Abstract
The present work analyzed efficiency performance of lift-based fin by using numerical method of Computational Fluid Dynamics (CFD). The simulation models were generated three-dimensionally comprises of lift-based and oscillating drag-based fins. Horizontal profile of the lift-based fins was an airfoil of NACA0012 to form wing-like fins, while vertical profile of the fins were divided into rectangular, tapered, and lunate shapes. Both lift and oscillating drag based fins have a similar aspect ratio, AR=4. Movement of the fins were categorized into two kinematic schemes of oscillating and radial-sculling. The present mechanism of radial-sculling, mostly in lift-based fin, divided the tail into an oscillating part and a wing-like fin, connected by a free-rotation joint. The fins were simulated in a constant low-frequency tail-beat of f=1 s-1 in a range of low-speed flow from 0.1-1 overall length (L)/s. A robust optimization method of Generalized Reduced Gradient (GRG) was performed to obtain an optimum value of simulation results. It is shown that fin angle affects efficiency performance of the lift-based fin. For the present simulation models of lift-based fins, the overall optimum efficiency occurs at fin angle between 40o-60o. In the variation of vertical profile shapes, the lift-based fin with lunate shape has a higher optimum efficiency than rectangular and taper shapes. However, in lower flow velocity or higher Strouhal number, a highest efficiency was achieved by the rectangular shape. By comparing the kinematic mechanisms, the present work shows that radial-sculling of lift-based fin has a superior efficiency than the oscillating mechanism of drag-based fin within the similar aspect ratio and oscillating properties. The efficiency performance can be related to the wake pattern behind the fin. The present study suggests the implementation of lift-based fin with radial-sculling kinematic scheme for the practical application in low-speed flow and low-frequency tail-beat environment.