Hydrofoil geometry and leading-edge modifications: Influence of section profile, aspect ratio, and sweep

Abstract

Modifications mimicking the leading-edge protuberances on the pectoral fin of humpback whales have been widely adopted to the designs of foils and control surfaces to delay stall and provide post-stall superior lifting characteristics. However, the efficacy of these modifications in flow control and lift augmentation depends on the wing geometry. The present work investigates the lift, drag, and flow characteristics of finite-span hydrofoils with different section profiles-both symmetric and cambered (NACA 0012, NACA 0018, NACA 634-021, NACA 2412, and NACA 4415) having twin-protuberances over their leading-edge at a Reynolds number of 2 × 105. The influence of aspect ratio (1, 2, and 3) and leading-edge sweep angle (0 deg, 15 deg, and 26.1 deg) on the hydrodynamic performance of modified foils is also investigated. The characteristic feature of twin-protuberance foil designs is the restriction of flow separation between the chordwise vortices shed from the two protuberances in certain post-stall regimes. The use of leading-edge modifications is observed to be more conducive for lift enhancement in thin foil sections, especially NACA 0012, having a smaller stall angle. Considering the other parameters, leading-edge protuberances are observed to be advantageous for hydrofoils with aspect ratios 2 and 3 at post-stall angles of attack, and for 0 deg and 15 deg sweep angles for post-stall lift enhancement. The influence of Reynolds number on the performance modifications is also investigated.