# K-Omega-Epsilon BCs for suction inlet

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 March 27, 2018, 18:28 K-Omega-Epsilon BCs for suction inlet #1 New Member   Romit Join Date: Mar 2018 Location: Stillwater, OK, USA Posts: 2 Rep Power: 0 Hello everyone. I have a question about RAS turbulence boundary conditions related to a suction inlet (i.e. uniform flow velocity out of the domain). While my k omega SST turbulence model converges, my k epsilon implementation blows up (though this might be because this isn't really a free shear layer problem). My y+ is uniform (for now) at about 20. After shadowing these forums extensively, it seemed that k omega SST with the omegaWallFunction, the nutUSpaldingWallFunction, the kqRWallFunction takes care of the wall boundary conditions. My question is related to the suction inlet (which I hadn't thought of really). I have been using the usual CFD online tool (https://www.cfd-online.com/Tools/turbulence.php) to calculate my k, omega and epsilon assuming my turbulence length scale to be 0.07 the hydraulic diameter and specifying them through turbulentIntensityKineticEnergyInlet (for k), fixedValue (for omega), turbulentMixingLengthDissipationRateInlet (for epsilon). However this link (https://www.openfoam.com/documentati...alarField.html) says "In the event of reverse flow, a zero-gradient condition is applied" for omega. Now technically in my suction inlet, a reverse flow IS happening. I'm at a loss here - what exactly do I specify for my inlet and outlet BCs for k, omega, epsilon. I have my boundary conditions added here. U Code: ```internalField uniform 10; boundaryField { walls { type kqRWallFunction; value \$internalField; } outlets { type zeroGradient; } inlet { type turbulentIntensityKineticEnergyInlet; intensity 0.02; value uniform 0.00015; } }``` P Code: ```dimensions [0 2 -2 0 0 0 0]; internalField uniform 0; boundaryField { inlet { type zeroGradient; } outlets { type totalPressure; p0 uniform 0.0; gamma 0.0; value \$internalField; } walls { type zeroGradient; } }``` nut Code: ```dimensions [0 2 -1 0 0 0 0]; internalField uniform 0.14; boundaryField { inlet { type freestream; freestreamValue uniform 0.14; } outlets { type freestream; freestreamValue uniform 0.14; } walls { type nutUSpaldingWallFunction; value uniform 0; } }``` k Code: ```dimensions [0 2 -2 0 0 0 0]; internalField uniform 10; boundaryField { walls { type kqRWallFunction; value \$internalField; } outlets { type zeroGradient; } inlet { type turbulentIntensityKineticEnergyInlet; intensity 0.02; value uniform 0.00015; } }``` epsilon Code: ```dimensions [0 2 -3 0 0 0 0]; internalField uniform 100; boundaryField { walls { type epsilonWallFunction; value \$internalField; } outlets { type zeroGradient; } inlet { type turbulentMixingLengthDissipationRateInlet; mixingLength 0.0378; value uniform 200; // placeholder } }``` omega Code: ```dimensions [0 0 -1 0 0 0 0]; internalField uniform 1000; boundaryField { walls { type omegaWallFunction; Cmu 0.09; kappa 0.41; E 9.8; value \$internalField; } inlet { type fixedValue; value uniform 0.324; } outlets { type zeroGradient; } }``` Thanks for reading! If you need anymore information, feel free to ask.

 Tags boundary conditions, k omega sst, rasmodel