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obtaining significantly different Flow profiles after only changing Mesh size |
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June 30, 2020, 13:06 |
obtaining significantly different Flow profiles after only changing Mesh size
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#1 |
New Member
berat
Join Date: Jun 2020
Posts: 6
Rep Power: 6 |
Hello,
so i am new to OpenFOAM and simulation in general and i am currently trying to simulate a two dimentional pipe flow. I managed to obtain a satisfiying result/flow profile in my simulation. Now I am looking to making the simualtion bigger by simply changing the value form the "converttoMeter" command in the BlockMesh file. When i do so i am getting a completly unrealistic flow profile, even though every other part of the Simualtion is exactly the same. I allready tried increasing/decreacing the velocity at the input patch, this didnt change anything though. BlockMesh of the working Simulation: convertToMeters 0.000001; vertices ( (0 0 0) (35000 0 0) (35000 3500 0) (0 3500 0) (0 0 65) (35000 0 65) (35000 3500 65) (0 3500 65) ); blockMesh of the faulty simulation convertToMeters 1; vertices ( (0 0 0) (35000 0 0) (35000 3500 0) (0 3500 0) (0 0 65) (35000 0 65) (35000 3500 65) (0 3500 65) ); as i already mentioned the rest of the simulation is exactly the same, despite me tryed to change up the velocity which didnt change anything though. now i am curious what i am doing wrong. i would appreate the sightest hints which would help me solve my problem. |
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June 30, 2020, 16:07 |
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#2 |
Senior Member
Troy Snyder
Join Date: Jul 2009
Location: Akron, OH
Posts: 220
Rep Power: 19 |
In your faulty simulation, the length scales are increased dramatically. Correspondingly, your Reynolds number has increased significantly given the same U and fluid properties rho and mu.
Is the solution converging for the high-Re case? Is the flow modeled as laminar or turbulent? |
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July 1, 2020, 12:28 |
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#3 | ||
New Member
berat
Join Date: Jun 2020
Posts: 6
Rep Power: 6 |
thank you, I never concidered the reynolds number. But i calculated the Reynolds number by hand and get 2.17. so i should still have laminar flow.
Quote:
Do i have any other options of assuring convergence besides implementing relaxationFactors? Quote:
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July 1, 2020, 13:14 |
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#4 |
Senior Member
Troy Snyder
Join Date: Jul 2009
Location: Akron, OH
Posts: 220
Rep Power: 19 |
Using incompressible piso in openfoam, the only fluid property to specify is kinematic viscosity. What value did you prescibe for this and the inlet velocity for the faulty mesh case? I
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July 1, 2020, 13:22 |
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#5 |
New Member
berat
Join Date: Jun 2020
Posts: 6
Rep Power: 6 |
Code:
transportModel Newtonian; nu nu [ 0 2 -1 0 0 0 0 ] 1; CrossPowerLawCoeffs { nu0 nu0 [ 0 2 -1 0 0 0 0 ] 1; nuInf nuInf [ 0 2 -1 0 0 0 0 ] 1; m m [ 0 0 1 0 0 0 0 ] 1; n n [ 0 0 0 0 0 0 0 ] 1; } BirdCarreauCoeffs { nu0 nu0 [ 0 2 -1 0 0 0 0 ] 1; nuInf nuInf [ 0 2 -1 0 0 0 0 ] 1; k k [ 0 0 1 0 0 0 0 ] 0; n n [ 0 0 0 0 0 0 0 ] 1; } Code:
dimensions [0 1 -1 0 0 0 0]; internalField uniform (0 0 0); boundaryField { inlet { type fixedValue; value uniform (0.62e-3 0 0); } outlet { type zeroGradient; } walls { type noSlip; } } Code:
DimensionedConstants { unitSet micro; microCoeffs { universal { c c [ 0 1 -1 0 0 0 0 ] 2.99792e+8; // speed of light in vacuum (µm/µs) G G [ -1 3 -2 0 0 0 0 ] 6.67429e-20; // gravitational constant (µm^3/(pgµs^2)) h h [ 1 2 -1 0 0 0 0 ] 6.62607e-13; // Planck's constant (pgµm^2/µs) } electromagnetic { e e [ 0 0 1 0 0 1 0 ] 1.602176634e-4; // elementary charge (pC) } atomic { me me [ 1 0 0 0 0 0 0 ] 9.10938e-16; // electron mass (pg) mp mp [ 1 0 0 0 0 0 0 ] 1.67262e-12; // proton mass (pg) } physicoChemical { mu mu [ 1 0 0 0 0 0 0 ] 1.66054e-12; // atomic mass unit (pg) k k [ 1 2 -2 -1 0 0 0 ] 1.38065e-8; // Boltzman constant (pgµm^2/µs^2K) } standard { //- Standard pressure [pg/µmµs^2 ] Pstd Pstd [ 1 -1 -2 0 0 0 0 ] 1e2; // 1 pg/µmµs^2 //- Standard temperature [degK] Tstd Tstd [ 0 0 0 1 0 0 0 ] 298.15; // should be same as in SI unit system } } } |
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July 1, 2020, 13:28 |
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#6 |
New Member
berat
Join Date: Jun 2020
Posts: 6
Rep Power: 6 |
kinematic viscosity is 1
velocity is (0.62e-3 0 0) i should also metion, that i have been using the "unitSet micro" command which is supposed to change the units into micro. so its not kg,m etc anymore, but rather μg, μm etc. |
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