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Slow down to go faster?

One of the perennial requests that we receive is to make FLOW-3D faster. While we’re always making performance improvements with new models and methods (see, for example, some of the new features in FLOW-3D v10.1 and the development note about FLOW-3D/MP v5.0 in this issue), there are many things that a user can do in the simulation setup to help improve analysis turnaround time. Some high-level simulation setup suggestions intended to reduce the overall analysis time will be the focus of this article.

To begin, it is useful to look at the entire analysis process, from simulation setup to analyzing the results, to note where time is spent. A typical workflow is illustrated in Figure 1. Note that the time required to run the simulation is just a portion of the overall analysis time.

There are two steps in this process that could use some additional clarification: (1) determining how to model the problem and (2) creating the input file for the simulation. The first step involves figuring out what models, options, mesh sizes, etc. are necessary to model the process, while the next step is simply transcribing these options into the input file.

A typical CFD workflow allows users to reduce analysis time
Figure 1. This diagram shows a typical workflow for an analysis and illustrates why it is so important to avoid mistakes in the early stages of an analysis.

The first notable observation about this workflow is that just a few mistakes can significantly increase the analysis time, especially if they are not caught until postprocessing the results. This is not surprising, but the importance of being careful and catching mistakes early should not be underestimated. A second observation is that the duration of a given step in the process depends on what happened in the preceding step. While obvious, this point is valuable because it implies that the first step, determining how to model the problem, is the most important stage of the process since it affects all the following steps in the analysis. From these two simple observations we can derive some useful conclusions about where to focus effort during the analysis:

Adapting the three conclusions above into a short checklist provides the following guidelines to help reduce analysis times.

Download a printable version of this checklist >

Simulation setup checklist:

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