Modeling of the compartmentalization effect induced by leading-edge tubercles

Abstract

As a passive flow control technique, the use of leading-edge tubercles inspired by humpback whale flippers has attracted much interest. It is believed that one of the flow control mechanisms of leading-edge tubercles is compartmentalization, which is similar to the way in which wing fences act. However, to date, there has been no direct evidence for this belief. In view of this, the present work aims to verify and quantitatively describe the compartmentalization effect induced by leading-edge tubercles. Numerical simulation is performed to investigate the flow structures on a wavy airfoil with leading-edge tubercles, and the results reveal the presence of typical biperiodic flow patterns when a critical angle of attack is exceeded. Based on the flow characteristics of the wavy airfoil, special fences paired in a diverging configuration are designed and positioned on the baseline airfoil. A modeling method is developed to determine the main parameters of the fence configurations. It is found that the fenced airfoils designed using this method are able to reproduce the typical flow characteristics of the wavy airfoil under different inflow conditions. The spanwise distributions of the sectional airfoil performance under flow control by leading-edge tubercles and by the specially designed fences are very similar. A combined mechanism mainly including the lifting-line theory and the compartmentalization theory is proposed to provide a more comprehensive picture of the flow dynamic of leading-edge tubercles. This work provides strong evidence to confirm the compartmentalization mechanism of action of leading-edge tubercles, as well as developing a quantitative modeling method, both of which are important for fully understanding the underlying mechanism and guiding further optimization of this passive flow control technique.