| Organic evolution had been the experience of 4 billions years. There are many ingenious principle and structure, and the investigation of the organic evolution will be helpful for the technological innovation. Aquatic locomotion of fishes has been the research topics for a long time. Fish is capable of manipulating flow around the body both passively and actively. Passive control of flow rely on structural and morphological components of the body, such as humpback whale tubercles and riblets. Active control is the usage of appendage or body musculature to directly generate wake flow structures or stiffen fins against external hydrodynamic. Fish can actively control the curvature, displacement, and area of fin. It is an effective, simple and green way to seek for the methods of reducing the resistance of the viscous flow.The humpback whale flipper is unique because of the presence of the rounded protuberances or tubercles located on the leading edge, which give the surface a scalloped appearance .In spite of its huge size, humpbacks whales are very alert in their movement, and even can return 180 degree agilely. In this paper based on the drag reduction experiments of the humpback whale's pectoral structure, a similar leading edge of humpback whale pectoral fin with the"paraganglioma"has been made on the leading edge of NACA63-210 wing, an bionic NACA63-210 airfoil is designed with convex-concaved leading edges, and the 3-dimensional flows around the bionic wing are simulated for the drag reduction purpose.In order to improve the reliability of 3-D numerical simulation, the control equations and boundary conditions for standard NACA63-210 airfoil were given. By comparing the results with the original experimental data, we can conclude that the computational results agreed well with the experimental data, and show that our calculation are reliable.Based on the simulation for the standard NACA63-210 airfoil, the same simulation method, structural mesh and boundary condition are chosen for 3-D numerical simulations for the bionic NACA63-210 airfoil. We compared the lift and drag of two wings. At the same Reynolds number and angle of attack, the lift coefficient of the bionic airfoil is increased. The maximum of increment is 10.2%, and the minimum of increment is 3.7%. Numerical results show that the average increment is 6.9% at the Reynolds number of 9×104; the average increase rate is 7.8% at the Reynolds number of 1.2×105; and the average increment is 7.5% at the Reynolds number of 1.5×105 .At the attack angle greater than 0 degree, the ratio of lift to drag is increased, the maximum is 20.7%, and the minimum is as much as 10.3%. At the Reynolds number of 9×104, the average increment is 15.6%; at the Reynolds number of 1.2×105, the average increment is 14.6%; and the average increment is 15% at the Reynolds number of 1.5×105. At the attack angle greater than 0 degree, all drag are decreased, the maximum of drag reduction rate is 13.8%. At the Reynolds number of 9×104, the average drag reduction rate is 7.6%; at the Reynolds number of 1.2×105, the average drag reduction rate is 5.5%, and the average drag reduction rate is 7.9% at the Reynolds number of 1.2×105. It is illustrated that the aerodynamic characteristics of bionic wing is superior to that of standard wing.Numerical simulations show that at the Reynolds number of 9×104 and the attack angle of 6 degree, the total drag coefficient of the bionic wing decreased. The pressure difference drag coefficient decreased by 15% while the frictional resistance coefficient increased by 35.3%. Due to the fact that over 80% of the total resistance is composed of the pressure difference drag, the total resistance coefficient reduced. In this paper, the mechanism of total drag reduction of the bionic airfoil was explored with both pressure difference drag and frictional resistance. The reason of total drag coefficient reduction is its special configure design, its protruding leading edge which is actually a vortex-making machine. It generate the vortex of the opposite direction to the medial rotation vortex in the internal and posterior edge of the wing. The flow separation is delayed, which is also the major reason of pressure drag reduction.
|
PDF Full Text Request