atmAmbientTurbSource

Properties

• The atmAmbientTurbSource applies sources on k and either epsilon or omega to prevent them dropping 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 [m$^2$/s$^2$]

Corrections applied to either of the below, if exist:

epsilon : Turbulent kinetic energy dissipation rate [m$^2$/s$^3$]

omega : Specific dissipation rate [1/s]

Required fields:

k : Turbulent kinetic energy [m$^2$/s$^2$]

and either of:

epsilon : Turbulent kinetic energy dissipation rate [m$^2$/s$^3$]

omega : Specific dissipation rate [1/s]

Model equations

The model expression for epsilon (Heuristically derived from 60, 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 (60, 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 (60, Eq. 3, rhs-term:4):

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

The model expression for k when omega is available (60, 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:

• fvOption
  • cellSetOption

Further information

Tutorials

• atmFlatTerrain
• atmForestStability

Source code

• atmAmbientTurbSource

History: Introduced in version v2006