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[waves2Foam] What should lref and Aref be for surface piercing cylinder in waves?? |
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February 12, 2016, 08:40 |
What should lref and Aref be for surface piercing cylinder in waves??
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Senior Member
ArielJ
Join Date: Aug 2015
Posts: 127
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Hi everyone,
I'm running a multiphase case with regular waves (using waveFoam) passing a vertical surface piercing cylinder and I'm trying to calculate the forces and force coefficients. I have them set up and they are being calculated and in the right place, but the values look very very wrong. 1) First of all, the values for the drag and lift coefficients are oscillating... does this suggest that they are not converging? I expected to see one value after the wave has reached the cylinder. The values not only are changing, but massively increase. 2) Is it even possible to use the forces and forceCoeffs function objects as they are with a multiphase solver?? I'm wondering if I have defined the phases incorrectly? Or if I need to separate the U and p values somehow into U.water and U.air, etc? For instance, I am confused in my transportProperties file because I have the transport model set to Newtonian, so I commented out all other information (BirdCarreauCoeffs, CrossPowerLawCoeffs), as shown below: Code:
phases (water air); water { transportModel Newtonian; nu nu [ 0 2 -1 0 0 0 0 ] 1e-06; rho rho [ 1 -3 0 0 0 0 0 ] 1028; /* CrossPowerLawCoeffs { nu0 nu0 [ 0 2 -1 0 0 0 0 ] 1e-06; nuInf nuInf [ 0 2 -1 0 0 0 0 ] 1e-06; m m [ 0 0 1 0 0 0 0 ] 1; n n [ 0 0 0 0 0 0 0 ] 0; } BirdCarreauCoeffs { nu0 nu0 [ 0 2 -1 0 0 0 0 ] 0.0142515; nuInf nuInf [ 0 2 -1 0 0 0 0 ] 1e-06; k k [ 0 0 1 0 0 0 0 ] 99.6; n n [ 0 0 0 0 0 0 0 ] 0.1003; } */ } air { transportModel Newtonian; nu nu [ 0 2 -1 0 0 0 0 ] 1.568e-05; //1.48e-05; --> current measurement for kinematic viscosity found at engineeringtoolbox.com rho rho [ 1 -3 0 0 0 0 0 ] 1; /* CrossPowerLawCoeffs { nu0 nu0 [ 0 2 -1 0 0 0 0 ] 1e-06; nuInf nuInf [ 0 2 -1 0 0 0 0 ] 1e-06; m m [ 0 0 1 0 0 0 0 ] 1; n n [ 0 0 0 0 0 0 0 ] 0; } BirdCarreauCoeffs { nu0 nu0 [ 0 2 -1 0 0 0 0 ] 0.0142515; nuInf nuInf [ 0 2 -1 0 0 0 0 ] 1e-06; k k [ 0 0 1 0 0 0 0 ] 99.6; n n [ 0 0 0 0 0 0 0 ] 0.1003; } */ } sigma sigma [ 1 0 -2 0 0 0 0 ] 0.00; My forces file is: Code:
forces_object { type forces; functionObjectLibs ( "libforces.so" ); enabled true; outputControl timeStep; outputInterval 1; pName p; UName U; rhoName rhoInf; // Incompressible solver log on; rhoInf 1.0; // Fluid density patches ( cylinder); CofR (0 0 0); pitchAxis (0 0 1); // Gives moment coefficient } Code:
forceCoeffs_object { type forceCoeffs; functionObjectLibs ("libforces.so"); patches (cylinder); pName p; Uname U; rhoName rhoInf; // Reference Density rhoInf 1.0; // Density/1000 log true; // Dump to file -- change to false to not save a file CofR (0.0 0 0); // Centre of rotation liftDir (0 1 0); // Direction of lift coefficient ---> y-direction (transverse to flow) ????? dragDir (1 0 0); // Direction of drag coefficient ---> drag acts in opposite direction to flow (-x) pitchAxis (0 0 1); // Pitch moment axis --> changed from pitchAxis (0 0 1) magUInf 0.4622; // free stream velocity magnitude lRef 6.0; // reference length (cylinder diameter) Aref 1.488; // reference area: lref * zmesh (zmesh is approx. pi*D/76) outputControl timeStep; outputInterval 1; } |
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Tags |
drag coefficient, forces and force coeff., lift coefficent, reference area |
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