What Is the Realizable K-Epsilon Model?

One of the more successful recent developments is the realizable K-Epsilon model developed by Shih et al. [39]. This model contains a new transport equation for the turbulent dissipation rate . Also, a critical coefficient of the model, , is expressed as a function of mean flow and turbulence properties, rather than assumed to be constant as in the standard model. This allows the model to satisfy certain mathematical constraints on the normal stresses consistent with the physics of turbulence (realizability). The concept of a variable is also consistent with experimental observations in boundary layers.

The realizable K-Epsilon model is substantially better than the standard K-Epsilon model for many applications, and can generally be relied upon to give answers that are at least as accurate. Both the standard and realizable models have been implemented in STAR-CCM+ with a two-layer approach, which enables them to be used with fine meshes that resolve the viscous sublayer.

Properties

Convection	Selects the convection scheme to be used.
	1st-order	Selects the convection scheme to be used.
	2nd-order	Selects the second-order upwind convection scheme.

Expert Properties

Aside from , which is computed using Eqn. 212, the expert properties are identical to those of the standard K-Epsilon model. Note that the coefficients in the model have different values as specified by Eqn. 214. Note also that the coefficient is computed dynamically from Eqn. 209, but the value specified is used to compute initial or boundary values.

Unless you are thoroughly familiar with the theoretical aspects of this model and the discretization techniques used in STAR-CCM+, we recommend that you not make any changes within the Expert category. The values in that category reflect both the model's design and discretization approaches that have been optimized for accuracy and performance. Tampering with them may diminish the effectiveness of the model.

C2e	The coefficient , see Eqn. 239.
Cmu	The coefficient , see Eqn. 239.
Buoyancy Production of Dissipation	Determines how the coefficient in Eqn. 188 is calculated.
	None	Neglects the term .
	Boundary Layer Orientation	Computes according to Eqn. 196.
	Thermal Stratification	Computes according to Eqn. 195.
Normal Stress Term	Determines whether the full Boussinesq approximation used.
	Ticked	The stress tensor is modeled as and production is computed using Eqn. 189.
	Cleared	The stress tensor is modeled as and production is modeled using the simplified expression .
Sarkar	The coefficient , see Eqn. 198.
Secondary Gradients	Neglect or include the boundary secondary gradients for diffusion and/or the interior secondary gradients at mesh faces.
	On	Include both secondary gradients.
	Off	Exclude both secondary gradients.
	Interior Only	Include the interior secondary gradients only.
	Boundaries Only	Include the boundary secondary gradients only.
Sigma_e	The coefficient , see Eqn. 239.
Sigma_k	The coefficient , see Eqn. 239.
Tdr Minimum	The minimum value that the transported variable is permitted to have. An appropriate value is a small number that is greater than the floating point minimum of the computer.
Tke Minimum	The minimum value that the transported variable is permitted to have. An appropriate value is a small number that is greater than the floating point minimum of the computer.