Abstract
Leading-edge protuberances on airfoils or hydrofoils have been considered as a viable passive method for flow separation control recently. In this article, the hydrodynamic performance of a NACA 634-021 (baseline) foil and two modified foils with leading-edge protuberances was numerically investigated using the Spalart–Allmaras turbulence model. It was found that modified foils performed worse than the baseline foil at pre-stall angles, while the lift coefficients at high angles of attack of the modified foils were increased. Both the deterioration of pre-stall and the improvement of post-stall performance were enhanced with larger amplitude of protuberance. Near-wall flow visualizations showed that the leading-edge protuberances worked in pairs at high angles of attack, producing different forms of streamwise vortices. An attached flow along some valley sections was observed, leading to a higher local lift coefficient at post-stall angles. The leading-edge protuberances were considered as sharing a similar mechanism as delta wings, increasing nonlinear lift at large angles of attack. The specific stall characteristics of this leading-edge modification could provide some guidelines for the design of some special hydrofoils or airfoils.
Highlights
In recent years, leading-edge protuberance modifications on airfoils or wings have attracted extensive attentions as a new passive control technique.[1,2,3] The idea was originally motivated by the physiological structures of humpback whales,[1] which are extremely agile and maneuverable especially when hunting prey despite their large sizes and rigid bodies
The results indicated that the stability of force coefficients was enhanced with leading-edge protuberance at Re = 2.0 3 105
The lift coefficient of the modified hydrofoil is lower at pre-stall region, the stall performance is improved in different ways
Summary
In recent years, leading-edge protuberance modifications on airfoils or wings have attracted extensive attentions as a new passive control technique.[1,2,3] The idea was originally motivated by the physiological structures of humpback whales,[1] which are extremely agile and maneuverable especially when hunting prey despite their large sizes and rigid bodies. The Spalart–Allmaras model, which has shown pleasant results in relevant numerical researches,[14,15,19] was applied to investigate the influence of leading-edge protuberance on the hydrodynamic performance of full-span hydrofoils at a low Reynolds number Re = 1.83 3 105. Longer spanwise domain length than the previous research by the authors[16] was set, attempting to verify the bi-periodic flow pattern shown by Custodio.[8] On this basis, the flow details as well as their influences on the local and total foil performance were explored, and the mechanism of the leading-edge protuberances on flow control was discussed.
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