Volumetric Photon Monte Carlo (VPMC) Radiation Model Reference
The Volumetric Photon Monte Carlo (VPMC) method uses probability distributions to model photon transport in a way equivalent to solving the radiative transfer equation (RTE). Given its statistical nature, accuracy and computational cost both increase with the number of photon bundles used in the simulation.
In this method, the radiative processes (such as emission, absorption, scattering, boundary interaction, and so on) are modeled explicitly in a stochastic sense, as opposed to obtaining a numerical solution of the RTE or its simplified form. In this approach, the radiative processes are modeled by tracing the history of a large number of photon bundles (representative samples of radiative energy) in the computational domain. The generation of these photon bundles mimics the emission process of photons, and the interaction of these photon bundles with the medium and the surfaces as they travel in the computational domain represents absorption, scattering, and the radiation boundary treatment.
| Theory | See Volumetric Photon Monte Carlo (VPMC) Radiation. | ||
| Provided By | |||
| Example Node Path | |||
| Requires |
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| Activates | Physics Models | Solar Radiation | |
| Boundary Inputs | See Photon Monte Carlo Boundary Settings. | ||
| Region Inputs | See Photon Monte Carlo Region Settings. | ||
| Solvers | Photon Monte Carlo. See Photon Monte Carlo Solvers. | ||
| Field Functions | Boundary Irradiation, Boundary Irradiation on External Side, Boundary Radiation Heat Flux, Boundary Radiation Heat Flux on External Side, Boundary Radiosity, Boundary Radiosity on External Side, Incident Radiation, Radiation Patch Id, Radiation Patch Id on External Side, Radiative Absorption, Radiative Energy Source, Total Absorption Coefficient, Total Emissivity, Voxel Partition | ||
Photon Monte Carlo Boundary Settings
- Free Stream, Pressure Outlet, Wall, and Inflow Boundaries
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- Custom Patch Angularity Specification
- Patch angularity defines the maximum allowed angle between the normals to contiguous boundary faces for these faces to belong to the same patch. It provides a control over the patch planarity and is used to detect sharp angles in the geometry, such as would happen at a corner, and to prevent patches from bridging such features. The angularity is set at 150 degrees by default and would require changing only in cases where specific geometric features must be captured.
- Custom Patch Specification
- The
number of patches and patch angularity can be further refined or
customized at individual boundaries under the Physics
Conditions node. Specifies whether the number of
patches is set to Use Region
Values or custom values. When you
choose either Proportion of
Faces or Total, the
corresponding value node appears for the boundary, and you can
then enable Specify by Part
Subgroup.
注 If a region-level patching specification has Specify by Part Subgroup on, the Use Region Values option cannot be used for interface boundaries corresponding to boundary-mode interfaces in that region. Boundaries for contact-mode interfaces do support this option. See Interface Options. - Radiation Flux Option
- This
option allows you to model diffuse or directed radiation sources
at boundaries according to your own specification. See Diffuse Radiation Flux and Directional Radiation Flux.
Radiation Flux Option Corresponding Physics Value Nodes No flux None Diffuse radiation flux - Diffuse Radiation Flux
- The diffuse radiation flux is specified as a scalar profile. Requires the Multiband Thermal Radiation or Gray Thermal Radiation model. See Diffuse Radiation Flux.
Directional radiation flux - Directional Flux Orientation
- The direct radiation flux is specified by its direction (default [0.0, 0.0, 1.0]) and the divergence angle of the beam (default zero).
- Directional Flux Power Distribution
- The power of the directional flux is specified as a scalar profile. In addition to standard profile methods, a Gaussian method is also available. Requires the Gray or Multiband Thermal Radiation model.
Volume Photon Monte Carlo Region Settings
- Patch Angularity
- Patch angularity defines the maximum allowed angle between the normals to contiguous boundary faces for these faces to belong to the same patch. It provides a control over the patch planarity and is used to detect sharp angles in the geometry, such as would happen at a corner, and to prevent patches from bridging such features. The angularity is set at 150 degrees by default and would require changing only in cases where specific geometric features must be captured.
- Patch Specification
- Overall description of this condition node.
- Radiation Transfer Option
- Specifies that a region uses S2S radiation. Either a baffle or porous baffle must be placed between any two regions where only one region has this option activated. This baffle ensures that rays do not pass into regions where S2S is deactivated from regions where it is activated.
Volumetric Photon Monte Carlo Solver Properties
- Verbosity
- Provides
additional output during the Photon Monte Carlo calculations.
- None
- No output.
- Low
- Displays ray tracing progress.
- High
- Displays additional progress and resource usage information.
- 冻结求解器
- 开启时，求解器在迭代过程中不更新任何物理量。该选项默认情况下关闭。这是一个调试选项，由于缺少储存，它可能导致不可恢复的错误和错误的求解。有关详细信息，请参见有限体积求解器参考。
- Child Nodes
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- Ray Tracing Parameters
-
- Rays Per Patch
- The average number of rays (photon bundles) traced from each patch. The default is 10.
- Rays Per Cell
- The average number of rays (photon bundles) traced through each cell. The default is 10.
- Maximum Polygons Per Voxel
- Controls the resolution of the voxel mesh that is used in ray tracing. Lowering the value increases the resolution of the voxel mesh. This property generally does not need to be changed from the default value of 50. Increasing the number slightly decreases memory requirements, but can also slightly increase the calculation time.
- Max Ray Bounces
- The number of times a ray can bounce off a surface when being traced. The default is 1000.
- Max Volumetric Scatters
- The number of times a ray can be scattered in a volume when being traced. The default is 30.
- Environment Load Parameters
-
- Rays Per Patch
- The number of rays traced from each patch for computing environment loads. The default is 128.
- Statistical Sampling Factor
-
- Sampling Factor
- A
constant or user-defined field function specifying
what fraction of the latest PMC computation (at a
given iteration) contributes to the aggregated
solution. At a value of 1, the aggregated solution
is set to the latest PMC ray tracing solution,
whereas a value of 0 means that the aggregated
solution stays unchanged. For a value of 0.5, the
aggregated solution is updated by taking half of the
latest solution and half of the previous aggregated
solution. See Statistical Sampling
Factor.
Use high sampling factors at the start of the simulation or during any simulation transients, since that leads to faster feedback of radiative solutions into the energy equation and, consequently, faster evolution of the temperature fields. This is similar to the use of under-relaxation factors for flow and energy, where using low factors while the solution is evolving negatively impacts the solution convergence. A small value of sampling factor behaves likewise; it leads to radiative source terms that are not truly indicative of the temperature fields, which slows down the further evolution of the solution.
-
- Iteration Update Frequency
- Specifies how often the Photon Monte Carlo calculations are solved. The default is 1 (once every iteration for steady runs, once every time-step for unsteady runs). A value of 10 would mean once every ten iterations for steady simulations, every ten time-steps for unsteady simulations.