turbulent flow simulation. The next section gives you an overview of each of the interfaces to help you choose.

The Non-Isothermal Flow Interface Options

Several of the interfaces vary only by one or two default settings, which are selected during Model Wizard selection, or from a check box or drop-down list on the individual interfaces. The interfaces in the Non-Isothermal Flow and Conjugate Heat Transfer branches relate to each other based on selections made from the drop-down lists in the Settings window (Figure 12-1).

N O N - I S O T H E R M A L F L O W , L A M I N A R F L O W

The Non-Isothermal Flow, Laminar Flow Interface () is used primarily to model slow-moving flow in environments where energy transport is also an important part of the system and application, and must coupled or connected to the fluid-flow in some way. Processes where natural convection are an important component are classic areas for such modeling. The interface solves the Navier-Stokes equations together with an energy balance assuming heat flux through convection and conduction. The density term is assumed to be affected by temperature and flow is always assumed to be compressible. Stokes’ law (creeping flow) can be activated from the Non-Isothermal Flow, Laminar Flow interface if wanted.

N O N - I S O T H E R M A L F L O W , T U R B U L E N T F L O W

The Turbulent Flow, k- and Turbulent Flow Low Re k- Interfaces, The Turbulent Flow, Spalart-Allmaras Interface, and The Turbulent Flow, k- Interface () model flows that are relatively fast-moving and/or geometries that change significantly to induce disorder, vortices and eddies. Once again, the interfaces are also set up assuming that energy transport is also an important part of the system and application, and must be coupled or connected to the fluid-flow in some way. Process or component cooling are classic examples. For this reason, the interface includes added functionality for calculating the added dispersion of heat transfer due to turbulence. This is represented by one of the Kays-Crawford or Extended Kays-Crawford Turbulence heat transport models, or by including your own turbulent Prandtl number.

In addition to the properties for the different turbulence models mentioned in Theory for the Turbulent Flow Interfaces, an additional important aspect is that the reward in terms of accuracy for using low-Reynolds number models is even higher in non-isothermal flow simulations. The reason is that the local equilibrium assumption

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on which the wall functions rely is seldom fulfilled when there are temperature gradients present.

This is particularly relevant for applications in non-isothermal flow where the heat flux

at solid-liquid interfaces is important to the final solution.

Figure 12-1: The Settings window for the Non-Isothermal Flow, Turbulent Flow interface. You can model laminar and turbulent flow, Stokes flow, and conjugate heat transfer. Combinations are also possible.

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