Fluid-structure interaction of a spring-mounted symmetrical rigid wing for drag reduction of cars at higher wind velocities

This paper details an aeroelastic concept for an adaptive and passive wing, which is primarily aimed for use within the automotive sector to reduce drag and fuel emissions. The work will also be of interest in the motorsport sector to improve performance and also some applications within the aerospace and renewable energy sectors. The wind tunnel testing of a spring-mounted symmetrical NACA 0012 wing in freestream is studied over 0° to 40° angles of incidence. General operation of the concept is verified at low angles in the pre-stall region with that of a theoretical estimation using finite and infinite wings. Three distinct regions are identified, pre-stall, near-stall, and post-stall. The transient limitations associated in the near-stall region with variations in spring loading and flow velocities are discovered. It is identified as a periodic self-sustained oscillation with nondimensional reduced frequencies in the range from 0.14 to 0.22. Furthermore, performance in the post-stall region along with pre-stall is reported, and methods for the adjustment of the elastic element for a desired response are introduced. Evaluation is conducted with regard to an automotive application such as a rear wing on a high-downforce race car. Typically a 25% increase in wind velocity in the pre-stall region results in a 3° to 5° change in angle of incidence corresponding to a 25-40% reduction of drag coefficient depending on spring stiffness. Reductions of 20° in angle of incidence with similar 25% increase in wind velocity are typically found in the post-stall region. Even larger reductions are found when transitioning through the stall region. This work provides a valuable insight for a novel concept, but we only recommend its use in the pre-stall region to achieve steady results. Use at higher angles is only recommended if transient effects are not important. Limitations to this proof of concept work are highlighted and future development work is suggested to achieve further increases in performance.