basic question about the pressure
Hi all,
This is very basic I think but I'd like to be sure about this: In the pressure file 0/p, we set the dimensions of the pressure such as we need to multiply the pressure by the fluid density to get "Pascal" as units. So, during the post-process, when we visualize the pressure, basically we need to multiply it by the fluid density to get the "real" pressure field. Am I right? Thanks. |
Hi,
Yes you are correct: [p]=m^2/s^2; P=p*rho -> [P]=kg/(ms^2)=Pa Regards, Jose Santos |
Thanks Jose.
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So, another question related. What about "nu" units?
Im running a very simple case, flow through a pipe, imposing p = 0.026 at inlet and 0 at outlet. (p dimensions are [0 2 -2 0 0 0 0], that is p is divided by rho). In transportProperties i set: nu nu [0 2 -1 0 0 0 0] 3.047e-6; Since the fluid im trying to simulate has a dinamic viscosity etha= 0.0032 Pa*s and densisty rho=1050 kg/m3. What i did was nu = 0.0032/1050 = 3.047e-6. When i try to compare results with analytical solution, Poiseuille´s flow, vmax (of the parabola developed) should be: vmax=(0.026 * r^2)/(4*L*nu) But vmax in the results is around half the expected. Should there be a mistake considering nu units? Which are the units of 3.047e-6? |
Fernando,
[0 2 -1 0 0 0 0] declares the nu dimensions as m^2 s^-1. I would say that your problem lies somewhere else, probably in the boundary conditions. Regards, Jose Santos |
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Jose, thanks for the reply. Lets see, the mesh consists of a pipe, with an inlet, the wall, and the outlet. The boundary conditios are:
0/p: dimensions [0 2 -2 0 0 0 0]; internalField uniform 0; boundaryField { wall { type zeroGradient; } inlet { type fixedValue; value uniform 0.026; } outlet { type fixedValue; value uniform 0; } } 0/U: dimensions [0 1 -1 0 0 0 0]; internalField uniform (0 0 0); boundaryField { pared { type fixedValue; value uniform (0 0 0); } entrada { type zeroGradient; } salida { type zeroGradient; } I cannot find an error. I attach the velocity profile at the outlet, it seems preetty parabolic, but the analitical solution predicts a parabolic profile with maximmum velocity of 0.47 m/s. Any idea? Im using simpleFoam, laminar, nu = 3.047e-6. Thanks |
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