# Cyclic boundary conditions concerning channel with constant flow rate

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 November 16, 2012, 12:42 Cyclic boundary conditions concerning channel with constant flow rate #1 New Member   Join Date: Oct 2012 Posts: 16 Rep Power: 13 Hi there, I'm trying to simulate a ribbed 2D channel in fully developed flow, by applying cyclic boundary conditions in streamwise direction and using simpleFoam. The case shall be run at a given bulk Reynolds number so that the flow rate must be specified. My blockMeshDict file looks as follows: Code: ```boundary ( inlet { type cyclic; neighbourPatch outlet; faces ( (0 21 22 1) (1 22 23 2) (2 23 24 3) (3 24 25 4) ); } outlet { type cyclic; neighbourPatch inlet; faces ( (16 17 38 37) (17 18 39 38) (18 19 40 39) (19 20 41 40) ); } wall1 { type wall; faces ( (21 0 8 29) ); } wall2 { type wall; faces ( (26 27 6 5) (27 28 7 6) (28 29 8 7) ); } wall3 { type wall; faces ( (26 5 13 34) ); } wall4 { type wall; faces ( (13 14 35 34) (14 15 36 35) (15 16 37 36) ); } wall5 { type wall; faces ( (4 25 33 12) (12 33 41 20) ); } frontAndBack { type empty; faces ( (0 1 9 8) (1 2 10 9) (2 3 11 10) (3 4 12 11) (5 6 14 13) (6 7 15 14) (7 8 16 15) (8 9 17 16) (9 10 18 17) (10 11 19 18) (11 12 20 19) (21 29 30 22) (22 30 31 23) (23 31 32 24) (24 32 33 25) (26 34 35 27) (27 35 36 28) (28 36 37 29) (29 37 38 30) (30 38 39 31) (31 39 40 32) (32 40 41 33) ); } );``` I don't know how to specify the initial and BC? My first attempt for p and U was: Code: ```FoamFile { version 2.0; format ascii; class volScalarField; object p; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // dimensions [0 2 -2 0 0 0 0]; internalField uniform 0; boundaryField { inlet { type cyclic; } outlet { type cyclic; } wall1 { type zeroGradient; } wall2 { type zeroGradient; } wall3 { type zeroGradient; } wall4 { type zeroGradient; } wall5 { type zeroGradient; } frontAndBack { type empty; } }``` Code: ```FoamFile { version 2.0; format ascii; class volVectorField; object U; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // dimensions [0 1 -1 0 0 0 0]; internalField uniform (2.98 0 0); boundaryField { inlet { type cyclic; } outlet { type cyclic; } wall1 { type fixedValue; value uniform (0 0 0); } wall2 { type fixedValue; value uniform (0 0 0); } wall3 { type fixedValue; value uniform (0 0 0); } wall4 { type fixedValue; value uniform (0 0 0); } wall5 { type fixedValue; value uniform (0 0 0); } frontAndBack { type empty; }``` Any help apprechiated! Best regards, Pascal

 November 16, 2012, 13:04 #2 Member   Meindert de Groot Join Date: Jun 2012 Location: Netherlands Posts: 34 Rep Power: 14 Did you have a look at the channelFoam solver? Regarding the initial conditions, I would suggest using the perturbU utility. It generates a perturbed laminar velocity field. You should be able to find more information about it on the forums. The boundary conditions look fine, but be aware that imposing periodic boundary conditions will cause problems in the pressure field if you do not treat the pressure field in a special way (the channelFoam solver takes care of this).