

Which value should I take?
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My second question is about the outlet pressure value.
It is stated in one of the tutorials that setting y component of the velocity--- implies pressure is 0??
I am also confused about it.

Thanks,
Selim

[Juha]

Hi,

you should usually set the "Reference Pressure" when dealing with compressible
flows. An alternative is to set "initial" and "external" pressure values such that absolute
pressure values may be used to compute the density values. It will, however, usually
be beneficial convergencewise to use the pressure deviation as the primary variable
(i.e. specify "Reference Pressure") as opposed to absolute pressure ("Reference
Pressure=0").

If the normal velocity at some boundary is "free", the natural boundary condition
states that p ~ p_ext for that boundary (for a developed flow), which is by default 0.
This natural boundary condition, if present, will fix the (deviation from reference)
pressure level, even for incompressible flows.

Regards, Juha