atmAmbientTurbSource

Table of Contents

Properties

  • The atmAmbientTurbSource applies sources on k and either epsilon or omega to prevent them droping below a specified ambient value for atmospheric boundary layer modelling.
  • Such adjustment reportedly increases numerical stability for very stable atmospheric stability conditions, and prevents nonphysical oscillations in regions of low shear at higher altitudes.
  • The atmAmbientTurbSource can be applied on epsilon or omega based RAS turbulence models.
  • The atmAmbientTurbSource inherits the traits of the fvOption, and cellSetOption.

Corrections applied to: 

k         | Turbulent kinetic energy                  [m2/s2]

Corrections applied to either of the below, if exist: 

epsilon   | Turbulent kinetic energy dissipation rate [m2/s3]
omega     | Specific dissipation rate                 [1/s]

Required fields: 

k             | Turbulent kinetic energy                      [m2/s2]
epsilon/omega | Dissipation rate OR Specific dissipation rate [m2/s3]/[1/s]

Model equations

The model expression for epsilon (Heuristically derived from ([64], Eq. 4, rhs-term:5)):

\[ S_p = \alpha \rho C_2 \frac{\epsilon_{amb}^2}{k_{amb} \epsilon_o} \epsilon \]

The model expression for omega ([64], Eq. 4, rhs-term:5):

\[ S_p = \alpha \rho C_\mu \beta \frac{\omega^2_{amb}}{\omega_o} \omega \]

The model expression for k when epsilon is available (Heuristically derived from ([64], Eq. 3, rhs-term:4)):

\[ S_p = \alpha \rho \frac{\epsilon_{amb}}{k_o} k \]

The model expression for k when omega is available ([64], Eq. 3, rhs-term:4):

\[ S_p = \alpha \rho C_\mu \frac{\omega_{amb} k_{amb}}{k_o} k \]

where

\( S_p \) = Source term without boundary conditions
\( \epsilon \) = Turbulent kinetic energy dissipation rate (Current iteration) [m2/s3]
\( \omega \) = Specific dissipation rate (Current iteration) [1/s]
\( k \) = Turbulent kinetic energy (Current iteration) [m2/s2]
\( \epsilon_{amb} \) = Ambient epsilon value [m2/s3]
\( \omega_{amb} \) = Ambient omega value [1/s]
\( k_{amb} \) = Ambient k value [m2/s2]
\( \epsilon_o \) = Previous-iteration epsilon [m2/s3]
\( \omega_o \) = Previous-iteration omega [1/s]
\( k_o \) = Previous-iteration k [m2/s2]
\( C_2 \) = Model constant [-]
\( C_\mu \) = Empirical model constant [-]
\( \beta \) = Model constant [-]
\( \alpha \) = Phase fraction in multiphase computations, otherwise equals to 1
\( \rho \) = Fluid density in compressible computations, otherwise equals to 1

Usage

Example of the fvOptions specification using constant/fvOptions file: 

atmAmbientTurbSource1
{
    // Mandatory entries (unmodifiable)
    type                  atmAmbientTurbSource;

    atmAmbientTurbSourceCoeffs
    {
        // Mandatory (inherited) entries (unmodifiable)
        selectionMode    all;

        // Mandatory entries (unmodifiable)
        kAmb              0.0;

        // Optional entries (unmodifiable)
        rho               rho;
        epsilonAmb        0.0;
        omegaAmb          0.0;
    }

    // Optional (inherited) entries
    ...
}

where the entries mean:

Property Description Type Required Default
type Type name: atmAmbientTurbSource word yes -
kAmb Ambient value for k scalar yes -
rho Name of density field word no rho
epsilonAmb Ambient value for epsilon scalar no 0.0
omegaAmb Ambient value for omega scalar no 0.0

The inherited entries are elaborated in:

Further information

Tutorials

Source code

History

  • Introduced in version v2006