Convective Heat Transfer Analysis
The convective heat transfer analysis could be used to run simulations in which temperature changes in the fluid lead to density changes. Such changes in density cause the fluid to circulate under the influence of gravity.
In the following, convective heat transfer simulation setup is discussed.
Radiation
SimScale also allows for the inclusion of radiation in your Convective Heat Transfer simulation. A Diffuse View Factors model is used, which calculates the radiative heat exchange between all the surfaces of the given domain.
Turbulence model
A turbulence model should be chosen in accordance to the flow regime. In a Laminar flow, associated with low Reynolds numbers, viscous effects dominate the flow and turbulence can be neglected. This flow regime is characterized by regular flow layers.
On the other hand, a turbulent flow is characterized by chaotic and irregular patterns that are associated with Reynolds numbers. In order to simulate a turbulent fluid flow an appropriate turbulence model should be chosen. Currently, these models are supported:
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- Reynolds-averaged Navier–Stokes (RANS)
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- k-Epsilon
- kOmega-SST
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- Large eddy simulation (LES)
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- Smagorinsky
- Spalart-Allmaras
Time dependency
There are two variants of simulation: Steady-state and Transient flow. In order to account for time-dependent effects, consider a transient simulation. If you are only interested in the converged steady state solution, where the flow condition does not change over time, consider a steady-state simulation. Steady-state simulations are computationally less demanding.
Solver
Depending on the chosen turbulence and time-dependency, different solvers are available. Each combination of choices corresponds to one of the OpenFOAM® solvers. The complete list of available solvers are presented in table below.
| turbulence model | Time dependency | OpenFOAM® solver | Boussinesq approximation ON |
|---|---|---|---|
| Laminar | Transient | buoyantPimpleFoam | buoyantBoussinesqPimpleFoam |
| Steady-state | buoyantSimpleFoam | buoyantBoussinesqSimpleFoam | |
| RANS | Transient | buoyantPimpleFoam | buoyantBoussinesqPimpleFoam |
| Steady-state | buoyantSimpleFoam | buoyantBoussinesqSimpleFoam | |
| LES | Transient | buoyantPimpleFoam | buoyantBoussinesqPimpleFoam |
| Steady-state | buoyantSimpleFoam | buoyantBoussinesqSimpleFoam |
Important
Boussinesq approximation works for incompressible fluids, and for gases if temperature differences are small.
Domain
In order to perform a convective heat transfer simulation on a given domain you have to discretize your geometry by creating a mesh. Details of CAD handling and Meshing are described in the Pre-processing section.
After a mesh is assigned to the simulation, it is possible to use domain-related entities associated with the mesh in setting up the simulation. Additionally, one can view the mesh or define new entities, e.g. a Topological Entity Set, to facilitate the simulation setup process. Details of each step are described in the following sections:
Model
For convective heat transfer simulations, gravity and preference pressure should be set. Furthermore, the thermal properties of the system must be defined.
Finally, if LES turbulence model is being used, LES delta coefficient should be set as well.
Initial and boundary conditions
In a convective heat transfer simulation, the computational domain will be solved for three fields: pressure (p), velocity (U), and Temperature (T). Depending on the choice of solver, additional turbulent transport quantities may be included. As a general rule for CFD simulations, all field conditions must be well-defined on all boundaries. Therefore, it is very important to define appropriate initial and boundary conditions for all variables on every boundary.
Important
Initial and boundary conditions must be specified for all variables on every boundary.
It is recommended to set the initial conditions close to the expected solution to avoid potential convergence problems. For this analysis type, variables could be initialized using the following methods:
Finally, the following boundary conditions are available for each variable:
Important Information
In case no boundary condition is assigned to some face/faces, by default these faces will be assigned a No-Slip wall BC, and zero gradient for temperature.
In case Radiation feature is enabled, in addition to above BC, the face/faces will be assigned a grey body radiative behavior with emissivity of 0.9.
Advanced concepts
Based on the choice of solver, the following Advanced concepts are available in a convective heat transfer analysis:
Numerics
Numerical settings play an important role in simulation configuration. Ideally, they could enhance stability and robustness of the simulation. Since the optimal combination is not always trivial to find, default values are tried to be as meaningful and relevant as possible. However, all numerical setting are made available for users to have full control over the simulation. These settings are divided into three categories:
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- Properties
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All properties regarding the iterative solvers of velocity and pressure equations are set here. Relaxation factors, residual controls, and solver-specific tweaks are among these settings. However, depending on the solver (e.g. PIMPLE, PISO, …), these settings will be adjusted. For each field, a Help message is provided on the platform.
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- Solver
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In this part, linear solvers used in computing each variable could be chosen separately. Upon choosing a solver, a set of preconditioners/smoothers and their tolerances become available. To assist with selecting the best solver, a Help message is provided for each field.
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- Numerical Schemes
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These schemes determine how each term in the governing equations should be discretized. Schemes categorized in the following groups:
- Time differentiation
- Gradient
- Divergence
- Laplacian
- Interpolation
- Surface-normal gradient
Simulation Control
The Simulation Control settings define the general controls over the simulation. Number of iterations, simulation interval, timestep size, and several other setting could be set. The following controls are available:
Result Control
Result Control allows users to define extra simulation result outputs. Each result control item provides data that requires additional calculation. The following result control items are available:
Disclaimer
Convective heat transfer analysis is performed using the OPENFOAM® software. See our Third-party software section for further information.
This offering is not approved or endorsed by OpenCFD Limited, producer and distributor of the OpenFOAM software and owner of the OPENFOAM® and OpenCFD® trade marks. OPENFOAM® is a registered trade mark of OpenCFD Limited, producer and distributor of the OpenFOAM software.