# Turbulence models¶

Turbulence modeling is an important issue in many CFD simulations. Virtually all engineering applications are turbulent and hence require a turbulence model. When turbulence is present, it usually dominates all other flow phenomena, which results in the energy dissipation, mixing, heat transfer and drag being increased [1]. Turbulence modeling is the construction and use of a model in order to predict the effects of turbulence.

The Navier–Stokes equations govern the velocity and pressure of a fluid flow. In a turbulent flow, the transport quantities may be decomposed into a mean part and a fluctuating part. The Reynolds-averaged Navier-Stokes (RANS) equation is obtained by averaging the equations which govern the mean flow. There is a closure problem which needs to be done to avoid the velocity fluctuations due to non-linearity of the Navier–Stokes equations [1]. In turbulence modeling we only need to knw the effect of turbulence on the mean flow.

The common turbulence models used in CFD applications are RANS-based models, especially two equation models. SimScale platform makes available the two most commonly used models in industrial and research applications. They are the: