Which turbulence model should you use in Simcenter STAR-CCM+?

Start with the flow regime and the result you need. Pressure loss, drag, wall heat transfer and turbulent fluctuations place different demands on the simulation. Separation, buoyancy, rotation and boundary-layer transition also influence the choice. The guide above suggests a model and relevant setup considerations based on your answers.

SST k-ω and near-wall resolution

SST (Menter) K-Omega is a useful starting point for turbulent flows where boundary layers, adverse pressure gradients or separation affect the result. In STAR-CCM+, it is available with Low y+, High y+ and All y+ wall treatments.

All y+ blends the behaviour of Low y+ on fine meshes and High y+ on coarse meshes. It can therefore also be used with a fine mesh intended to resolve the viscous sublayer. For that approach, aim for near-wall cell centres at y+ around 1 or below, and check the achieved Wall Y+ distribution. Accurate wall shear stress and heat transfer also require sufficient prism-layer thickness, resolution along the wall and a mesh sensitivity study.

Realizable k-ε and EB k-ε

Realizable K-Epsilon is a candidate for turbulent internal flows, jets and mixing. The Two-Layer variant uses Two-Layer All y+ Wall Treatment and accommodates both fine and coarse near-wall meshes. EB K-Epsilon is another option documented for internal flows and heat transfer, with particular attention to turbulence near walls.

For turbulent flows dominated by buoyancy, Realizable K-Epsilon Two-Layer offers the Buoyancy Driven (Xu) formulation. Standard K-Epsilon Low-Re, particularly with the Yap correction, is another documented option for natural convection. Assess these choices using the flow regime, density variation, thermal boundary conditions and relevant temperature or heat-transfer data.

Spalart–Allmaras for external aerodynamics

Standard Spalart-Allmaras is a one-equation model suited to predominantly attached aerodynamic boundary layers and mild separation. It can be considered for both subsonic and compressible applications. Choose it according to the flow features and available validation data; select the flow solver and density model to suit the fluid and compressibility of the case.

Reynolds stress models for anisotropic turbulence

Strong swirl and secondary flows can make the directional differences in turbulent stresses important. Reynolds Stress Transport models solve transport equations for the individual stress components and are worth assessing for applications such as cyclone separators. Elliptic Blending RST is one option in STAR-CCM+. Its additional equations increase the computational effort and require attention to convergence.

DDES, IDDES and wall-modelled LES

Consider a scale-resolving approach when the result depends on resolved turbulent fluctuations, for example in a separated wake or a broadband flow-noise calculation. STAR-CCM+ offers DDES and IDDES formulations of SST (Menter) K-Omega Detached Eddy. Wall-modelled LES combines a subgrid-scale model, such as WALE, with near-wall modelling.

These approaches require suitable mesh resolution in the regions where turbulence is resolved, an appropriate time step and enough sampling to establish the required statistics. Their computational cost depends on those choices and the flow being simulated.

When boundary-layer transition matters

If transition from laminar to turbulent flow affects drag, separation or heat transfer, assess a compatible transition model. STAR-CCM+ includes Gamma Transition and Gamma-ReTheta Transition with SST, and SA Gamma Transition with Standard Spalart-Allmaras. The mesh, incoming turbulence and transition mechanism must suit the selected model.

Turbulence modelling for turbomachinery

First establish whether you need mean performance, blade-passage loads or resolved turbulent fluctuations. Choose the motion representation and turbulence approach to match that objective. Check sensitivity to mesh resolution at blade leading edges, in tip gaps and through wakes, using the quantities you need to predict, such as efficiency, leakage flow or wall heat flux.

About this guide

This guide from Volupe covers RANS models, transition modelling and scale-resolving approaches. Model names, compatibility notes and documentation references use the Simcenter STAR-CCM+ 2606 User Guide. Assess the proposed setup through mesh sensitivity, time-step sensitivity where relevant, and comparison with suitable experimental or benchmark data.

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