Research Article Volume 8 Issue 1
Cranfield University, United Kingdom
Correspondence: Amir Zare Shahneha, Centre of Aeronautics, Cranfield University, Cranfield, MK43 0AL, United Kingdom
Received: February 12, 2024  Published: March 1, 2024
Citation: Shahneha AZ. Active injection method for fluidic winglet. Aeron Aero Open Access J. 2024;8(1):3440. DOI: 10.15406/aaoaj.2024.08.00191
Various solutions for the fluidic winglet are proposed to investigate the impact of parameters such as velocity, temperature and injection direction, and slot area for air ejection. This study is based on the replacement to A380 solid winglet. The results reveal that maximising these parameters doesn’t always minimise drag; rather, a balance needs to be found to achieve optimal efficiency. The study demonstrates a potential maximum reduction of 3.81%, often linked with a decrease in lift. The optimal design is a single rectangular slot injecting at 260 m/s, exhibiting lower lift reduction than drag reduction and high efficiency. Thus, currently, there isn’t a significant advantage justifying a paradigm shift for these devices.
Keywords: computational fluid dynamics, aircraft performance, clean wing, winglet, fluidic winglet, wingtip vortices
Air transportation has been grown up by 3.6% from 2019 to 2041, recovering to prepandemic levels by 2023.^{1} This increased demand for aircraft coincides with a growing awareness of emissions in the aeronautical industry, leading to extensive research by manufacturers to develop cleaner vehicles.
To tackle emissions, winglets have been introduced to reduce drag and emissions by mitigating the vortex effect’s thrust requirements. However, these winglets are effective mainly at lowspeed flight, adding weight and parasite drag.
The objectives include studying an alternative approach to reduce wingtip vortices without structural changes. The project involves examining winglet structures, optimising fluidic winglet design through lift and drag coefficient analysis, and evaluating the chosen design’s performance during the cruise phase. The process comprises steps like theory review, preliminary investigation, geometry modeling, and CFD simulations using CATIA and ANSYS Fluent software.
Theory behind wingtip vortices is explained here and the current solutions to reduce their impact will be discussed. It also covers the selection of wing and structural winglet geometries and introduces proposed fluidic winglet slots. A basic design proposal for the fluidic winglet architecture is included.
Wingtip vortices
Aircraft flight relies on lift generated by pressure differences between wing surfaces as air flows at varying speeds. However, at wingtips, air circulates in vortices, creating induced drag. This drag can be reduced using wingtip devices to increase effective wingspan and minimise vortices.
The vortex’s position relative to the wing affects wingspan, impacting lift and drag. Increasing span reduces induced drag. Initial winglets, resembling wingtip fences, prevent air recirculation, eliminating the need for higher angles of attack. Modified winglets, with a winglike shape and tilt, further reduce induced drag and enhance lift, aiding vortex reduction. Studies have explored aircraft fluidic winglets at Mach 0.3, with elongated slots proving most effective.^{2}
Wing geometry selection
The A380800, known for its high passenger capacity and longrange capabilities, is chosen as the base model for the study of wing geometry. This widebody aircraft with four engines has a cruise Mach speed of 0.82 and a cruising altitude of 10,670 meters. While the A380 underwent fewer changes from its original version, one notable modification is the introduction of more efficient ”downlet” winglets, which reduce fuel consumption by 4% compared to the original ”winglet fence” design.^{3}
The study uses the A380’s “clean wing” (without winglets) as the base wing configuration. The winglet model chosen for analysis is the commonly used “winglet fence”. Geometry parameters for both the clean wing and winglets are obtained from the manufacturer document.^{4} The clean wing geometry parameters shows the values of root chord, kink chord and tip chord dimensions when there is no winglet. The span size, sweep angle and dihedral angle for the chosen aircraft are stated in Table 1. The wing profile used is a supercritical one, approximated using the NASA SC(2)0610 model for the wing root.^{5}
Parameter 
Value 
Root chord 
17.67 m 
Kink chord 
13.75 m 
Tip chord 
3.98 m 
Semispan 
39.88 m 
Sweep angle 
35.44º 
Dihedral angle 
5.36º 
Table 1 Clean wing geometry parameters
Design of fluidic winglet
Different fluidic winglet slot geometries have been tested, including a single rectangular slot on the wingtip’s lateral surface, which can be evolved by adding another rectangular slot to the upper surface. This modification increases the area and changes the flow direction. The parameters for these configurations are detailed in Table 2, and their models can be seen in Figure 1.
Parameter 
Value 

Height 
2% 
chord 
Width 
54% 
chord 
Distance from the leading edge 
15% 
chord 
Distance from the wing tip (for the 2 slot configuration) 
3% 
chord 
Table 2 Rectangular slot parameters
Another configuration comprises 10 circular slots with a diameter equal to the height of the rectangular slot, evenly spaced to occupy the same length as the rectangle. The diameter can be adjusted, as explained later. Parameters for this configuration are provided in Table 3.
Parameter 
Value 
Diameter 
2% chord 
Distance from the leading edge 
15% chord 
Slot separation 
3.8% chord 
Table 3 Circular slot parameters
Fluidic winglet architecture
Fluidic winglet architecture is shown in Figure 1. The toplevel conceptual design of the air supply system is presented without detail design. It explores different sources for obtaining air, proposing the use of aircraft engines. The airflow passes through a pressure regulator valve, a shutoff valve, and potentially a heat exchanger before reaching a distributor that feeds it into the wingtip slots.
This section outlines the methodology for modelling various proposed solutions and reference cases, along with the processes for mesh generation and preparing Computational Fluid Dynamics (CFD) simulations to acquire the aerodynamic characteristics of the A380 wing.
Geometry modelling
The wing’s geometry is established using CATIA V5, modelling only half of the wing due to symmetry, