Investigation of the decisive factor for the effectiveness of biomimetic protuberances during the stall process

Abstract

This study investigates the influence of leading-edge protuberances (LEP) on the stall process of airfoils to identify the decisive factor in the effectiveness of LEPs. Owing to its clearly defined three-dimensional structure, an LEP introduces uncertainties into its effects on the stall angle of attack and the lift coefficient curve. This poses a challenge for several airfoils when universal stall control strategies are adopted. These problems were studied by classifying 12 symmetrical baseline airfoil types based on their blade thicknesses under the condition of Re = 180 000. These include thin airfoil stalls (TS), leading-edge stalls (LS), and a combination of leading-edge and trailing-edge stalls (CS). Two representative airfoils from each category were selected to study single-protuberance airfoils. The distribution of the suction surface momentum and evolution of the spanwise vortices revealed that the streamwise vortices induced by the LEP resulted in an attached flow. However, the impact of these flow patterns varies depending on the type of airfoil used. The TS and LS airfoils experienced an increase in the stall angle and maximum lift coefficient, resulting in an overall improvement in the airfoil performance. The CS airfoils are the most heavily influenced, experiencing a decrease in the maximum lift coefficient and exhibiting phenomena such as a one-sided stall and step-by-step stall. Finally, this paper proposes for the first time that the main factor influencing the different effects of protuberances is the stall type of the airfoil. This new knowledge can serve as a valuable reference for the implementation of protuberances in practical mechanical applications.