[zhangxc0223]

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?

[ano]

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 https://github.com/OpenFOAM/OpenFOAM...nt/boxTurbDict in your constant directory
   2. run

      boxTurb

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:
   

   pressureGradient
   {
       type              pressureGradientExplicitSource;
       active            on;
       selectionMode   all;
   
       pressureGradientExplicitSourceCoeffs
       {
           fieldNames  (U);
           Ubar        ( 1 0 0 );
       }
   }

5. Run it. If it is not turbulent, play with the values in boxTurbDict.

[calf.Z]

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.