Next in the workflow is the definition of the fluid transport models using the Transport workflow item. The Editor panels for the two items under the Transport node, Turbulence and Fluid Properties, are described below. The Transport Editor panel provides settings for Fluid Properties. The parameters on this panel are reference properties used to calculate the turbulent fluid properties. These fluid property correlations are explained in the following paragraphs and also described in the tool tips. The Body Acceleration terms in the fluid transport model can be used to specify acceleration due to gravity. The equations that use these properties are defined in the Ansys Forte Theory Manual.
Prandtl Number: Prandtl number of the laminar fluid flow, defined as
(3–2)
where
is the specific heat at constant pressure, 
is dynamic viscosity of laminar flow, and 
is thermal conductivity of laminar flow. Note that 
is only used in the wall heat transfer model. Recip. Turb. Prandtl Number and Recip. Turb Schmidt Number: The reciprocals of turbulent Prandtl Number and turbulent Schmidt Number. These two parameters are used to convert dynamic viscosity into thermal diffusivity and mass diffusivity, respectively, for turbulent flow transport calculation. The turbulent Prandtl Number and turbulent Schmidt Number are defined as:
(3–3)
(3–4)
Where
is turbulent thermal diffusivity, 
is turbulent mass diffusivity, 
is turbulent kinematic viscosity. In Ansys Forte, the effective dynamic
viscosity for turbulent flows, 
, is the sum of two terms, a laminar term and a turbulent term, that is, 
(3–5)
where
and 
are turbulent kinetic energy and its dissipation rate, respectively, and
is a constant in the turbulence model. In turbulent flow simulations, the
laminar term 
is typically much smaller than the turbulent term, and hence the effective
dynamic viscosity is simply noted as 
. Air Mu Coef. 1 (
) and Air Mu Coef. 2 (
): Coefficients in the Sutherland’s formula for calculating laminar
viscosity of the fluid as a function of temperature: 
(3–6)
Air Lambda Coef. 1 (
) and Air Lambda Coef. 2 (
): Coefficients in the correlation for calculating laminar thermal
conductivity of the flow as a function of temperature: 
(3–7)
Note that
is only used in spray vaporization model for computing the thermal
conductivity of air.
Note: Ansys recommends accepting the defaults under Fluid Properties for most engine cases.
Transport Total Energy: For high-speed flow simulations, it may be desirable to transport the total energy of the fluid instead of transporting the internal energy alone in the energy transport equation formulation. The total energy includes both internal energy and kinetic energy. By default, only internal energy is transported in the energy conservation equation. Such a treatment is appropriate for low-speed flows because the kinetic energy is small compared to the internal energy. For high-speed flows, such as supersonic flows, the kinetic energy may no longer be negligible, and you can check the Transport Total Energy box to transport total energy in the energy equation.
Use the Turbulence Editor panel to select among choices for the Turbulence Model: RANS (Reynolds-Averaged Navier-Stokes) or LES (Large-Eddy Simulation) models. For the RANS models, options of RNG k-epsilon or k-epsilon are offered. For LES models, the options of Smagorinsky or Dynamic Structure model are available. Select no model for a laminar flow simulation.
For a simulation with the RANS approach, the default choice of RNG (Re-Normalization Group) k-epsilon is recommended, although a standard k-epsilon model may also be selected.
Note: Ansys recommends using the RNG-k-epsilon model for engine cases and for spray-chamber cases. The spray models have many years of calibration to this model and are unlikely to work as well with the k-epsilon model. The RNG-k-epsilon model should also be a better model for engine combustion. The standard model is included for research purposes or for use with problems such as pure air flow, for example, where it might be more appropriate.
For a simulation with the LES approach, the Dynamic Structure model is recommended. The Smagorinsky model is included due to its simplicity and historical importance. However, it is considered as over-dissipative and less accurate compared to the Dynamic Structure model.
For the turbulence model selected, there are a number of model parameters displayed. However, the default values are recommended. Details on how the turbulence equations use these parameters are included in the Ansys Forte Theory Manual.