# Impact of HPC and Automated CFD Simulation Processes on Virtual Product Development--A Case Study
## 2 Materials and Methods
### Implementation
Within the case study, the formula student team had licenses to utilize 300 CPU cores in total, consequently resulting in a threshold of 45 million cells which could be processed in the HPC system simultaneously. Since there are no restrictions on hardware resources and other limiting factors, such as memory size, did not have an influence, the licenses can be seen as the major bottleneck in scalability for both the development workflow and the speedup of the solver itself. ## 3 Results

After describing the implementation of the automated CFD process on HPC systems in the previous section, this section will present the implications for product development. The scope of our research subject included a \"real-world\" application in which the aerodynamic package of a formula student open-wheel racing car was redesigned from scratch. A formula student team as an object of research is particularly interesting because there are short development cycles and often fewer restrictions compared to most industrial projects, which opens new possibilities for innovations based on high-fidelity CFD simulations. By using HPC, the formula student team was able to implement an automated optimization approach for the aerodynamics of their racing car. It was not possible for the Elefant Racing team to implement such an approach before due to the lack of computational resources. Before applying the workflow to the open-wheel racing car, a symmetric full-scale CFD simulation had to be set up in order to verify the initial mesh quality. The basis of the CFD model was CAD geometry in which all aerodynamically unnecessary elements (e.g., bolts, nuts) were removed. The surrounding fluid domain was meshed with polyhedrons including two refinement boxes to capture the recirculation zone. The fluid domain had a relatively large size compared to the racecar in order to minimize any unphysical impact of uniform boundary conditions. The resulting CFD model consisted of approx. 80 million mesh cells and was set up with a double precision, pressure-based 3D solver. Both laminar and turbulent cases were investigated. Exemplary insights into the model and results are shown in Figure 4a,b. The effect of HPC on the efficiency of Elefant Racing's product development can be illustrated by comparing the number of major design iterations to the previous years and by showing the progress within the season where the implementation is used for the first time (season 19/20). Thereby, major design iterations are defined as adding new parts or changing parts for fully redesigned versions. In contrast, changing positions or sizes of parts was conducted within an iteration. Therefore, there were up to 100 simulations within one single design iteration. The number of designs iteration before and after the availability of HPC is shown in Figure 5a. Furthermore, HPC leads to major design improvements, as the KPIs drag and downforce indicate in Figure 5b. \begin{table}
\begin{tabular}{c c} \hline \hline
**Cells/CPU** & **Avg. Wall Time per Iteration in s** \\ \hline \(\sim\)100,000 & 1.737 \\ \(\sim\)150,000 & 1.706 \\ \(\sim\)200,000 & 2.334 \\ \(\sim\)250,000 & 3.106 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Influence of the cell/CPU ratio on the avg. wall time per iteration. The use of an HPC-based and automated CFD setup increased the number of design iterations by 600%. Figure 5b reveals more details of season 19/20 when the new approach was used for the first time: Within this season, a significant increase in downforce by about 115% was achieved while the drag force was reduced by about 20% during the optimization

Figure 4: Excerpt from the results of the CFD workflow. (**a**) Exemplarily meshed fluid domain of the investigated case. (**b**) Pressure distribution over the structure in Pa.

Figure 5: Increment in simulations and progress within one year. (**a**) Number of conducted design iterations per season. (**b**) Progress achieved during the season 19/20 by the means of reduction in drag and the increase in downforce.