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Despite the recent broadening of acceptable test methods for certifying aerodynamic performance, there has been little attention on how to determine the time averaging window used for providing mean forces. This is of particular relevance to the assessment of commercial vehicles as they are significantly affected by low-frequency patterns that are hard to predict and vary with different geometry configurations. Published guidelines in the industry suggest that good engineering judgement be used and a qualitative assessment of force histories is adequate. These suggested methods leave the accuracy of the time averaging to the experience and judgement of the user and is highly dependent on the specific characteristics of the benchmark case. Furthermore these methods are not able to quantify the error present due to motions slower than length of the sampled data.

While wind tunnels often serve as the standard tool for aerodynamic development of vehicles they do not routinely and feasibly offer detailed information into the fundamental fluid structures in and around the vehicle. It is up to the insight and experience of the aerodynamicist to determine what flow features are present and suggest improvements to the design. This is one of the reasons that the aerodynamic development of a vehicle can become a long iterative process. One tool for gaining more information about the flow is Computational Fluid Dynamics (CFD) simulations, but these methods are not infallible. By combining the fluid behavior information gained from CFD with the trusted measurements from wind tunnel experiments throughout the design process, it is possible to reduce the total time of a development project and produce a more robust and improved design. Discussed in this paper is an example case for a new production SUV.