The Simulation CFD Workflow

The typical CFD workflow follows a consistent and repeatable sequence of equally important steps to complete a simulation.

The Simulation CFD workflow follows a consistent and repeatable sequence:   

Pre-processing

  • CAD
  • Materials
  • Boundary Conditions
  • Mesh Definition

Processing

  • Solving

Post-processing

  • Results Visualization
  • Validation
  • Each of these steps, introduced below, will be examined in greater detail later.

Pre-Processing

CAD

Every CFD simulation starts in the CAD platform of your choice.  Autodesk Simulation CFD, by design, does not have any embedded CAD tools but communicates with most popular CAD packages, including Autodesk Revit and Autodesk Inventor.  Production-level CAD models will typically require varying levels of modification to make them optimal for CFD simulation; this process is known as idealization. 


In preparing this CAD model for simulation, note how minor details such as door handles, door hinges, window moldings and wall outlets have been omitted from the model.

Materials

Fluids and solids are the primary material types with air being the most commonly used fluid in AEC applications.  A comprehensive library is included with Simulation CFD to cover the majority of material needs.  There are also special materials available, known as devices, which have been developed to more easily represent complex components such as fans or filters.  


This floor fan can be represented in a simulation more practically with a fan device, as depicted by the light blue cylinder to the right.

Boundary Conditions

The environment that the AEC application is subjected to is controlled with the use of boundary conditions.  For example, the conditioned air entering a space through a supply duct would require the definition of both the flow rate (e.g., cubic feet per minute) and temperature of the incoming air.  Sufficient boundary conditions must be defined to adequately represent the known flow and thermal inputs for each application.


The vertical orange stripe on the single face above indicates that it is a pressure opening where flow can enter or exit the domain.  The lack of any boundary conditions on the other faces shown indicate that they are all adiabatic walls where no flow or thermal energy can pass through.

Mesh Definition

Meshing is the process of breaking up the fluid and solid domains into many smaller regions; a requirement for the finite element method.  Since both solution accuracy and solver time are directly impacted by the mesh, it is important to define the appropriate settings here. 


The mesh is comprised of small regions known as elements; the individual element faces are depicted as small triangles.

Processing

Solving

Of all the steps in the CFD process, this is the only one that is primarily “hands-off” and does not require constant user interaction once the solver settings have been defined and the solver process executed.  The solution time will ultimately vary based on factors such as hardware capabilities and model complexity.


The solver takes the user-defined inputs at the top of the image and processes the mathematical equations to generate the results output depicted at the bottom.

Post-Processing

Results Visualization

The ultimate objective of every simulation is to understand design performance.  The skills needed to visualize and interpret results are just as important as those required to set up the simulation.  Simulation CFD offers a comprehensive suite of display options to accommodate a wide array of scenarios and user preferences. 


These particle traces are just one way to visualize the air currents in an AEC space.

Validation

One of the primary benefits of CFD is the ability to simulate complex scenarios where classic engineering methods fall short of providing a complete picture and physical testing is impractical.  However, as a final step, hand calculations and historical design knowledge should always be used to validate results.