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Simulation of fluid flowing across a heated pipe |
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December 14, 2021, 13:00 |
Simulation of fluid flowing across a heated pipe
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#1 |
New Member
Cesare
Join Date: Dec 2021
Posts: 3
Rep Power: 5 |
Hello Foamers,
I'm new to the world of OpenFOAM and since I'm not at all sure about what I'm doing I'd like to have a few pieces of advice about a simulation I'm currently running. I'm trying to analyze water flowing in a spiral shaped, heated pipe. The data in my possession are: - the flow rate at the inlet; - the temperature at the inlet; - the heat flux across the walls, in terms of power; I'm running a 8.5 mln cells mesh which does not have any problem according to both my pre-processor and checkMesh. I'm using buoyantSimpleFoam as a solver to reach a steady state solution. I've tried multiple combinations of BCs I've found searching on this forum, but still when I'm running the simulation, the calculation for p_rgh shoots to 1000 iterations and the convergence is not at all good for this parameter. As far as I understood if I provide a condition for the velocity at the inlet, then I should provide a zeroGradient condition for p_rgh at the same boundary, and the same happens for the outlet patch, if I set the velocity condition at the inlet to zeroGradient I should provide an outlet condition for p_rgh. Still, if I do this, the calculation gives enormous continuity errors. Then I tried to adjust the continuity by also imposing a flow rate at the outlet. That solved the continuity problem, but I don't know if I did the right thing there at all. I'm thinking that I should initialize my fields better, but I don't have a clue about how to do it with such a complex geometry. As for the turbulence properties, the Re inside the pipe is around 20000, I'm using a low y+ (around 5) approach for my mesh and a KwSST model. In summary, I'm trying to use flowRateInletVelocity for U and since I'm sure that I'm making a big mess for not having understood or thought about something crucial, I'd like to know what are the right conditions to set for the outlet velocity and for the pressure boundaries if I don't know the pressure drop across my pipe. I will attach part of my bcs here for completeness, thanks to everyone willing to help |
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December 15, 2021, 08:34 |
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#2 |
Member
Lukas
Join Date: Sep 2021
Posts: 36
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Hello,
your pressure boundarys are not correct. U need to have at least one fixed pressure at inlet or outlet. normally u fix the pressure at the outlet i.e. type fixedValue on p_rgh u normaly also use fixedFluxPressure instead of zeroGradient. fixedFluxPressure -> when u have a defined velocity on this boundary(walls, inlet, etc) outlet does not have a defined velocity typical so no fixedFluxPressure hope that helps |
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December 15, 2021, 10:28 |
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#3 | |
New Member
Cesare
Join Date: Dec 2021
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Quote:
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December 16, 2021, 01:45 |
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#4 |
Member
Lukas
Join Date: Sep 2021
Posts: 36
Rep Power: 5 |
Yes u shall use fixedValue for the Outlet .
but the fixedFluxpressure is NOT fixing the pressure value, it "just" ensure the Flux is fixed to a value that is belonging to the velocity condition. Flux is the phi field value. Today i also have watched your velocity (U) file : Please never use a massflow condition on inlet AND outlet this is very bad. Best for convergence is always : Massflow on inlet and FixedPressure at the outlet only use something else if you don't have one of these informations cheers Last edited by Pappelau; December 16, 2021 at 03:11. |
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December 17, 2021, 05:48 |
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#5 |
New Member
Cesare
Join Date: Dec 2021
Posts: 3
Rep Power: 5 |
Thank you very much for the informations! I have a much clearer view on the interactions between the various BCs the software provides now
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February 11, 2022, 08:04 |
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#6 |
New Member
Outside North America
Join Date: Nov 2021
Posts: 14
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Hi, I've been using buoyantSimpleFoam on a flow and heat transfer problem in a tube and the turbulence model is KOmegaSST, but I get an error as soon as I run. Can you help me understand why that is? Thank you!
***** Starting time loop Time = 1 DILUPBiCGStab: Solving for Ux, Initial residual = 1, Final residual = 0.0105904, No Iterations 1 DILUPBiCGStab: Solving for Uy, Initial residual = 1, Final residual = 0.0062613, No Iterations 1 DILUPBiCGStab: Solving for Uz, Initial residual = 1, Final residual = 0.0125236, No Iterations 1 DILUPBiCGStab: Solving for h, Initial residual = 1, Final residual = 0.00863299, No Iterations 1 DICPCG: Solving for p_rgh, Initial residual = 0.974927, Final residual = 0.00959291, No Iterations 13 time step continuity errors : sum local = 135.963, global = 0.022484, cumulative = 0.022484 [0] [0] [0] --> FOAM FATAL ERROR: [0] Attempt to cast type calculated to type nutWallFunction [0] [0] From function To& Foam::refCast(From&) [with To = const Foam::nutWallFunctionFvPatchScalarField; From = const Foam::fvPatchField<double>] [0] in file /home/ubuntu/OpenFOAM/OpenFOAM-8/src/OpenFOAM/lnInclude/typeInfo.H at line 114. [0] FOAM parallel run aborting [0] [1] [1] [1] --> FOAM FATAL ERROR: [1] Attempt to cast type calculated to type nutWallFunction [1] [1] From function To& Foam::refCast(From&) [with To = const Foam::nutWallFunctionFvPatchScalarField; From = const Foam::fvPatchField<double>] [1] in file /home/ubuntu/OpenFOAM/OpenFOAM-8/src/OpenFOAM/lnInclude/typeInfo.H at line 114. [1] FOAM parallel run aborting [1] [2] [2] [2] --> FOAM FATAL ERROR: [2] Attempt to cast type calculated to type nutWallFunction [2] [2] From function To& Foam::refCast(From&) [with To = const Foam::nutWallFunctionFvPatchScalarField; From = const Foam::fvPatchField<double>] [2] in file /home/ubuntu/OpenFOAM/OpenFOAM-8/src/OpenFOAM/lnInclude/typeInfo.H at line 114. [2] FOAM parallel run aborting [2] [3] [3] [3] --> FOAM FATAL ERROR: [3] Attempt to cast type calculated to type nutWallFunction ****** I guess there's something wrong with the nut file setup, but I don't know what's wrong? ****** FoamFile { version 2.0; format ascii; class volScalarField; location "0"; object nut; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // dimensions [0 2 -1 0 0 0 0]; internalField uniform 0; boundaryField { INLET { type nutLowReWallFunction; value uniform 0; } OUTLET { type nutLowReWallFunction; value uniform 0; //type calculated; //value uniform 0; } WALL { type nutkWallFunction; value uniform 0; } } ******* |
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Tags |
buoyantsimplefoam, flowrateinletvelocity, pipe flow, thermal |
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