Turbulence — Best Practices

Note

In construction.

Summary of turbulence model compatibility in TrioCFD

Model	VEF	VDF	PolyMAC
\(k\)- \(\omega\) (Pb_Multiphase)		✓	✓
\(k\)- \(\omega\) SST (Pb_hydraulique_turbulent)	✓	✓
\(k\)- \(\varepsilon\)	✓	✓

For the historical record: at first, there was only a \(k\)- \(\varepsilon\) model in TrioCFD. At some point, the multiphase framework arrived with the PolyMAC discretisation. Someone needed turbulence, so a first \(k\)- \(\omega\) model was made in PolyMAC. Then a need was expressed to have a \(k\)- \(\omega\) SST model in the historical Pb_hydraulique_turbulent framework. A first implementation was started in VDF but was quickly stopped to switch to the VEF discretisation. Then the VDF discretisation was made available with Pb_Multiphase, so the \(k\)- \(\omega\) model was extended to it in the Pb_Multiphase framework. At some point someone needed to use the \(k\)- \(\omega\) model in Pb_hydraulique_turbulent with the VDF discretisation. So rather than finishing the previous implementation and validating it, they chose to minimise the validation work and instead allowed using the \(k\)- \(\omega\) Pb_Multiphase version with Pb_hydraulique_turbulent. Later, new work was carried on the hybrid RANS/LES method. The main framework was the VEF discretisation (so Pb_hydraulique_turbulent) but some validation was needed using VDF. As the code structure is different between Pb_hydraulique_turbulent and Pb_Multiphase, it was decided to finish the VDF version of the \(k\)- \(\omega\) SST in Pb_hydraulique_turbulent.

As of 2025, a complete redesign of the turbulence-related code is under consideration to reduce code duplication and to allow for an easier extension. But workforce is limited and the project is huge.

Recommendations

The most used model in TrioCFD was historically the \(k\)- \(\varepsilon\) one with a wall function. This is robust and fast. Some low-Reynolds models are available but not yet fully validated. The \(k\)- \(\omega\) SST model being the most widely used one in the literature, we recommend using it.

Further reading

Websites:

• The turbulence modeling group

For the hasty readers:

• E. Goncalves (2017), Lessons on turbulence modeling (in French) — link

For the patient readers:

• R. Schiestel (2008), Modeling and Simulation of Turbulent Flows. It provides numerous and deep details on the modeling process.