[Arkadiy Kr]

As i understood, Absolute Pressure can be computed as sum of Pressure and ref. Pressure, but in my case CFX acts in different way, and should know that way! Please help!!
I attached pics from my case, ref. Pressure = 5,5 [atm]

[Opaque]

By any chance, did you activate the buoyancy model ? You may be seeing the hydrostatic pressure contribution as well.

[Arkadiy Kr]

Buoyancy model is activated and i tried to account it by creating an expression (Pressure+Density*g*Y+Reference Pressure), but at the and, i didn't get values equal to Absolute Pressure
So how i can get values of Absolute Pressure using Pressure?

[Arkadiy Kr]

Originally Posted by Opaque

By any chance, did you activate the buoyancy model ? You may be seeing the hydrostatic pressure contribution as well.

Thx for answer, I used this formula: Absolute Pressure = Pressure + Reference Pressure + Hydrostatic Pressure, where Hydrostatic Pressure = Reference Density * g * h.

But i'm still confused about Pressure Drop. I can not use Pressure difference between top and bottom levels, as I get negative values which is not physically possible and I can not use Absolute Pressure difference between top and bottom levels, as Hydrostatic Pressure assumes that domain is filled by only one fluid, but it's not.

[Opaque]

If your calculation of the hydrostatic pressure assumes anything about the number of fluids, it is incorrect.

Have you tried computing the hydrostatic pressure as

(Fluid 1.Volume Fraction * Fluid 1.Density + Fluid 2.Volume Fraction * Fluid 2.Density ) * ( g . (position vector - reference location) )

That should account for the weight of the column of fluid. Notice the . to account for any possible orientation as well as the reference location (which I assume you provided to the software)

[Arkadiy Kr]

Originally Posted by Opaque

If your calculation of the hydrostatic pressure assumes anything about the number of fluids, it is incorrect.

Have you tried computing the hydrostatic pressure as

(Fluid 1.Volume Fraction * Fluid 1.Density + Fluid 2.Volume Fraction * Fluid 2.Density ) * ( g . (position vector - reference location) )

That should account for the weight of the column of fluid. Notice the . to account for any possible orientation as well as the reference location (which I assume you provided to the software)

I used this formula in CFD-Post, when i tryed to find values of Absolute Pressure using Pressure. By the way, I found out that value of Reference Density has a strong influence over accurate culculation of Pressure. Results for Pressure and Absolute Pressure which i represented above is wrong. When i use value of Reference Density equal to gas density I get right values of Pressures. (First time I used value of liquid density). The reason I write it here, I've read that Reference value of Density is not important for culculation.

Originally Posted by ghorrocks

I think you misunderstand the purpose of the reference value. The exact value of this parameter should not matter and it certainly does not vary over the domain. It is a single value used to reduce numerical round-off. You should be able to double or halve it and results are unaffected.

If changing the reference value changes your results then you have a very sensitive simulation and you should be using double precision numerics.

P.S. Double precision and Single pecision numerics give me almost the same results!!!