This paper details an aeroelastic concept for an adaptive and passive wing, which is primarily aimed for use within 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 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 prestall 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 non-dimensional reduced frequencies in a range of 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°-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.

The fluid–structure interaction of a pivoting rigid wing connected to a spring and subjected to freestream airflow in a wind tunnel is presented. Fluid–structure interactions can, on the one hand, lead to undesirable aerodynamic behaviour or, in extreme cases, to structural failure. On the other hand, improved aerodynamic performance can be achieved if a controlled application within certain limitations is provided. One application is the reduction of drag of road vehicles at higher speeds on a straight, while maintaining downforce at lower speeds during cornering. Conversely, another application concerns increased downforce at higher windspeeds, enhancing vehicle stability. In our wind tunnel experiments, the angle of incidence of the spring-mounted wing is either increased or decreased depending on the pivot point location and spring torque. Starting from a specified initial angle, the aerodynamic forces overcome a pre-set spring preload at incrementally increased freestream velocity. Reynolds numbers at a range of Re = 3 × 104 up to Re = 1.37 × 105 are considered. The application of a symmetrical NACA 0012 and a cambered NACA 6412 airfoil are tested in the wind tunnel and compared. For both airfoils mounted ahead of the aerodynamic centre, stable results were achieved for angles above 15 and below 12 degrees for the symmetrical airfoil, and above 25 and between 10 and −2 degrees for the cambered airfoil. Unsteady motions were observed around the stall region for both airfoils with all spring torque settings and also below −2 degrees for the cambered airfoil. Stable results were also found outside of the stall region when both airfoils were mounted behind the aerodynamic centre, although the velocity ranges were much smaller and highly dependent on the pivot point location. An analysis is reported concerning how changing the spring torque settings at each pivot point location effects performance. The differences in performance between the symmetrical and cambered profiles are then presented. Finally, an evaluation of the systems’ effects was conducted with conclusions, future improvements, and potential applications.