Defining Solar Radiation in Fluid Physics

You can specify the intensity and the direction of the solar radiation in the fluid physics of your simulation.

This task shows you how to:

See Also
About Solar Radiation in a Thermal Flow Simulation

Specify Solar Radiation Values Directly

  1. From the Solar values options, select Specified.
  2. Specify the Direct irradiance, which is the solar radiation that comes directly from the sun and makes it through the atmosphere unscattered to the model in a straight line.
  3. Specify the Indirect irradiance, also known as the "diffuse" irradiance, which is the solar radiation that is scattered by the atmosphere and hits the geometry from different angles.
  4. Specify the Axis system definition that describes the sun's location for the simulation by selecting one of the following:
    OptionDescription
    Global Specify the sun's location using an axis in the global coordinate system.
    LocalSpecify the sun's location using an axis in a local coordinate system, then select the axis system from the 3D area.
  5. From the Sun direction options, specify X Axis, Y Axis, or Z Axis as the direction of solar radiation in the selected axis system.
  6. Optional: From the Ground effect options, select Specified to simulate that some solar radiation is reflected back from the ground. When you enable ground effects, you can also adjust any of the following options as well.
    OptionDescription
    Ground reflectivity Measurement of how much solar radiation the ground reflects. Fully reflective is 1, fully absorbant is 0.
    Ground heightDistance from the ground to the origin (0, 0, 0) along the "up" axis for the simulation.
    Ground planeLocation of the ground plane, which can be in the X-Y plane, X-Z plane, or Y-Z plane.
  7. Specify the Spectral fraction, which determines the fraction of the overall energy coming from the sun that is in the visible band. A value of 1 means all of the energy is in the visible band, and a value of 0 means all of the energy is in the IR band.
  8. Optional: Expand the Clustering parameters to adjust values that determine the computational cells for solar radiation. You might want to adjust these parameters to reduce the computational cost of the simulation by merging cells.
    1. Describe the method for describing the cluster size from the Cluster size specification options as follows:

      Option Description
      Faces per cluster Specify cluster size in terms of faces in each cluster, then specify the number of faces in the Faces per cluster field that appears.
      Cluster length limit Specify cluster size by specifying a maximum cluster length, then specify the length in the Cluster length limit field that appears.

    2. Adjust the Number of rays per cluster. For example, if your overall surface has 100 cells, a cluster size of 4 should yield 25 clusters.
    3. Adjust the Cluster angle limit, a value that enables you to keep the clusters from deviating too far from a planar orientation, which in turn can help you avoid having solar radiation in areas where it should not be. You can also specify a negative value for the cluster angle limit to define the limit on the other side of the orientation plane.

      For example, consider a box where one side is in direct sunlight but an adjacent side should receive no sunlight. If the clusters are allowed to form around the 90º angle of the box edge, the adjacent side of the box will receive some solar radiation. Reducing the cluster angle enables you to restrict solar radiation to your preferred locations.

Compute Solar Radiation Values Based on Location, Time, and Direction

  1. From the Solar values options, select Computed.
  2. Specify the Latitude and Longitude of the location being simulated, in degrees.
  3. Specify the Time zone where the simulation occurs and the Date and time where it occurs.
  4. Specify the Axis system definition that describes the sun's location for the simulation from the following choices:
    OptionDescription
    Global Specify the sun's location using an axis in the global coordinate system.
    LocalSpecify the sun's location using an axis in a local coordinate system, then select the axis system from the 3D area.
  5. Specify the East direction as the X-, Y-, or Z-axis.
  6. Specify the North direction as the X-, Y-, or Z-axis.
  7. Specify the Solar database type:
    OptionDescription
    Nrel Uses the formulas developed at the National Renewable Energy Laboratory. This type is the theoretical maximum for incoming solar energy; if you want to include cloud cover, you must also specify the Indirect fraction in the field that appears.
    Ashrae Uses the formulas presented in the ASHRAE handbook. This type includes the indirect portion.
  8. Optional: Expand the Computed solar parameters to perform a manual adjustment of the computed Direct irradiance, Indirect irradiance, and the Sun direction in the X-, Y-, and Z-directions.
  9. Enable ground effects to simulate that some solar radiation is reflected back from the ground.
    1. From the Ground effect options, select Specified.
    2. Adjust the Ground reflectivity, which is a measure of how much solar radiation the ground reflects. Fully reflective is 1, fully absorbent is 0.
    3. Adjust the Ground height, which is the distance from the ground to the origin (0, 0, 0) along the "up" axis for the simulation.
    4. Adjust the Ground plane, which is the location of the ground plane in the X-, Y-, or Z-direction.
  10. Specify the Spectral fraction, which determines the fraction of the overall energy coming from the sun that is in the visible band. A value of 1 means all of the energy is in the visible band, and a value of 0 means all of the energy is in the IR band.
  11. Optional: Expand the Clustering parameters to adjust values that determine the computational cells for solar radiation. You might want to adjust these parameters to reduce the computational cost of the simulation by merging cells.
    1. Describe the method for describing cluster size from the Cluster size specification options as follows:

      Option Description
      Faces per cluster Specify cluster size in terms of faces in each cluster, then specify the number of faces in the Faces per cluster field that appears.
      Cluster length limit Specify cluster size by specifying a maximum cluster length, then specify the length in the Cluster length limit field that appears.

    2. Adjust the Number of rays per cluster. For example, if your overall surface has 100 cells, a cluster size of 4 should yield 25 clusters.
    3. Adjust the Cluster angle limit, a value that enables you to keep the clusters from deviating too far from a planar orientation, which in turn can help you avoid having solar radiation in areas where it should not be.

      For example, consider a box where one side is in direct sunlight but an adjacent side should receive no sunlight. If the clusters are allowed to form around the 90º angle of the box edge, the adjacent side of the box will receive some solar radiation. Reducing the cluster angle enables you to restrict solar radiation to your preferred locations.