Pressure drop consistently lower than measured with SimpleFoam
I'm trying to simulate the pressure drop through a small rectangular duct with a 90 degree bend. I've measured the pressure drop at 70m^3/h to be around 165Pa but my simulations are always 50-60Pa lower than that. Hopefully someone can see what I'm doing wrong. Am I defining a boundary condition incorrectly?
Control Dict Code:
application simpleFoam; Code:
ddtSchemes Code:
solvers Code:
transportModel Newtonian; Code:
simulationType RAS; Code:
dimensions [0 1 -1 0 0 0 0]; Code:
dimensions [0 2 -2 0 0 0 0]; Code:
dimensions [0 2 -2 0 0 0 0]; Code:
dimensions [0 0 -1 0 0 0 0]; Code:
dimensions [0 2 -1 0 0 0 0]; |
Hi!
What is your fluid? In simpleFoam p is a kinematic pressure (pressure/rho) so you will have to multiply the pressure drop with the fluid density to get the pressure in Pa. If you already did that, just ignore this reply. |
2 Attachment(s)
Thanks I did make that mistake but I'm still out by a quite a bit after taking it into account. I ran the simulation again with the relaxationFactors brought down to 0.15 and the endTime extended to 10000. The pressure difference (attached) averages around 99. The fluid is air and the conditions during the measurement were Lab air Temp 19.2°C and Atmospheric Pressure 29.3 inHg so the density is around 1.18kg/m^3 I think. That means simpleFoam predicts the pressure drop as 99*1.18=116.82Pa at 70m^3/h while the measurement is 162m^3/h.
I'm running it again currently with a finer mesh to try rule that out as the problem. |
These residuals are quiet high and based on your attached file I would say that this simulation is not converged...
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2 Attachment(s)
Okay from reading other posts I had taught that it was because of the turbulence and once the residuals had leveled off it was as close as I'd get to converged. The finer mesh has just converged with a pressure difference of 93 (110Pa) at the last time step. I'll try lowering the residual controls to:
Code:
p 1e-3; |
It did not converged either.
Check your pressure. It is still increasing. For convergence you should check some physical values if they are not changing anymore, not the residuals. In your case you should run as long as your pressure drop is not changing anymore. |
Thanks for the feedback, I've been focusing too much on the residuals. I'll work on getting results with a stable pressure result.
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