Application of dynamic mode decomposition to influence the driving stability of road vehicles

The recent growth of available computational resources has enabled the automotive industry to utilize unsteady Computational Fluid Dynamics (CFD) for their product development on a regular basis. Over the past years, it has been confirmed that unsteady CFD can accurately simulate the transient flow field around complex geometries. Concerning the aerodynamic properties of road vehicles, the detailed analysis of the transient flow field can help to improve the driving stability. Until now, however, there haven't been many investigations that successfully identified a specific transient phenomenon from a simulated flow field corresponding to driving stability. This is because the unsteady flow field around a vehicle consists of various time and length scales and is therefore too complex to be analyzed with the same strategies as for steady state results. Dynamic Mode Decomposition (DMD) extracts the coherent structures from complex, transient flow fields, which can help to identify certain target phenomena. However, one issue in the practical application of DMD is the difficulty to find a connection between a computed mode and an actual aerodynamic effect on the body. To overcome this issue, we propose an extension of existing DMD algorithms that enables the interpretation of DMD modes such that they can be connected to the aerodynamic design. Here, we applied this extended DMD algorithm on the numerically simulated flow field around a simplified vehicle model. The DMD was able to identify the transient flow structures which potentially correspond to driving stability. Based on the DMD results, we developed a body kit that was expected to reduce the aerodynamic force fluctuations in the target frequency range. Finally, we verified that this body kit effectively controls the fluctuations. In summary, the proposed extended DMD algorithm can support the effective development of body kits for road vehicles to improve their transient aerodynamic characteristics.