Numerical investigations of hydrodynamic performance of hydrofoils with leading-edge protuberances

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 63 4 -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 leadingedge 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.

Effect of a Single Leading-Edge Protuberance on NACA 634-021 Airfoil Performance

“…A pair of counter-rotating vortices stemming from the leading edge was considered to help keeping the flow attached to the suction surface, similar to the effect of a delta wing. The bi-periodic condition was verified through numerical simulation performed by Cai et al, and different modes of spanwise periodicity were discovered [12]. However, the formation mechanism of spanwise periodicity is still unclear, which needs further investigation.…”

“…Most of the leading-edge protuberances were designed as continuous uniform distribution [7][8][9][10][11][12], and the flow patterns resulted from joint effects. In order to investigate the formation mechanism of spanwise periodicity, it is very necessary to examine the effect of a single protuberance, and further discuss the interferences of vortex structures between different protuberances.…”

Numerical Investigation on Flow Separation Control of Low Reynolds Number Sinusoidal Aerofoils

“…Studies into its operation at low Reynolds numbers have spurred particular interests recently, due to their intriguing design characteristics and effects on flow separation behavior and vortex generation 2,3 . This research area draws its inspirations from the morphology of humpback whales which possess exceptional maneuvering and turning ability at higher velocities, especially when they are approaching their preys.…”

“…This research area draws its inspirations from the morphology of humpback whales which possess exceptional maneuvering and turning ability at higher velocities, especially when they are approaching their preys. It has been determined by earlier studies that the swiftness in the motion of a humpback whale is partially affected by the presence of pectoral flippers with leading-edge protuberances 3 . A detailed aerodynamic performance analysis of flippers with leading-edge protuberances was experimentally conducted by Miklosovic et al 4 at Re = 5 x 10 5 .…”

An empirically-based model for the lift coefficients of twisted airfoils with leading-edge tubercles

“…Nevertheless, it is noted that there was only one tubercle wavelength considered in Cai et al, 12 Gross and Fasel 13 noted that this may not be appropriate if a bi-periodic pattern occurred. Cai et al 15 made further numerical investigations of the hydrodynamic performance of hydrofoils with leading-edge tubercles at Reynolds number 180,000. The results suggested that a sufficiently large spanwise width of the airfoil is required to gain a better description of flow patterns around the leading-edge protuberance.…”