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[OpenFOAM] High pressure range using totalpressure BC

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Old   February 5, 2019, 11:59
Default High pressure range using totalpressure BC
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Dear foamers;
I have been trying to understand how pressure works in incompressible flow solvers (PISO in my case) and i found out that pressure in Navier Stokes has no physical meaning but just the gradient.
So i tried to find a good BC to couple velocity and pressure and gives me a good results for my project but the pressure in Parafoam makes no sense to me.

My BC are as follow;
Pressure:
Inlet: zerogradient
Outlet: totalpressure
P0 1.5e5
Gamma 0.0
Value uniform 0

Velocity:
Inlet: fixedvalue
Value uniform (25 0 0)
Outletressureinletoutletvelocity
Value uniform(0 0 0)

My project is only on an open test section that is symmetric and cst area, you can consider it as a simple jet of air, inflow and outflow.

I can't get the pressure to give me a good result, the velocity in the other hand works perfectly if i can say so!
The pressure range is so high and has negative values.
Since this is incompressible, there are a lot of pressure fluctuations.

Can anybody helps me please.
I have been trying for months to get this to work.
Here are some pictures of what it looks like. One for velocity and the rest pressure.
Thankx in advance!
Attached Images
File Type: jpg Resized_20190130_135024.jpg (68.4 KB, 11 views)
File Type: jpg Resized_20190130_135021.jpg (91.8 KB, 10 views)
File Type: jpg Resized_20190130_135017.jpg (94.4 KB, 7 views)
File Type: jpg Resized_20190130_135014.jpg (90.7 KB, 9 views)
File Type: jpg Resized_20190130_135105.jpg (79.1 KB, 7 views)
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Old   September 10, 2020, 08:54
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Tobias Kienzler
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As you mentioned only the pressure gradient is relevant for incompressible solvers, so could just as well set p0 to zero. But more importantly (and what screwed me up for a while) the solver uses kinematic pressure as described at https://www.openfoam.com/documentati...-pressure.html. This means p is not in Pascal but in mē/sē and must be rescaled by rho to actually make sense (and your p0 would have to be divided by rho in return, so 1.5e5 really only makes sense for a density of ca. 1). This rescaling is also relevant in the transportProperties, where nu = mu/rho is used instead of mu!
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