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how to add a turbulence into a laminar model?

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Old   September 2, 2017, 04:06
Default how to add a turbulence into a laminar model?
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Hi, I have done a simple model of using a velocity at the inlet, to achieve a laminar flow passing through a pipe. The solver is icoFoam. Now I would like to change to a turbulent flow without using any turbulence model (actually I would like to do the DNS). How to modify the boundary conditions to achieve a turbulence?
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Old   September 6, 2017, 10:36
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Hi Matthew,

to turn laminar flow turbulent you have to give some noise as initial condition. To maintain a turbulent flow in a pipe you have to use periodic boundary conditions (and a function object, which imposes a pressure gradient onto your pipe, so that the mean flow rate is steady).
  1. Copy your case to a new directory boxTurbulence, make a simple meshed box slightly bigger than your pipe and use boxTurb:
    1. put this file in your constant directory
    2. run
  2. Map turbulence to pipe:
    1. Make a mapsFieldDict with content:
      patchMap        ( );
      cuttingPatches  ( pipeWall );
    2. Go to your case directory and use boxTurbulence mapFields to map the turbulence from boxTurbulence to your pipe-Mesh:
      mapFields -fields '(U)' [ your path to boxTurbulence directory]
  3. Change the boundary conditions to periodic boundary condtions:
    1. in constant/polyMesh/boundaries the type of your inlet and outlet to cyclic:
      type cyclic;
      inGroups 1(cyclic)
    2. Change also the boundary conditions of the inlet and outlet in U,p,T etc. in the 0 directory:
      type          cyclic;
  4. Based on the Reynolds number you are interested in impose a pressure gradient. Write in constant/fvOptions the following where you have to substitute the Ubar value by the desired mean velocity:
        type              pressureGradientExplicitSource;
        active            on;
        selectionMode   all;
            fieldNames  (U);
            Ubar        ( 1 0 0 );
  5. Run it. If it is not turbulent, play with the values in boxTurbDict.
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Last edited by ano; September 10, 2017 at 08:53.
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Old   November 14, 2018, 07:59
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Jianrui Zeng
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Hello Matthew,

Have you resolved your problem?I am doing similar research on DNS of heated pipe flow.

Any hint or guide is appreciated.

Thank you.
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