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Re: value of Drag force, lift force, and pressure unexpected |
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September 1, 2022, 11:23 |
Re: value of Drag force, lift force, and pressure unexpected
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#1 |
New Member
Mehulbhai Sasvadiya
Join Date: Jan 2021
Location: Germany
Posts: 25
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Hello to all
I got some different values of cl and cd snd pressure as well. My case is a 2D airfoil; the flow comes from a downward Y direction to the upward Y. U=10.5 m/s and moving wall boundary condition. this is my pimple simulation file HTML Code:
ExecutionTime = 39151.23 s ClockTime = 40502 s forceCoeffs forces execute: Coefficients Cd : -132.7221 (pressure: -133.06389 viscous: 0.34178725) Cs : 1.6577795e-16 (pressure: 1.6569721e-16 viscous: 8.0738118e-20) Cl : 303.84677 (pressure: 303.33214 viscous: 0.51462964) CmRoll : 1.202228 (pressure: 1.2001917 viscous: 0.0020362308) CmPitch : 22.873064 (pressure: 22.553154 viscous: 0.31990978) CmYaw : 0.52514043 (pressure: 0.52649277 viscous: -0.0013523468) Cd(f) : -65.158823 Cd(r) : -67.563278 Cs(f) : 0.52514043 Cs(r) : -0.52514043 Cl(f) : 174.79645 Cl(r) : 129.05032 streamLine streamLine1 write: seeded 0 particles Tracks:0 Total samples:0 continuityError continuityError1 write: local = 2.0707245e-11 global = 2.4884514e-14 cumulative = -3.2172443e-12 functionObjects::vorticity vorticity writing field: vorticityField yPlus yPlus write: writing field yPlus patch airfoil y+ : min = 0.23817668, max = 154.31507, average = 52.044156 fieldAverage fieldAverage1 write: Calculating averages Writing average fields End |
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September 2, 2022, 00:37 |
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#2 |
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Ashutosh
Join Date: Jul 2021
Location: India
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The simple answer is your simulation is diverging. If that is not the case then you have used wrong boundary or initial conditions.
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September 3, 2022, 05:21 |
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#3 | |
New Member
Mehulbhai Sasvadiya
Join Date: Jan 2021
Location: Germany
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Quote:
How can I know that my initial boundary or boundary condition is wrong? please check my boundary file HTML Code:
6 ( left { type cyclicAMI; inGroups 1(cyclicAMI); nFaces 715; startFace 138650; matchTolerance 0.0001; transform unknown; neighbourPatch right; AMIMethod faceAreaWeightAMI; restartUncoveredSourceFace 1; } right { type cyclicAMI; inGroups 1(cyclicAMI); nFaces 715; startFace 139365; matchTolerance 0.0001; transform unknown; neighbourPatch left; AMIMethod faceAreaWeightAMI; restartUncoveredSourceFace 1; } inlet { type patch; nFaces 80; startFace 140080; } outlet { type patch; nFaces 80; startFace 140160; } airfoil { type wall; inGroups 1(wall); nFaces 310; startFace 140240; } leftRight { type empty; inGroups 1(empty); nFaces 139600; startFace 140550; } ) |
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September 3, 2022, 08:52 |
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#4 |
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Ashutosh
Join Date: Jul 2021
Location: India
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Can you show your model in diagram? I have just noticed that y+ value is very high (assuming you are using a low- Reynolds Turbulence Model).
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September 3, 2022, 09:34 |
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#5 |
New Member
Mehulbhai Sasvadiya
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Location: Germany
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September 3, 2022, 11:33 |
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#6 |
Member
Ashutosh
Join Date: Jul 2021
Location: India
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The model you are using for simulation.
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September 3, 2022, 11:35 |
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#7 |
New Member
Mehulbhai Sasvadiya
Join Date: Jan 2021
Location: Germany
Posts: 25
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September 3, 2022, 11:42 |
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#8 |
New Member
Mehulbhai Sasvadiya
Join Date: Jan 2021
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I have attached file here please check it
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September 3, 2022, 12:12 |
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#9 |
Member
Ashutosh
Join Date: Jul 2021
Location: India
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I am not sure what you trying to achieve, your Inlet has normal in x direction but it has velocity value in y direction. Are you trying to rotate airfoil to change angles of attack?
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September 3, 2022, 12:14 |
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#10 | |
New Member
Mehulbhai Sasvadiya
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Quote:
My inlet is IN Y-direction upward and outlet is top od Y-direction and have moving wall left and right as mentioned in blockMesh. I am not trying to change AOA. Thanks |
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September 3, 2022, 12:19 |
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#11 |
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Ashutosh
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Are you using dynamic mesh in your simulation?
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September 3, 2022, 12:21 |
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#12 |
New Member
Mehulbhai Sasvadiya
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Location: Germany
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September 4, 2022, 15:35 |
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#13 |
New Member
Mehulbhai Sasvadiya
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Location: Germany
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September 5, 2022, 02:59 |
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#14 |
Member
Ashutosh
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Location: India
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One thing I noticed is nut value is 0 in initial condition. I would choose it 0.1 times of nu. Since you are not using dynamic Mesh there is no point in using AMI Interpolation. It just add additional computation cost. Last thing I will suggest is reducing max Co in controlDict to 5 from 20.
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September 5, 2022, 03:16 |
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#15 | |
New Member
Mehulbhai Sasvadiya
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Quote:
I have periodic boundary the left and right walls. Do u think I should use MRF Property? I still do not understand why I can not use AMI interpolation? Thanks |
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September 5, 2022, 03:22 |
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#16 |
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Ashutosh
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You can use periodic boundary condition for that. AMI and MRF are mainly used when mesh motion is involved.
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September 5, 2022, 03:25 |
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#17 |
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Mehulbhai Sasvadiya
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September 5, 2022, 03:32 |
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#18 |
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Ashutosh
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I am talking about this https://www.openfoam.com/documentati...ed-cyclic.html
Here you can get more Info periodic set up - cyclicAMI |
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September 5, 2022, 04:01 |
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#19 | |
New Member
Mehulbhai Sasvadiya
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Quote:
After reading this I have not found any wrong with my Boundary conditions. Have you seen anything wrong? |
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September 5, 2022, 04:24 |
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#20 |
Member
Ashutosh
Join Date: Jul 2021
Location: India
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I don't understand why are using cyclic boundary condition? Your simulation involves measuring Cd and Cl on a airfoil. Anyways you probably need to edit nut initial condition and run the simulation. And also add log file of your simulation if you encounter any error it helps a lot.
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