Numerical Simulation Of Winglet Characteristics For Drag Reduction

With the deterioration of the energy shortage and people's increasing concern about environmental issue, efficient, energy-saving, environmental friendly mode of economic development has become the major theme of the world economic development in the contemporary era. Airplane is a kind of efficient and fast means of transportation, it need to consume a large amount of fuel. Therefore, how to reduce fuel consumption and improve flight efficiency is increasingly concerned by the aircraft designers. The key of achieving this goal is to reduce the drag and increase the lift. Particularly, reducing the drag in flight is an important aspect to improve the characteristics of a large transport airplane. The drag of large-scale long-range transport airplane is mainly consist of induced drag, pressure drag and friction drag. It is noteworthy that the induced drag accounts for about 40% of the total drag during cruising flight, so reducing the induced drag is an important way for drag reduction, which is also the goal for the aircraft designers to make a concerted effort to solve.By the long-term observation of the large birds (such as eagles and falcons), it is discovered that they deflect their wings upward in flight to reduce the drag for gliding farther. The vortex was formed at the wing tip and resulted in the induced drag. Hindering the formation of wing tip vortex or destroying the structure of the vortex are the fundamental way to reduce the induced drag. So wing tip drag-reducing device such as cut tip, wing tip sails, wing tip winglet were invented. Currently, equipped winglets on large transport aircraft in the civilian has been concern widely by the airplane designers. It has become a necessary equipment of the new airplanes. Many countries put into a lot of manpower and financial resources to conduct relevant researches.Many shape parameters of winglet, such as the tilt angle, the installation angle, the airfoil of winglet, the height and the area of winglet, and so on, affect the drag reduction. Therefore, the drag reduction effects of different winglets are reported in many articles. In our country, the research is relatively weak because the design of large transport aircraft has just begun. In this thesis, a basic wing shape was created by selecting standard RAE2822 supercritical airfoil as the aerofoil of wing and referring to ARJ-21 wing size. On the basis of that, a new wing tip winglet was designed. The 3-D airflow over the wing is simulated by Fluent software, and the related theoretical analysis was done about the wing drag reduction effect.In order to provide a reference for comparing the drag reduction effect of the winglets, the 3-D numerical simulation of basic wing created by using standard RAE2822 supercritical airfoil as aerofoil of wing and referring to ARJ-21 wing size was simulated at first. Independent of mesh topology and the reliability of turbulence model were demonstrated numerically and it shows that numerical simulation is reliable. The numerical results are compared with the experimental data, and the results is proved to be reliable.Based on the simulation for the basic wing, the same simulation method and boundary condition are applied on 3-D numerical simulations for the wing with winglet. Comparing to the results of two wings, a conclusion about drag-reducing properties can be drawn. At the same Mach numbers and attack angles of attack, all the lift coefficients of the wings with winglet increased. When the Mach number is 0.65, the maximum of increment is 3.1%, the average increment is 2.0%. At Mach number of 0.7, the maximum of increment is 4.2%, the average increment is 2.8%. The drag coefficients of the wing with winglet decrease to the different degree. At Mach number of 0.65, the maximum of drag reduction rate is 14.4%, the average drag reduction rate is 11.8%. At Mach number of 0.7, the maximum of drag reduction rate is 11.2%, the average drag reduction rate is 10.2%. The maximum of increment is 18.7% in lift-drag ratio of wing, the increment is 16.8% at Mach number of 0.65, and the increment is 15.4% at Mach number of 0.7. Thus, aerodynamic performance of wing with winglet has been greatly enhanced.Comparing the two results of calculation, the aerodynamic characteristics and the drag-reducing mechanism of wing with winglet were analyzed in this thesis. Blocking air flow upward, dissipating energy of wing tip vortex, reducing downwash angle and downwash velocity within entire wing span, are the main reasons of winglet drag reduction.