Applying Initial Turbulence for the Realizable k-epsilon Turbulence Model

You can specify the behavior of the Realizable k-epsilon turbulence model at the start of a flow simulation.

This task shows you how to:

Define Initial Turbulence by Specifying k-epsilon
Define Initial Turbulence by Specifying the Intensity - Length Scale
Define Initial Turbulence by Specifying the Intensity - Viscosity Ratio

Before you begin: Specify Realizable k-epsilon as the turbulence model in the fluid physics for the simulation.

Define Initial Turbulence by Specifying k-epsilon

From the Initial Conditions section of the action bar, click Initial Turbulence .
Optional: Enter a descriptive Name.
Select the geometry supports in the model.
An initial turbulence must be applied to one or more fluid regions. You can click the glyph in the model to select the fluid domain.
From the Turbulence specification options, select k-epsilon.
Specify the Turbulent kinetic energy, $k$ . This value must be greater than zero.
Specify the Dissipation rate, $ω$ . This value must be greater than zero.
Click OK.

Define Initial Turbulence by Specifying the Intensity - Length Scale

From the Initial Conditions section of the action bar, click Initial Turbulence .
Optional: Enter a descriptive Name.
Select the geometry supports in the model.
An initial turbulence must be applied to one or more fluid regions. You can click the glyph in the model to select the fluid domain.
From the Turbulence specification options, select Intensity - Length scale.
Specify the Turbulence intensity, which is 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.
Specify the Turbulence length scale, which defines 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).
Specify the Velocity scale, which describes the characteristic velocity of the problem. This value is required to avoid cases where the initial velocity field is zero.
Click OK.

Define Initial Turbulence by Specifying the Intensity - Viscosity Ratio

From the Initial Conditions section of the action bar, click Initial Turbulence .
Optional: Enter a descriptive Name.
Select the geometry supports in the model.
An initial turbulence must be applied to one or more fluid regions. You can click the glyph in the model to select the fluid domain.
From the Turbulence specification options, select Intensity - Viscosity scale.
Specify the Turbulence intensity, which is 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 $k = \frac{3}{2 u^{'}}$ . Select the Turbulence Specification. 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.
Specify the Turbulence viscosity ratio, which defines the characteristic velocity of the problem. This value is required to avoid cases where the initial velocity field is zero.
Specify the Velocity scale, which describes the characteristic velocity of the problem. This value is required to avoid cases where the initial velocity field is zero.
Click OK.