## 14.3. Turbulence

The following topics will be discussed:

- Zero Equation Model

- Two-Equation Models

- Reynolds Stress Model

### Zero Equation Model

The use of this model incurs a small increase in CPU time and memory requirements compared to laminar flow.

### Two-Equation Models

Two additional scalar equations are solved when using two-equation turbulence models. The SST model has a slight additional cost over other two-equation models because a wall-scale equation is also solved.

Consider the case of single-phase, single-component laminar flow in which the U-Mom, V-Mom, W-Mom, and P-Mass equations are solved. Expect a CPU cost increase on the order of 50% by the addition of a two-equation turbulence model. Memory requirement increases are small.

### Reynolds Stress Model

This model adds six scalar equations for each of the Reynolds Stresses as well as the Eddy Dissipation equation. It is approximately 2.5 times more expensive than the two-equation turbulence models.

Consider the case of single phase, single component laminar flow in which the U-Mom, V-Mom, W-Mom, and P-Mass equations are solved. Expect a CPU cost increase on the order of 120% by the addition of a Reynolds Stress turbulence model. Memory requirement increases are small.

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