Investigation of Transient Aerodynamic Effects on Public Roads in Comparison to Individual Driving Situations on a Test Site

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.