Choose between different turbulence models and options for RANS and DES simulations in Fluid Physics under the Physics subsection of the control panel. If you do not see the options below, first verify that the correct Viscous Model is set.

If you are running a RANS or DES simulation, Luminary Cloud currently supports two turbulence models:

Once you've selected a turbulence model, fine tune it using the Turbulence Model Constants dropdown. In this menu, Default will select the model’s standard constants, and Custom will allow you to adjust each of these constants below.

For Spalart-Allmaras and SST, you can turn on QCR:

For Spalart-Allmaras only:

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Detached Eddy Simulation (DES) combines the advantages of both RANS and LES formulas. It uses RANS near walls where flow is usually more predictable and less turbulent, and switches to LES in the main flow regions where turbulence is more dominant.

When using DES, you will also be able to set the DES Formulation after setting up the model constants. The options available include:

If you are running an LES simulation, you can select the Sub-Grid Scale Model. The options available are:

For all of these you can adjust each model's single coefficient.

For RANS, DES, and LES, you can modify the Turbulent Prandtl Number to adjust how quickly heat is transferred from the walls into the fluid. A lower number implies faster heat transfer. Note that the default value used by Luminary is 0.85.

For RANS simulations, you can use transition models to simulate cases in which the flow changes in nature from laminar to turbulent as it moves through the domain.

The options available are:

For the two- and three-equation models, you'll need to define a Free Stream Turbulence Intensity value. This is a measure of turbulence present in the flow of a fluid before it hits an object or surface, with higher values indicating more turbulence and lower values indicating smoother flow.

‍For all three transition models, choose whether to turn Crossflow Treatment on or off. Crossflow can create complex flow patterns, mixing, or interference that may impact performance, efficiency, or safety. Crossflow Treatment aims to optimize these interactions to reduce undesirable effects like turbulence or pressure loss, enhance heat transfer, or improve overall efficiency.

After running a simulation with a transition model, you can view additional solution residuals. Go to Outputs > Solution Residuals in the control panel. Under Include, you will see Turbulence Intermittency (one-, two-, and three-equation models), Momentum-Thickness Reynolds Number (two-equation model only), and Amplification Factor (three-equation model only) as options.

One-equation transition models typically solve a transport equation for the intermittency γ. The gamma-2015 model (γ-2015) uses local algebraic relations to compute this quantity, removing the need for solving the transport equation. This model is simple and Galilean invariant, making it a good candidate for solving both natural and forced transitional flows where relative motion occurs.

Two-equation transition models typically solve one transport equation for the intermittency γ and one for another quantity related to the actual transition. The gamma-Re_theta-2009 model (γ-Reθt-2009) uses two transport equations, one for the intermittency γ and one for the transition Reynolds number based on the momentum thickness. This model is not Galilean invariant due to its dependency on the velocity vector, making its accuracy for solving transitional flows where relative motion occurs case-dependent. We recommend using this model for both natural and forced laminar-turbulent flow simulations.

The Amplification Factor Transport model (AFT-2019) uses two transport equations: intermittency γ and amplification factor ñ. This model is a good candidate for modeling natural transitions from laminar to turbulent flow in aerodynamic applications.

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