RapidFlow is a fast fluid solver designed for thermal simulation and is fully integrated into the TAITherm solver. It is optimized to reduce computational time while maintaining similar accuracy in fluid modeling. Benchmarking studies show that RapidFlow can decrease computation time by up to tenfold when compared to transient TAITherm-CFD coupling. The solver achieved a faster and smarter balance between computational time and accuracy.   

How to Use RapidFlow with a TAITherm Model 

There are three basic steps to use RapidFlow with a TAITherm model: 

1. Create a Fluid Part:  Create a new Fluid part and select “Enable RapidFlow”. Ensure that the fluid has a defined position that is located somewhere within the desired fluid domain. 
   
   
2. Connect Surfaces: Connect any necessary surfaces to the fluid part using the part convection settings. This allows the solver to use RapidFlow data for modeling convection on those surfaces.  
3. Define Solver Settings: Outside of the TAITherm user interface, define desired RapidFlow solver settings and fluid conditions in a configuration text file. An example of this file can be found in your software installation directory. If you are on Windows, the path may look something like this:  
   "C:\Program Files\TAITherm\2025.1.0\rapidflow\examples\simple-cabin\cabin-fluid.config" 
   
   

Once setup is complete, the simulation can be run via the standard methods, such as using the run button in the GUI, from the command line, as part of a batch script, or via an automation software like CoTherm. After the simulation finishes, the thermal surface results can be viewed in TAITherm, and detailed fluid results can be viewed in ParaView. ParaView is an open-source visualization application that can be used to analyze the fluid field generated by RapidFlow. 

Reduced Computational Time 

Using RapidFlow in your simulation workflows can significantly decrease computational time while maintaining comparable fluid modeling accuracy. In a benchmarking study using complex models to compare transient TAITherm-CFD coupling to TAITherm-RapidFlow, RapidFlow has demonstrated the ability to reduce computational time by up to tenfold. The table below highlights a comparison of computational time required for a 30-minute transient cooldown and the average error compared against physical test data.  

Coupling with 1D Tools  

RapidFlow’s full integration into TAITherm means it has the same powerful co-simulation capabilities as the standard solver. A thermal model that utilizes RapidFlow can be coupled with 1-D system modeling tools, which allows for rapid automotive  HVAC simulations, complex controller design, controller optimization simulations, and much more. For example,  a simple model can couple TAITherm and RapidFlow and Gamma Technology’s GT-SUITE to analyze human thermal comfort, cabin thermal conditions, and HVAC energy usage in a car cabin. In this setup, the responsibilities are divided as follows:  

• GT-SUITE: Calculates HVAC system inputs based on a user-defined PID controller and passes HVAC inputs to RapidFlow at specified intervals. 

• RapidFlow: Models the fluid field and convection based on HVAC inputs from GT-SUITE and the thermal model geometry from TAITherm. It then maps the convection data from the interior cabin and human surfaces to the TAITherm thermal solver 

• TAITherm: Models conduction, radiation, and environmental factors like solar and wind. It also models human physiology and determines occupant overall sensation. Using the convection data from RapidFlow, it calculates temperatures and human physiological results. Occupant sensation data is then sent back to GT-SUITE to be used in the PID controller calculation. 

This example shows a PID controller implemented in GT-SUITE. The PID controller is set up to adjust the cabin air temperature (for a warmup scenario) based on a user-defined cabin occupant sensation target. In the image below, the red line is the “Actual” occupant sensation, the blue line is the “Target” neutral sensation (0), and the green line “Output” is the HVAC air temperature passed to RapidFlow.  

About the Author

Deniz Hinz, PH.D. is a Senior Thermal and CFD Engineer at ThermoAnalytics Inc., where he leads the development and validation of advanced cabin simulation methodologies. Deniz specializes in coupling 1D and 3D solvers with human thermal comfort modeling to create integrated multiphysics simulation workflows for cabin environments. Recognized for his meticulous approach and innovative problem solving, he delivers solutions that are both highly accurate and tailored to client-specific needs. Deniz holds a BSE in Chemical Engineering from the University of Michigan and a PhD from the Illinois Institute of Technology, where his research centered on CFD model development and validation for complex, multiphase flows.