Tdyn reference manual
- 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.
- 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 Classes of turbulence models available in
Tdyn chapter).