Final recommendations on turbulence modelling
- Ensure that low numerical and convergence errors have been achieved in turbulent flow simulations. The relevance of turbulence modelling only becomes significant in CFD simulations where other sources of error, in particular the numerical and convergence errors, have been removed or properly controlled. No proper evaluation of the merits of different turbulence models can be made unless the discretisation error of the numerical algorithm is known, and grid sensitivity studies become crucial far all turbulent flow computations.
- Be aware, that there is no universally valid general model of turbulence that is accurate for all classes of flows. It is necessary to calibrate the turbulence model with test data for most applications. Because of its robustness independently of the boundary conditions, the ILES model is a good choice if there isn't any information available to calibrate the turbulence model.
- If possible, examine the effect and sensitivity of results to the turbulence model by changing the turbulence model being used.
- When using a particular turbulence model, check the published literature with regard to the known weaknesses of the model. The weaknesses of the k-ε
model, which is the most commonly used model in industrial applications, are listed in Weaknesses of the k-ε model with chapter, together with same indications of possible palliative actions that might be fruitfully considered.
- Select an appropriate near-wall model. Decide whether to use a wall function method, in which the near-wall region is bridged with wall functions (see Near wall-modelling chapter). This decision will be based on available resources and the requirements for resolution of the boundary layer. The validity of the wall function approach or the use of a low Reynolds number model should be examined for the flow configuration under study. Wall function methods are accurate enough in the presence of separated regions and/or strong three- dimensional flows.
- If the previous recommendations cannot be accomplished, the simplest and more robust zero and one-equations turbulence models can be a good option (see chapter Classes of turbulence models available in Tdyn
).