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November 23, 2011, 19:42 |
DRAG coefficient prediction
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#1 |
New Member
Join Date: Oct 2011
Posts: 4
Rep Power: 14 |
Hello
I'm trying to determinate the polars for an airfoil 2D and I created a test case with a NACA 0012 on openFOAM 2.0.1 I obtained very good value for lift and moment coefficient, while the drag coefficient is very strange related with the ABBOTT results I attached the compare between my results and the ABBOTT - the fvScheme and fvSolution are the same of the airfoil 2D tutorials - the boundary conditions are: { version 2.0; format ascii; class volVectorField; object U; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // dimensions [0 1 -1 0 0 0 0]; internalField uniform (69.62 0 7.32); boundaryField { inlet { type freestream; freestreamValue uniform (69.62 0 7.32); } outlet { type freestream; freestreamValue uniform (69.62 0 7.32); } body { type fixedValue; value uniform (0 0 0); } leftAndright { type empty; } } { version 2.0; format ascii; class volScalarField; object p; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // dimensions [0 2 -2 0 0 0 0]; internalField uniform 0; boundaryField { inlet { type freestreamPressure; } outlet { type freestreamPressure; } body { type zeroGradient; } leftAndright { type empty; } } { version 2.0; format ascii; class volScalarField; object nut; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // dimensions [0 2 -1 0 0 0 0]; internalField uniform 1.8766e-05; boundaryField { inlet { type freestream; freestreamValue uniform 1.8766e-05; } outlet { type freestream; freestreamValue uniform 1.8766e-05; } body { type nutUSpaldingWallFunction; value uniform 0; } leftAndright { type empty; } } { version 2.0; format ascii; class volScalarField; object nuTilda; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // dimensions [0 2 -1 0 0 0 0]; internalField uniform 7.25e-05; boundaryField { inlet { type freestream; freestreamValue uniform 7.25e-05; } outlet { type freestream; freestreamValue uniform 7.25e-05; } body { type fixedValue; value uniform 0; } leftAndright { type empty; } } rho = 1.225 kg/m^3 nu = 1.45e-05 m^2/s^2 - I used the Spalart-Allmaras turbulence model the yplus is near 90, that would be good, becuase is in the logaritmic BL I attached my mesh There is anyone that could help and explain why I obtained those results Last questions: in the forceCoeff.C file if these vector totForce = fm.first().first() + fm.first().second(); vector totMoment = fm.second().first() + fm.second().second(); scalar liftForce = totForce & liftDir_; scalar dragForce = totForce & dragDir_; scalar sideForce = totForce & sfDir_; scalar pitchMoment = totMoment & pitchAxis_; scalar Cl = liftForce/(Aref_*pDyn); scalar Cd = dragForce/(Aref_*pDyn); scalar Cy = sideForce/(Aref_*pDyn); scalar Cm = pitchMoment/(Aref_*lRef_*pDyn); what is fm.first() and the other term to calculate the totForce? Thank you for every useful answers! I need help! Andrea |
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