Characterization of Aerodynamic Impact of Build Variation in Class 8 Tractor Trailers

Build variation and tolerance stack up are unavoidable in the vehicle manufacturing process, not only for individual components and assemblies but also for the vehicle at large. Deviations across several components, each within tolerance limits, could ultimately have a significant effect on vehicle aerodynamic performance. The objective of this study is to quantify the impact of several such build variations on vehicle drag. A Lattice-Boltzmann-based simulation method was used in conjunction with design of experiments to construct a Kriging response surface interpolation model to efficiently characterize the impact of 17 different body and chassis build variations on the aerodynamic drag of a VNL 780 tractor trailer at a nonzero yaw angle. The top three parameters with greatest aerodynamic impact were then evaluated at the opposite symmetric yaw angle to understand the impact of build variation on vehicle asymmetry. Finally, a Monte Carlo-based stochastic sampling was applied to the Kriging response surface interpolation models to quantify the distribution of drag variation for a known distribution of build variation parameters. The methodology provides a systematic approach for characterizing trends, ranking sensitivities, and quantifying aerodynamic performance impact from build variation.