SOLIDWORKS, Flow Simulation

Transient Thermal Analysis Made Easy With Flow Freezing

By Sam Skinner on July 6, 2020

SOLIDWORKS Flow Simulation makes solving complex fluid dynamics problems easy. Even though setting up a model may take only a matter of minutes, sometimes we run into scenarios that require a significant amount of computation time. For example, some problems deal with processes that develop at different rates and if the difference in the rate at which these processes develop is significant, the CPU time or solve time might be dominated by the slower process. In this article, we look at how to use the Flow Freezing capability in SOLIDWORKS Flow Simulation to complete these time-intensive computations.

Consider a pot of water being heated on a stove. When you turn the burner on, the water starts heating up from room temperature, and as it’s heating up, convection currents begin to form in the water. At some point, the convection currents reach a steady state meaning that the velocity field of the fluid is no longer changing. This ‘pseudo-steady-state’ condition typically occurs long before the water reaches the desired temperature. In this case, the velocity field and the thermal profile are developing at different rates and the thermal profile may, in some cases take minutes or even hours longer to reach a steady-state condition. If we want to simulate the complete physical time required to heat up the water the required CPU time could be substantial.

Water boiling diagram

Flow Freezing with SOLIDWORKS Flow Simulation

Flow Freezing in SOLIDWORKS Flow SimulationThankfully, Flow Simulation offers a unique capability, Flow Freezing, which helps us significantly reduce the time required to complete these time-intensive computations. Flow Freezing allows you to temporarily, periodically or permanently freeze or fix the velocity and pressure fields while continuing to compute the temperature or energy portion of the analysis. In this way, we can quickly simulate complex heating and cooling profiles. 

The heating and cooling profile of the CPU in your computer can be very complex. As your CPU heats up, heat may only be dissipated via natural convection, then the fan kicks on to circulate cool air through the system. After a few seconds, the air flow has reached a steady state profile, but your CPU may continue to heat up for some time. By periodically freezing the flow field, we can let the natural convection reach a steady state, then un-freeze when we start our fan and finally freeze again after the fans have reached steady-state.

We implement the Flow Freezing technique via our Calculation Control Options. By right-clicking on Input Data, we can select Calculation Control Options. From here, we access Flow Freezing by clicking on the Solving Tab where we can define our freezing strategy.   Calculation Control Options can also be accessed via the Flow Simulation solver window, so if you need to make changes to your strategy, or turn Flow Freezing on after you have started running your analysis, you have that flexibility.

Calculation Options in SOLIDWORKS Flow Simulation

Flow Freezing enables us to solve real-world problems that would otherwise be impractical! Watch the full video below to see Flow Freeze in action.


Do you want to learn more about SOLIDWORKS Flow Simulation? Check out or on-demand webinar where our Application Engineer shows you some of the features of Flow Simulation and how the software can improve your design process.

Launch Webinar