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Pressure drop in a pipe - Different results Fluent vs. Analytical |
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August 29, 2018, 13:21 |
Pressure drop in a pipe - Different results Fluent vs. Analytical
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#1 |
Member
Liliana de Luca Xavier Augusto
Join Date: Feb 2013
Posts: 68
Rep Power: 13 |
Hello all,
I am simulating a very simple caso of a flow in a 2D horizontal pipe (0,2 m diameter and 1m length). Fluid Density = 827 kg/m³ Fluid Viscosity = 0.026 Pa.s Inlet = parabolic velocity profile with vmax = 0.016 m/s Outlet = pressure-outlet with P = 0 The flow is laminar. So I calculated by hand the pressure drop along the pipe, since it is laminar, fully developed and newtonian fluid with: dP = rho * (L/D) * (64/Re) * ((v_ave)^2)/2 Then I got arount 0.17. In Fluent I got 0.083. For this, I analyzed static pressure. Even with total pressure, the result is not the same (0.098). Does anyone have a similar problem? |
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August 29, 2018, 15:27 |
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#2 |
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,739
Rep Power: 66 |
Just a sanity check, what is the massflow rate that Fluent outputs?
What's your mesh look like? Did you already do a grid dependence study? You'll be surprised how fine a mesh you need for this simple problem. Also just fyi, this type of problem is really good for simulating using the periodic boundary condition rather than velocity inlet and pressure outlet. |
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August 29, 2018, 15:31 |
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#3 | |
Member
Liliana de Luca Xavier Augusto
Join Date: Feb 2013
Posts: 68
Rep Power: 13 |
Quote:
The mass flow rate at inlet is 1.32 kg/s. |
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August 29, 2018, 20:44 |
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#4 |
Senior Member
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August 29, 2018, 20:45 |
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#5 |
Member
Liliana de Luca Xavier Augusto
Join Date: Feb 2013
Posts: 68
Rep Power: 13 |
I have found the problem. I did not use axisymmetry. Now it matchs perfectly.
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May 14, 2021, 09:45 |
Pressure drop varying in pipes - fluent vs Openfoam
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#6 |
Member
Vishnu
Join Date: May 2019
Location: Tamilnadu, India
Posts: 55
Rep Power: 7 |
Hello everyone,
My case is to compare the fluent and openfoam pressure drop results for simple straight pipe. Pipe datas - Diameter 20mm and 0.2m long. Solver - simpleFoam And the pipe is splitted into three parts (60mm,80mm,60mm totally 200mm). and i am using cyclicAMI boundary type for interiors. I am using k-omega turbulence model and dictionary files are as per in the tutorial. Before using this, i have used realizable k epsilon, but it leads to higher dp, so i changed to k-omega and it gives better results in many projects. Ansys fluent results and experimental results are exactly matched. Yes, the total pressure drop of openfoam is also reaches very close to an experimental results. But the cutoff dp (i.e individual pipe dp) was not matching with fluent. In percentage wise, the cutoff dp is high (greater than 10%). Fluent results and experimental results: pipe-1 = 3.5 mbar, pipe-2 = 3.82 mbar, pipe-3 = 2.8 mbar, total dp = 10.12mbar OF results: pipe-1 = 4.02 mbar, pipe-2 = 3.4 mbar, pipe-3 = 2.25 mbar, total dp = 9.67mbar y+ plus value for the pipe is max:2.18 and min:0.16, minimum cell size is 0.005mm. U file Code:
