On the response of the thin airfoil under multiscale gusty flows

Greenberg and Isaacs' theories are typically used for sinusoidal incoming flows, and their practicality in predicting lift overshot for thin airfoils with small angles of attack has been well established. In this study, we conducted experiments using a moving net to generate a multiple scale sinusoidal free stream. The main objective was to assess Isaacs' theories under random multiple scale waves with varying combined reduced frequencies, while maintaining constant small angles of attack on a NACA 0012 airfoil. The results showed the validity of Isaacs' theory when applied to multiple scale sinusoidal free stream conditions. First, the underlying reason was theoretically analyzed; second, to further validate the classic theory, we employed a time-resolved particle image velocimetry method to analyze the evolution of the flow field. Additionally, the momentum conservation approach was utilized on the control surface to quantify the lift coefficient contributions. Comparisons of the velocity magnitude evolution served as the foundation for understanding the airfoil-gust interaction response.