diff --git a/_docs_v7/Markers-and-BC.md b/_docs_v7/Markers-and-BC.md index 9f291c37..8678a960 100755 --- a/_docs_v7/Markers-and-BC.md +++ b/_docs_v7/Markers-and-BC.md @@ -13,6 +13,8 @@ The term *Marker* refers to a named entity in your mesh file. Boundary condition - [Heat Transfer or Convection (no-slip) Wall](#heat-transfer-or-convection-no-slip-wall) - [Isothermal (no-slip) Wall](#isothermal-no-slip-wall) - [Farfield Boundary Condition](#farfield-boundary-condition) +- [Turbulence Boundary Condition](#turbulence-boundary-condition) + - [Wall functions](#wall-functions) - [Inlet Boundary Condition](#inlet-boundary-condition) - [Total Conditions](#total-conditions) - [Mass Flow Inlet](#mass-flow-inlet) @@ -121,6 +123,40 @@ A marker can be defined as a Farfield boundary by addings its name to the `MARKE MARKER_FAR= (farfield) ``` +## Turbulence Boundary Condition ## + +| Solver | Version | +| --- | --- | +| `RANS`, `INC_RANS`, | 7.3.0 | + +The turbulence boundary conditions do not have a `MARKER_` keyword but can instead be set for inlet and freestream boundaries using the keywords: + +For the SA turbulence model: +``` +FREESTREAM_NU_FACTOR= 3 +``` + +For the SST turbulence model: +``` +FREESTREAM_TURBULENCEINTENSITY= 0.05 +FREESTREAM_TURB2LAMVISCRATIO= 10 +``` + +### Wall functions ### +Accurately resolving the turbulence close to walls requires very fine meshes and can be quite expensive. When the vertices of the first cell neighboring the wall have on average a normalized distance $$y^+ >1$$, wall functions can be used. For example to activate wall functions on the markers `wall1` and `wall2`, we write: +``` +MARKER_WALL_FUNCTIONS=(wall1,STANDARD_WALL_FUNCTION,wall2,STANDARD_WALL_FUNCTION) +``` +The wall functions will now be used automatically. all functions have 5 additional expert parameters: +``` +WALLMODEL_KAPPA= 0.41 +WALLMODEL_B= 5.5 +WALLMODEL_MINYPLUS= 5.0 +WALLMODEL_MAXITER= 200 +WALLMODEL_RELFAC= 0.5 +``` +The constant `WALLMODEL_KAPPA` is the von Karman constant, and `WALLMODEL_B` is an additional constant describing the universal 'law of the wall'. The constants are supposed to be universal, and do not change. The setting `WALLMODEL_MINYPLUS= 5` will activate the wall model only when the local value of $$y^+$$ is higher than the value given (default: 5). Note that in principle, this implementation is valid for any $$y^+ < 100-500$$ and will also work correctly for very small values of $$y^+$$. the upper limit that can be used depends on (and increases with) the Reynolds number. The universal law of the wall is an implicit function and a Newton iterator is used to determine $$u^+(y^+)$$. The maximum number of iterations can be set by `WALLMODEL_MAXITER` and the relaxation factor can be set with `WALLMODEL_RELFAC`. When the Newton solver does not converge within the maximum number of iterations given, a warning message will appear during the computation. When these warning messages do not disappear, you might consider increasing `WALLMODEL_MAXITER` or decreasing `WALLMODEL_RELFAC`. + ## Inlet Boundary Condition ## Inlet boundary conditions are set using the option `MARKER_INLET`.