Abstract: In recent years, relevant studies have shown that wing sections with humpback whale-like leading-edge protuberances can effectively delay stall and improve aerodynamic performance after stall. To investigate the flow separation phenomenon of the biomimetic leading-edge protuberances wing section, a particle image velocimetry (PIV) experimental study on the NACA 63₄-021 wing section and modified wing sections with single and double leading-edge protuberances is carried out. The distributions of statistics such as the average velocity of the wing section suction surface and the turbulent kinetic energy at different angles of attack are compared. The proper orthogonal decomposition (POD) method is adopted to analyze the experimental data. The flow structures during the stall process are analyzed from an energy perspective. The study finds that: both single and double leading-edge protuberances wing sections have two-step stall characteristics. When a unilateral stall occurs, there is a stable attached flow at the convex peak, which suppresses the extension of the stall zone to the other side of the convex peak and plays a role similar to a wing blade. Compared to the single leading-edge protuberance wing section, the wing section with double leading-edge protuberances undergoes stall mode transition at smaller angles of attack. The energy of each mode of POD decomposition is related to the stall mode at which the wing section is located. The characteristics of the flow structure in the flow field change with the switching of stall modes. The flow separation mode of the single leading-edge protuberance wing section exhibits instability during the transition from unilateral stall to bilateral stall. This study provides an experimental reference for the theoretical research and potential engineering application of biomimetic leading-edge protuberances wing sections.