RANS equations and turbulence models

Turbulent flows contain many unsteady eddies covering a range of sizes and time scales. Tdyn includes a module (RANSOL) able to perform turbulent flow simulations by solving the stabilised RANS equations [2]. RANS equations are developed from the time-dependent three-dimensional Navier-Stokes equations that are averaged in such manner, that unsteady structures of small sizes in space and time are eliminated and become expressed by the mean effects on the flow through the so-called Reynolds or turbulent stresses. These stresses have to be interpreted in terms of averaged variables to close the system of equations. This requires the construction of a mathematical model known as a turbulence model.