Effect of Pectoral Fin Rays of Flying Fish on the Aerodynamic Performance

Abstract

In the present study, we experimentally investigate the aerodynamic role of pectoral fin rays of flying fish and apply the concept of pectoral fin rays to a two-dimensional rectangular flat-plate airfoil. We consider two flying fish models, stuffed in an appropriate gliding posture, with and without pectoral fin rays. For this purpose, we directly measure the aerodynamic forces (i.e. drag and lift forces) on the flying-fish models in a wind tunnel. The Reynolds number based on the chord length (c) of pectoral fin is 19000 ~ 22000. The pectoral fin rays of flying fish enhance the lift coefficient by up to 25% at -15◦ < AOA < 0◦, where AOA is the angle of attack. The pectoral fin rays also increase the lift-to-drag ratio by up to 28% at -10◦ < AOA < -5◦, indicating that the pectoral fin rays enhance the aerodynamic performance of the flying fish. In the wake behind the pectoral fin, the velocity passing over the upper surface of pectoral fin increases, whereas that under the lower surface decreases,which overall increases the circulation and thus enhances the lift force. This effect is similar to what is observed from the Gurney flap. We also apply the concept of pectoral fin rays to a two-dimensional rectangular flat-plate airfoil by attaching the cylindrical-shape trip wire(s). The Reynolds number based onthe chord length (c) is 20000 and 80000. Various configurations of trip wires(s) are attached on the upper / lower surface of the airfoil. It is shown that the trip wire(s) attached on the lower surface increases the lift coefficient, showing a similar aerodynamic characteristics to that of flying fish with the rays. However, the lift coefficient decreases when the trip wire(s) are attached on the upper surface of the airfoil.