Initial Turbulence Options

The tables below describes the options available in an initial turbulence condition. Different parameters are available for each turbulence model (chosen in the physics definition).

This page discusses:

Spalart-Allmaras Options
Realizable K-Epsilon Options
SST K-Omega Options

Spalart-Allmaras Options

The following turbulence Specification options are available for the Spalart-Allmaras turbulence model:

Viscosity ratio: Define turbulence by specifying the eddy viscosity ratio.
Intensity - Length scale: Define turbulence by specifying the turbulence intensity, characteristic length scale, and velocity scale.
Turbulent viscosity: Define turbulence by specifying the kinematic eddy viscosity.

Select one of them, then complete the initial turbulence definition by specifying the other related options below.

Viscosity Ratio Options


Turbulent viscosity ratio	Eddy viscosity ratio; the ratio of eddy viscosity to molecular dynamic viscosity.

Intensity - Length Scale Options


Turbulence intensity	The ratio between the characteristic turbulent velocity scale and the characteristic velocity scale of the flow $(\frac{u^{'}}{U})$ . The turbulent velocity scale is related to the turbulent kinetic energy ( $k$ ) by $k = \frac{3}{2 u^{'}}$ . Therefore, the turbulence intensity indicates the level of turbulent kinetic energy present as a proportion of the characteristic velocity encountered in the flow. Typical values range from 0.05 to 0.2.
Turbulence length scale	The characteristic length scale of the turbulent structures or eddies encountered in turbulent flows. This value indicates the size of the most energetic turbulent scales of the flow. It is usually proportional to the size of recirculation zones, boundary layers, or large vertical structures. The turbulent length scale you enter cannot be larger than the size of the model; it should usually be a small fraction of a characteristic dimension of the model (such as the flow inlet diameter).
Velocity scale	Characteristic velocity of the problem. This value is required to avoid cases where the initial velocity field is zero.

Turbulent Viscosity Options


Kinematic eddy viscosity	The kinematic eddy viscosity, $\tilde{v}$ . This must be a nonzero value and should be roughly three to five times the kinematic viscosity. The kinematic viscosity is the ratio of the fluid viscosity and density ( $ν = η / ρ$ ).

Realizable K-Epsilon Options

The following turbulence Specification options are available for the Realizable K-Epsilon turbulence model:

Intensity - Viscosity ratio: Define turbulence by specifying the turbulence intensity, turbulence viscosity ratio, and velocity scale.
Intensity - Length scale: Define turbulence by specifying the turbulence intensity, characteristic length scale, and velocity scale.
K-epsilon: Define turbulence by specifying the turbulent kinetic energy and dissipation rate.

Select one of them, then complete the initial turbulence definition by specifying the other related options below.

Intensity - Viscosity Ratio Options


Turbulence intensity	The ratio between the characteristic turbulent velocity scale and the characteristic velocity scale of the flow $(\frac{u^{'}}{U})$ . The turbulent velocity scale is related to the turbulent kinetic energy ( $k$ ) by $k = \frac{3}{2 u^{'}}$ . Therefore, the turbulence intensity indicates the level of turbulent kinetic energy present as a proportion of the characteristic velocity encountered in the flow. Typical values range from 0.05 to 0.2.
Turbulence viscosity ratio	Eddy viscosity ratio; the ratio of eddy viscosity to molecular dynamic viscosity.
Velocity scale	Characteristic velocity of the problem. This value is required to avoid cases where the initial velocity field is zero.

Intensity - Length Scale Options


Turbulence intensity	The ratio between the characteristic turbulent velocity scale and the characteristic velocity scale of the flow $(\frac{u^{'}}{U})$ . The turbulent velocity scale is related to the turbulent kinetic energy ( $k$ ) by $k = \frac{3}{2 u^{'}}$ . Therefore, the turbulence intensity indicates the level of turbulent kinetic energy present as a proportion of the characteristic velocity encountered in the flow. Typical values range from 0.05 to 0.2.
Turbulence length scale	The characteristic length scale of the turbulent structures or eddies encountered in turbulent flows. This value indicates the size of the most energetic turbulent scales of the flow. It is usually proportional to the size of recirculation zones, boundary layers, or large vertical structures. The turbulent length scale you enter cannot be larger than the size of the model; it should usually be a small fraction of a characteristic dimension of the model (such as the flow inlet diameter).
Velocity scale	Characteristic velocity of the problem. This value is required to avoid cases where the initial velocity field is zero.

K-Epsilon Options


Turbulent kinetic energy	The turbulent kinetic energy, $k$ . This value must be greater than zero.
Dissipation rate	The dissipation rate of the turbulent kinetic energy, $ε$ . This value must be greater than zero.

SST K-Omega Options

The following turbulence Specification options are available for the SST K-Omega turbulence model:

Intensity - Viscosity ratio: Define turbulence by specifying the turbulence intensity, viscosity ratio, and velocity scale.
Intensity - Length scale: Define turbulence by specifying the turbulence intensity, length scale, and velocity scale.
K-Omega: Define turbulence by specifying the turbulent kinetic energy and energy dissipation rate.

Select one of them, then complete the initial turbulence definition by specifying the other related options below.


Specification	Intensity - Viscosity ratio: Define turbulence by specifying the turbulence intensity, viscosity ratio, and velocity scale. Intensity - Length scale: Define turbulence by specifying the turbulence intensity, length scale, and velocity scale. K-Omega: Define turbulence by specifying the turbulent kinetic energy and energy dissipation rate.

Intensity - Viscosity Ratio Options


Turbulence intensity	The ratio between the characteristic turbulent velocity scale and the characteristic velocity scale of the flow $(\frac{u^{'}}{U})$ . The turbulent velocity scale is related to the turbulent kinetic energy ( $k$ ) by $k = \frac{3}{2 u^{'}}$ . Therefore, the turbulence intensity indicates the level of turbulent kinetic energy present as a proportion of the characteristic velocity encountered in the flow. Typical values range from 0.05 to 0.2.
Turbulence viscosity ratio	Eddy viscosity ratio; the ratio of eddy viscosity to molecular dynamic viscosity.
Velocity scale	Characteristic velocity of the problem. This value is required to avoid cases where the initial velocity field is zero.

Intensity - Length Scale Options


Turbulence intensity	The ratio between the characteristic turbulent velocity scale and the characteristic velocity scale of the flow $(\frac{u^{'}}{U})$ . The turbulent velocity scale is related to the turbulent kinetic energy ( $k$ ) by $k = \frac{3}{2 u^{'}}$ . Therefore, the turbulence intensity indicates the level of turbulent kinetic energy present as a proportion of the characteristic velocity encountered in the flow. Typical values range from 0.05 to 0.2.
Turbulence length scale	The characteristic length scale of the turbulent structures or eddies encountered in turbulent flows. This value indicates the size of the most energetic turbulent scales of the flow. It is usually proportional to the size of recirculation zones, boundary layers, or large vertical structures. The turbulent length scale you enter cannot be larger than the size of the model; it should usually be a small fraction of a characteristic dimension of the model (such as the flow inlet diameter).
Velocity scale	Characteristic velocity of the problem. This value is required to avoid cases where the initial velocity field is zero.

K-Omega Options


Turbulent kinetic energy	The turbulent kinetic energy, $k$ . This value must be greater than zero.
Omega	The specific energy dissipation rate, $ω$ . This value must be greater than zero.