AEC Results Visualization in Simulation CFD
Anemometers, manometers, thermocouples, smoke testing, helium-filled balloons, and IR cameras can all be used to capture the movement of air and thermal gradients in a space. These methods extract data at specific locations and time which can be used to develop a limited depiction of performance in the space.
Simulation CFD extends the limitations of physical testing by proving an infinite number of anemometers for air flow measurement, manometers for pressure, thermocouples for temperatures, trace particles to follow streamlines (path of air), and an assortment of other data extraction and results visualization tools to fully interrogate performance. These tools are used to assess performance, identify opportunities to improve that performance, and quantify the impact design modifications can have on performance.
Before proceeding, review the following information to become acclimated with the definition and usage of the results visualization and data extraction tools in Simulation CFD:
Essential Skills Videos
- How to use Results Planes
- How to use Iso Surfaces
- How to Modify Part Appearance when viewing Results
- How to Assess Wall Results
Simulation CFD offers a variety of well-documented tools and methods to visualize results. Rather than reiterate existing documentation, this section will follow a single workflow for results visualization that is used to uncover a design deficiency and implement an informed design modification.
Flow and thermal performance of a small office space will be evaluated by looking at results globally and then interrogating operating characteristics locally. Globally reviewing results entails a comparison of expected velocity and temperature magnitudes to the simulation solution as well as a verification of the flow direction. Local interrogation is a matter of digging deeper into the simulation results to extract views and data necessary to improve design.
It is common to first review results globally at the “50,000 foot view” and then proceed with local interrogation of specific regions. Global results provide information relating to the minimum and maximum values in the analysis, as well as the confirmation of flow direction at openings and momentum sources.
The default results view is of velocity, making many surfaces dark blue as walls have zero (0) velocity magnitudes.
|Default velocity results view shown above. All walls display a zero (0) velocity (dark blue) while supply (1), return (2), and the computer (3) show a non-zero velocity.|
By default the results legend will use the global minimum and maximum values found in the analysis for the respective quantity displayed.
TIP: Comparing the legend maximum to the expected range which typically occurs at inlets, outlets, or momentum sources is a good first step in verifying the validity of simulation results. If the maximum value in the scale is much higher than expected, review the geometry, mesh, and inputs.
If heat transfer was solved for, changing the global results to temperature provides visualization of thermal gradients on model surfaces.
Again, the default scale for the global results quantity displayed should be compared with expected values. In this instance the human is within an acceptable range for simulation (90 F +/- 10 degrees) and the walls are within expectations (90F windows in front of desk, 75F for all other external walls, due to inputs).
The next logical progression in interrogating simulation results globally is to verify the flow direction across simulation openings (inlets and outlets) and momentum sources.
Global vectors help to visually confirm flow direction. Here flow is moving in and out of the respective supply and return. Oftentimes global vectors are used to find an erroneous flow boundary condition direction.
Another valuable global results tool is the Summary File, which is a text file used to summarize the output of an analysis.
After confirming simulation values globally, smaller localized regions are interrogated using several results visualization tools. Dissecting the model is accomplished with Planes. Planes are the most widely used results visualization tool that not only provide valuable insight on their own but also act as a starting point for other results visualization tools such as the bulk calculator, XYplots, and trace particles.
Newly added planes take on the global results quantity. In the images above, note the relationship between the temperature and velocity results. Modifying the results legend scale can help visualize the gradients involved and their relationships to each other.
Modifying the velocity scale and viewing the cut plane with vectors helps visualize flow gradients and direction. The final view from above uncovers air flow moving from the computer toward the supply. This flow field was not as prevalent with the default scale and shaded cut plane settings.
Further interrogation (additional planes at various locations and scales) reveals recirculation from the equipment (computer) outlet to inlet.
|A plane is re-oriented to further interrogate the equipment flow fields and reveals recirculation from outlet to inlet|
Vectors on the same plane provide additional understanding of the velocity gradients and direction in the room.
|High velocities near the return wall are shown to move toward the equipment|
Insight into flow-fields across several cut planes reveal recirculation in the room and equipment. To further interrogate the phenomena and understand the cause, additional results visualization tools are used to view the flow fields in a 3D manner as opposed to the 2D plane.
The overall picture of flow movement is becoming clearer with each visualization tool. Using trace particles provides further insight on the air flow path.
Interrogating the flow patterns in the space reveals opportunities to improve the air flow distribution by eliminating the recirculation of the equipment and along the back wall. The results can be used in design reviews with colleagues to brainstorm potential solutions that would be implemented in simulation, to verify their impact. Supply and return location, size, diffuser type along with equipment location, containment walls and various other design modifications are all potential solutions to improve performance.
An evaluation of a supply diffuser that directs flow downward, as opposed to the throw moving directly towards the return wall, is one simple solution that is implemented from interrogation of the existing system.
The Decision Center can be used to compare the impact of modifications by viewing results views and extracted data side by side.
The new diffuser (right) modifies the direction of supply air and carries the equipment exhaust toward the return wall.
The modified design (right) reduces the recirculation of hot air, lowering air temperatures in the space.
While optimizing the air flow distribution and location of a single computer in a small space may be impractical, this simple example conveys a process for results interrogation and interpretation that can be applied in an assortment of applications. Results are verified for validity and interrogated to uncover operating characteristics that may be difficult to capture in the real world.
For AEC applications with occupants, a set of results visualization tools associated with thermal comfort are available. The comfort of an occupant is a function of both their immediate environment and personal factors such as metabolic rate and clothing.
|Top row depicts the comfort temperature (left) and predicted mean vote (right) of the occupant in the two design scenarios previously shown.|
More information on Thermal Comfort results is available at the following resources.
- Thermal Comfort definition with technical references in the help.
- A description of the setup guidelines can be found in the help.
- Thermal Comfort Factors, can also be modified and are described in the help.
- Available Thermal Comforts are listed here.
- A step by step tutorial is also included with the software and can be found here.
An Autodesk Webinar, Introduction to Results Visualization, has a more in-depth overview of some of the capabilities of results visualization and has an AEC application as one of the models (flow over a stadium).