# Problem Boundary Conditions, forceCoeff

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 February 18, 2014, 06:13 Problem Boundary Conditions, forceCoeff #1 New Member   valerio galluzzi Join Date: Jan 2014 Posts: 9 Rep Power: 12 Hello everyone, i'm a phd student of engineering and i'm new using openfoam. I'm trying to simulate a flow around a circular cylinder. The first time i reached good results using a flow velocity inlet condition and now i want to do the same thing but using the gauge pressure inlet condition. My problem is i'm not sure about the new boundary condition and how to set up the force and forceCoeff files. The results of the second simulation were really bad, the mean Cd and mean Cl were too big, like 10e4 O_o. i hope someone can help me, because i cant understand if there is a problem inside the P and U boundary condition files or there is a problem inside the forceCoeff file or both of them. Re=8900 --------------------------------------- InitialCondition file: flowVelocity (0 0 0); pressure 28.4; turbulentKE 6.9646e-1; turbulentOmega 4.3923e2; nut_initial 0; #inputMode merge --------------------------------------- P file: #include "include/initialConditions" dimensions [0 2 -2 0 0 0 0]; internalField uniform \$pressure; boundaryField { In { type fixedValue; value uniform \$pressure; } Out { type fixedValue; value \$internalField; } Up&Bottom { type fixedValue;; value \$internalField; } Wall { type zeroGradient; } Left&Right { type empty; } } ---------------------------------------------- U file #include "include/initialConditions" dimensions [0 1 -1 0 0 0 0]; internalField uniform \$flowVelocity; boundaryField { In { type inletOutlet; inletValue uniform (0 0 0); value \$internalField; } Out { type inletOutlet; inletValue uniform (0 0 0); value \$internalField; } Up&Bottom { type inletOutlet; inletValue uniform (0 0 0); value \$internalField; } Wall { type fixedValue; value uniform (0 0 0); } Left&Right { type empty; } } -------------------------------------------------------- force file forces { type forces; functionObjectLibs ("libforces.so"); //Lib to load outputControl timeStep; outputInterval 1; patches (Wall); // change to your patch name pName p; UName U; rhoName rhoInf; // Indicates incompressible nuName nuInf; log true; rhoInf 1.225; // Redundant for incompressible nuInf 1.45e-05; //Reference kinetic viscosity for fluid liftDir (0 1 0); dragDir (1 0 0); CofR (0 0 0); // Origin for moment calc pitchAxis (0 0 1); magUInf 6.814; lRef 0.019; // Characteristic length Aref 2.8338e-4; // Estimated } --------------------------------------------------------- forceCoeff file forceCoeffs { type forceCoeffs; functionObjectLibs ( "libforces.so" ); outputControl timeStep; outputInterval 1; patches ( Wall ); pName p; UName U; rhoName rhoInf; // Indicates incompressible log true; rhoInf 1.225; // Redundant for incompressible liftDir (0 1 0); dragDir (1 0 0); CofR (0 0 0); // Origin for moment calc pitchAxis (0 0 1); magUInf 6.814; lRef 0.019; // Characteristic length Aref 2.8338e-4; // Estimated } -------------------------------------------------------------------- xerxes92005 likes this.

 February 20, 2014, 05:24 #2 New Member   valerio galluzzi Join Date: Jan 2014 Posts: 9 Rep Power: 12 someone!? pls, i really need help! xerxes92005 likes this.

 April 20, 2014, 12:15 #3 New Member   Amin S Join Date: Mar 2014 Posts: 5 Rep Power: 12 Hi Valerio. I`m almost working on the same problem. simulating flow around single and tandem cylinders using OpenFOAM. I`m a beginner with OpenFOAM and started few weeks ago. my primitive simulation includes a single cylinder subjected to uniform steady current with Re=3900. I deliberately chose Re=3900 because lots of works in literature have used this Re and my model can be crosschecked and verified comparing to their results. I run simulations using icoFOAM, simpleFOAM and PisoFoam but i haven't got acceptable results yet. maybe you can upload our folders here in order to check our results together and I can upload mine as well. Amin

 April 22, 2014, 04:48 #4 New Member   valerio galluzzi Join Date: Jan 2014 Posts: 9 Rep Power: 12 Hi xerxes! Finally someone has my same issue. As u have already read i use Re=8900, k-omegaSST turbulence model with wall-functions for k,omega, and nut and the solver is pimplefoam. What i found looking up in internet is probably a problem with the turbulence model. The k-omegaSST has problems when the Re is too low, like less than 10e+4. I couldnt try the k-epsilon model because i cant make it works, at least so far, and now i work on another things. But others have tried it and said it's better....i dont know. Write me ur email in pvt, because the files are too heavy for the forum. xerxes92005 likes this.

 May 1, 2014, 17:37 #5 New Member   Amin S Join Date: Mar 2014 Posts: 5 Rep Power: 12 Valerio, you may find this thread useful: http://www.cfd-online.com/Forums/ope...ng-fluent.html

 May 7, 2014, 08:36 #6 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 26 Did you try if any change in numerical parameters changes the solution? What if you decrease the time step? Or if you increase the length from inlet to your bluff body? __________________ The skeleton ran out of shampoo in the shower.

 May 7, 2014, 09:04 #7 New Member   valerio galluzzi Join Date: Jan 2014 Posts: 9 Rep Power: 12 i evaluated the time step by the courant number (less than 0.8) because i know the strouhal should be 0.21-0.22. I didnt try to change the distance from the inlet, but i used a reliable distance (well, i think it's reliable because the literature) 10.5 Diameters.

 May 7, 2014, 09:07 #8 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 26 What are the other boundary conditions (nut, k, omega)? Also, you wrote in the private message to me, that Fluent also fails. __________________ The skeleton ran out of shampoo in the shower.

May 7, 2014, 09:55
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valerio galluzzi
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Those are the BB
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 May 7, 2014, 11:16 #10 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 26 This file looks really strange. Something is wrong here... __________________ The skeleton ran out of shampoo in the shower.

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