Computational Modeling of Aerodynamic Design Trends for a Production SUV Subjected to Incremental Design Changes: Roof Spoiler and Underbody Geometry

<div>In this work, we evaluated computational fluid dynamics (CFD) methods for predicting the design trends in flow around a mass-production luxury sport utility vehicle (SUV) subjected to incremental design changes via spoiler and underbody combinations. We compared Reynolds-averaged Navier–Stokes (RANS) using several turbulence models and a delayed detached eddy simulation (DDES) to experimental measurements from a 40% scale wind tunnel test model at matched full-scale Reynolds number. Regardless of turbulence model, RANS was unable to consistently reproduce the design trends in drag from wind tunnel data. This inability of RANS to reproduce the drag trends stemmed from inaccurate base pressure predictions for each vehicle configuration brought on by highly separated flow within the vehicle wake. When taking A-B design trends, many of these errors compounded together to form design trends that did not reflect those measured in experiments. On the other hand, DDES proved to be more consistent and accurate across all vehicle configurations, producing more viable design trends in drag, base pressure, and wake velocity profiles than steady RANS aligning closer with the design trends obtained from the wind tunnel. Therefore, more confidence in the digital design from DDES can be attained. Meanwhile, RANS produces non-physical design trends for highly separated flows, making it questionable as an effective tool for automotive vehicle design.</div>