internalField uniform (0 0 0); boundaryField { massflow-inlet { type fixedValue; value uniform (0 0 -2.65); } pressure-outlet { type inletOutlet; value uniform (0 0 0); inletValue uniform (0 0 0); } wall-pipe-1 { type fixedValue; value uniform (0 0 0); } wall-pipe-2 { type fixedValue; value uniform (0 0 0); } wall-pipe-3 { type fixedValue; value uniform (0 0 0); } pipe121 { type cyclicAMI; } pipe122 { type cyclicAMI; } pipe231 { type cyclicAMI; } pipe232 { type cyclicAMI; } } Code:
dimensions [0 2 -2 0 0 0 0]; internalField uniform 99.858; boundaryField { massflow-inlet { type zeroGradient; } pressure-outlet { type fixedValue; value $internalField; } wall-pipe-1 { type zeroGradient; } wall-pipe-2 { type zeroGradient; } wall-pipe-3 { type zeroGradient; } pipe121 { type cyclicAMI; } pipe122 { type cyclicAMI; } pipe231 { type cyclicAMI; } pipe232 { type cyclicAMI; } } Code:
internalField uniform 0.0095; boundaryField { massflow-inlet { type turbulentIntensityKineticEnergyInlet; intensity 0.05; value uniform 0.0095; } pressure-outlet { type inletOutlet; inletValue uniform 0.0095; Value uniform 0.0095; } wall-pipe-1 { type kqRWallFunction; value uniform 0.0095; } wall-pipe-2 { type kqRWallFunction; value uniform 0.0095; } wall-pipe-3 { type kqRWallFunction; value uniform 0.0095; } pipe121 { type cyclicAMI; } pipe122 { type cyclicAMI; } pipe231 { type cyclicAMI; } pipe232 { type cyclicAMI; } } Code:
internalField uniform 127; boundaryField { massflow-inlet { type fixedValue; value $internalField; } pressure-outlet { type zeroGradient; } wall-pipe-1 { type omegaWallFunction; value $internalField; } wall-pipe-2 { type omegaWallFunction; value $internalField; } wall-pipe-3 { type omegaWallFunction; value $internalField; } pipe121 { type cyclicAMI; } pipe122 { type cyclicAMI; } pipe231 { type cyclicAMI; } pipe232 { type cyclicAMI; } } Code:
internalField uniform 0; boundaryField { massflow-inlet { type calculated; value uniform 0; } pressure-outlet { type calculated; value uniform 0; } wall-pipe-1 { type nutkWallFunction; value uniform 0; } wall-pipe-2 { type nutkWallFunction; value uniform 0; } wall-pipe-3 { type nutkWallFunction; value uniform 0; } pipe121 { type cyclicAMI; } pipe122 { type cyclicAMI; } pipe231 { type cyclicAMI; } pipe232 { type cyclicAMI; } } Code:
solvers { p { solver GAMG; tolerance 1e-08; relTol 0.05; smoother GaussSeidel; cacheAgglomeration on; nCellsInCoarsestLevel 20; agglomerator faceAreaPair; mergeLevels 1; } "(U|k|epsilon|omega)" { solver smoothSolver; smoother symGaussSeidel; nSweeps 2; tolerance 1e-07; relTol 0.1; } } SIMPLE { nUCorrectors 2; nNonOrthogonalCorrectors 0; residualControl { p 1e-10; U 1e-10; "(k|epsilon|omega|f|v2)" 1e-10; } } relaxationFactors { fields { p 0.3; } equations { U 0.5; k 0.7; epsilon 0.7; omega 0.7; } } Code:
ddtSchemes { default steadyState; } gradSchemes { default Gauss linear; } divSchemes { default none; div(phi,U) bounded Gauss linearUpwind grad(U); div(phi,k) bounded Gauss limitedLinear 1; div(phi,epsilon) bounded Gauss limitedLinear 1; div(phi,omega) bounded Gauss limitedLinear 1; div(phi,v2) bounded Gauss limitedLinear 1; div((nuEff*dev2(T(grad(U))))) Gauss linear; div(nonlinearStress) Gauss linear; } laplacianSchemes { default Gauss linear corrected; } interpolationSchemes { default linear; } snGradSchemes { default corrected; } wallDist { method meshWave; } Thank you in advance, Vishsel |
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