Abstract
Experimental data for untwisted airfoils are utilized to propose a model for predicting the lift coefficients of twisted airfoils with leading-edge tubercles. The effectiveness of the empirical model is verified through comparison with results of a corresponding computational fluid-dynamic (CFD) study. The CFD study is carried out for both twisted and untwisted airfoils with tubercles, the latter shown to compare well with available experimental data. Lift coefficients of twisted airfoils predicted from the proposed empirically-based model match well with the corresponding coefficients determined using the verified CFD study. Flow details obtained from the latter provide better insight into the underlying mechanism and behavior at stall of twisted airfoils with leading edge tubercles.
Highlights
The ventral fins of the humpback whale include a tubercled leading-edge which is conjectured to serve as a natural lift-enhancing device
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
Many researchers have suggested that leading-edge tubercles have prominent effects on improving stall behavior since the control mechanism of leadingedge tubercles is similar to vortex generators that generate streamwise vortices.[3,6,7]
Summary
The ventral fins of the humpback whale include a tubercled leading-edge which is conjectured to serve as a natural lift-enhancing device. Flow field and aerodynamic forces of a two-dimensional (2D) airfoil with sinusoidal leading-edge tubercles were computed by Dropkin et al.[11] using the Spalart-Allmaras model at Reynolds number 180,000 They found that the low-pressure pockets persist at high angles of attack, resulting in the retention of lift. 104 106 which is considered to be a low Reynolds number flow according to Lissaman.[19] The flow in this region displays a transitional behavior.[20] Many researchers have suggested that leading-edge tubercles have prominent effects on improving stall behavior since the control mechanism of leadingedge tubercles is similar to vortex generators that generate streamwise vortices.[3,6,7] The advantages of leading-edge tubercles can be summarized as milder stall behavior, better post-stall performance, and a more stable dynamic stall characteristic. The effectiveness of the empirical model is verified through numerical analysis, in which, flow details are investigated to obtain further understanding of the control mechanism and stall behavior of twisted airfoils
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