Chapter 6
留學生工程dissertation代寫Simulation of the Drag Reduction Characteristics of Winglet

6.1 Introduction
With the further deterioration of the energy shortage and people's growing concern on environmental protection, high efficiency, energy saving, environmentally friendly mode of economic development has become a key theme of world development. Aircraft as an effective and efficient means of transport, its flight consumes a large amount of fuel needed to provide power, therefore reducing aircraft fuel consumption and increasing flight efficiency is the primary goal of aircraft design, attached great importance to countries in the world. The key to achieve this goal is how to achieve lift augmentation-drag reduction; especially large increase in aircraft performance will largely depend on the reduced air resistance. Thus, reducing the air resistance is a very important aspect of aircraft design. The main resistance of large-scale long-range transport aircraft consists of induced drag, pressure drag and friction drag, in its cruising state induced drag accounts for about 40% of the total resistance. To reduce the induced drag is an important way to achieve to drag reduction of aircraft, and the problem for aircraft designer to solve.
People through long-term observation of large birds (such as eagles and hawks) in nature, found that the wings of birds in flight feathers to the wing tips represented on the deflection to reduce the resistance, to enable them to glide distance. Inspiration from this phenomenon found that the air flow through the three-dimensional, the airflow along the wing lift to the tip while the flow of positive pressure zone under the surface tends to disperse the air flow around the wing tip on the surface of the negative pressure zone. This will form a large vortex at the wing tip extension to the rear, which is called tip vortex, and this is the root of the induced drag generated. To hinder the flow of air turned to the formation of the vortex, or to undermine the vortex structure is an important way to reduce the induced drag.

After F.W. Lanchester putting forward the concept of horseshoe vortex, also proposed to install plates in the tip end to reduce the induced drag. Facts have proved that this structure is indeed to achieve the effect of drag reduction. Later, people continue to research and develop, and thus invented wing tip, and install it in the transport plane, to reduce air resistance. Wing tips on the application of civil aircraft on domestic and aerodynamic design experts received wide attention, the first wing tips are the winglet developed by the NASA Langley Research Center Whitcomb in the 1970s of 20th century, and installed on the tanker in the KC2135, flight test results show that, due to induced drag reduction cause the aircraft to reduce 6.5% of total drag (induced drag reduced 15%), range increased 7.5%. At present, the newly developed aircraft, such as Boeing787 "dream" aircraft and some are operated airliner (Airbus A330, A340, Boeing737-800ER) have adopted wing tips. The drag reduction effect of wing tips is obvious, but the drag reduction effect of wing tip affected by many factors, such as the tilt angle, setting angle, type of winglet, height of winglet, area of winglet and root shoot ratio, etc., it can be seen from the domestic and foreign literature in different aircraft with winglet the drag reduction is also not the same. How to design wing tip to receive more ideal drag reduction effect are the global issues explored by aircraft designers in recent years. Thus, based on the reviews of literature, this thesis designs a winglet and through FLUENT numerical simulation to calculate the drag reduction effect.#p#分頁標題#e#

6.2 Simulation of straight 3D airfoils
6.2.1 Modeling and discretization
Based on NACA airfoil coordinates, it is to determine wing root, and the tip of the coordinates of the turning point to establish an airfoil section, reference ARJ221 wing leading edge sweep angle determining dimensions, such as semi-span and the root tip than the geometric elements through the Solidworks software to build surface models, the chord length at wings wing root Ct = 0.205m, the chord length at turning point Cbp = 0.128m, the chord length at wing tip Ct = 0.0458m, semi-span length b / 2 = 0.553m, the former edge sweep angle χ = 27 °.
Before the simulation calculation, it uses Gambit software to carry out discretization for this model, and the mesh is shown in Figure 1 and Figure 2.

Figure 1 Straight wing

Figure 2 Mesh of flow-field

6.2.2 Computing results
The CFD software FLUENT is widely used for simulation calculation, the results shown in Table 1, in which the lift coefficient CL, drag coefficient CD, lift-drag ratio K are calculated respectively, by the formula CL = L / qS, CD = D / qS, K = CL / CD.
Table 1 Simulated computing results of straight wing
Mach number Ma Angle of attack
α CL CD Lift-drag ratio
K

0.7 0 0.212431 0.0128826 16.48
2 0.442864 0.0190086 23.30
3 0.558562 0.0238826 23.38
4 0.667768 0.0300397 22.23
5 0.776053 0.0393773 19.71
7 0.848098 0.0733607 11.56

6.3 Simulation of 3D airfoils installed winglet
6.3.1 Modeling and discretization
This model, based on a large number of literature and reference dimensions ARJ221 wing design, take the above simulation model as the basic wing of straight wing, at the wing tip to install a winglet, using PRO / E to build surface models, shown in Figure 3 and Figure 4. Similarly, select the type of winglet RAE2822 supercritical airfoil to be able to integrate the basic wing, reducing the generation of interference resistance; the wingspan of winglet is 0.8 times of the chord length of wing tip Ct, the chord length at wing root of winglet Cxr = Ct, the chord length at wing tip Cxt = 0.32 Ct; winglet installation angle 0 °, leading edge sweep angle θ = 38 °, tilt angle γ = 15 ° (leading edge sweep angle, tilt angle, the installation angle defined in Figure 5).

Figure 3 Top view of 3D airfoils installed winglet http://www.ttc-switch.com/dissertation_writing/Engineering/
Figure 4 Left side view of 3D airfoils installed winglet
Figure 5 Schematic diagram of geometric parameters pf winglet

(to be continued…..)