Wake Structures and Surface Patterns of the DrivAer Notchback Car Model under Side Wind Conditions

• Main Authors: Dirk Wieser, Christian Navid Nayeri, Christian Oliver Paschereit
• Format: Article
• Language: English
• Published: MDPI AG 2020-01-01
• Series: Energies
• Subjects: drivaer; aerodynamics; wind tunnel; vehicle; flow visualization; piv; wake structures; side wind; crosswind
• Online Access: https://www.mdpi.com/1996-1073/13/2/320

The flow field topology of passenger cars considerably changes under side wind conditions. This changes the surface pressure, aerodynamic force, and drag and performance of a vehicle. In this study, the flow field of a generic passenger vehicle is investigated based on three different side wind angles. The study aimed to identify vortical structures causing changes in the rear pressure distribution. The notchback section of the DrivAer model is evaluated on a scale of 1:4. The wind tunnel tests are conducted in a closed section with a splitter plate at a Reynolds number of 3 million. The side wind angles are <inline-formula> <math display="inline"> <semantics> <msup> <mn>0</mn> <mo>∘</mo> </msup> </semantics> </math> </inline-formula>, <inline-formula> <math display="inline"> <semantics> <msup> <mn>5</mn> <mo>∘</mo> </msup> </semantics> </math> </inline-formula>, and <inline-formula> <math display="inline"> <semantics> <msup> <mn>10</mn> <mo>∘</mo> </msup> </semantics> </math> </inline-formula>. The three-dimensional and time-averaged flow field downstream direction of the model is captured by a stereoscopic particle image velocimetry system performed at several measurement planes. These flow field data are complemented by surface flow visualizations performed on the entire model. The combined approaches provide a comprehensive insight into the flow field at the frontal and side wind inflows. The flow without side wind is almost symmetrical. Longitudinal vortices are evident along the downstream direction of the A-pillar, the C-pillars, the middle part of the rear window, and the base surface. In addition, there is a ring vortex downstream of the vehicle base. The side wind completely changes the flow field. The asymmetric topology is dominated by the windward C-pillar vortex, the leeward A-pillar vortex, and other base vortices. Based on the location of the vortices and the pressure distributions measured in earlier studies, it can be concluded that the vortices identified in the wake are responsible for the local minima of pressure, increasing the vehicle drag.