Aerodynamic Influence of Deformations due to Wind Load on Full-Sized Passenger Cars 15-15-01-0001

In this article, a methodology is presented to assess the influence of time-averaged deformations on a production car of the 2018 A-class due to wind load. Exemplary, the deformations of the front and rear bumper are investigated. The aerodynamic development of vehicles at Mercedes-Benz is divided into several phases. When comparing force coefficients, differences can be observed between these distinct hardware stages as well as when comparing steady-state simulations to wind tunnel measurements. In early phases when prototype vehicles are not yet available, so-called aero foam models are used. These are well-defined full-sized vehicle models as the outer skin is milled from Polyurethane. Important aerodynamic characteristics such as an engine compartment with a cooling module, deflecting axles with rotatable wheels, and underbody covers are represented. As attachment parts such as the front and the rear bumper are also milled from Polyurethane, they cannot deform under wind load. Geometric deviations and deformations of the bumpers are a vital difference between the early prototype and a series production vehicle. Thereby, some of the drag differences between those two vehicle stages can be explained. Measurements of the deformations were conducted in the wind tunnel facility in Sindelfingen. The greatest deformations happen in the low-pressure regions at the sides of the front and rear bumpers and at the lower and the upper part of the front bumper. A quadratic behavior of the deformations over the velocity is indicated. When adding the deformations to a scanned geometry state, steady-state simulations indicate an increase in drag, but only little influence on the integral lift value. Transient Delayed Detached Eddy Simulation (DDES) confirms this trend.