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Aerodynamic development for road vehicles is usually carried out in a uniform steady-state flow environment, either in the wind tunnel or in Computational Fluid Dynamics (CFD) simulations. However, out on the road, the vehicle experiences unsteady flow with fluctuating angles of incidence &beta, caused by natural wind, roadside obstacles, or traffic. In order to simulate such flow fields, the Forschungsinstitut f&uuml, r Kraftfahrwesen und Fahrzeugmotoren Stuttgart (FKFS) swing&reg, system installed in the quarter scale model wind tunnel can create a variety of time-resolved signals with variable &beta, The static pressure gradient in the empty test section, as well as cD values of the Society of Automotive Engineers (SAE) body and the DrivAer model, have been measured under these transient conditions. The cD measurements have been corrected using the Two-Measurement Correction method in order to decouple the influence of the unsteady flow from that of the static pressure gradient. The investigation has determined that the static pressure gradient in the empty test section varies greatly with different excitation signals. Thus, it is imperative to apply a cD correction for unsteady wind tunnel measurements. The corrected cD values show that a higher signal amplitude, as in, signals with large &beta, lead to higher drag forces. The influence of the signal frequency on drag values varies depending on the vehicle geometry and needs to be investigated further in the future.

Natural wind, roadside obstacles, terrain roughness, and traffic influence the incident flow of a vehicle driven on public roads. These transient on-road conditions differ from the idealized statistical steady-state flow environment utilized in CFD simulations and wind tunnel experiments. To understand these transient on-road conditions better, measurements were performed on German public highways and on a test site. A compact car was equipped with a measurement system that is capable of determining the transient airflow around the vehicle and the vehicle’s actual driving state. This vehicle was driven several times on a predefined 200 km long route to investigate different traffic densities on public highways in southern Germany. During the tests the transient incident flow and pressure distribution on the vehicle surface were measured. With the same test vehicle, individual driving situations were recreated on a test site under weather conditions similar to those of the tests on public roads. This paper presents a comparison of the aerodynamic characteristics measured on public highways and on the test site. Two driving situations were examined at the test site: one is driving the test vehicle without traffic and the other is driving behind a box truck in different distances. This paper compares the realistic properties of the turbulent flow structures and the surface pressure around the vehicle during on-road driving in public traffic with those measured on the testing site. The purpose of this study is to investigate the possibility of reproducing the representative driving on public highways with a simplified approach.