The term laminar refers to a well-ordered flow, free of macroscopic, non-repeating fluctuations. Laminar flows occur in nature when the Reynolds number (the ratio of viscous to inertial forces) is low enough that transition to turbulence does not occur.
In computational simulations, numerical instabilities can arise from simulating laminar flows at Reynolds numbers that are too large, and these will impede convergence if a steady solution is sought. Therefore, laminar flow simulation is appropriate if it is known a priori that the Reynolds number of the problem is sufficiently low.
Turbulence Response Model
The Turbulence Response Model predicts velocity fluctuations in the dispersed phase using algebraic correlations to the velocity fluctuations in the continuous phase
Standard K-Epsilon Model (with high-y+ wall treatment)
The standard K-Epsilon Model is a de facto standard version of the two-equation model that involves transport equations for the turbulent kinetic energy and its dissipation rate. Some additional terms have been added to the model in STAR-CCM+ to account for effects such as buoyancy and compressibility. An optional non-linear constitutive relation is also provided.
Standard Two-Layer K-Epsilon Model (with two-layer wall treatment)
The standard two-Layer K-Epsilon Model combines the standard K-Epsilon Model with the two-layer approach. The coefficients in the models are identical, but model gains the added flexibility of an all y+ wall treatment.
Realizable K-Epsilon Model (with two-layer wall treatment)
The realizable K-Epsilon Model contains a new transport equation for the turbulent dissipation rate ε. Also, a critical coefficient of the model, C, 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 C 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.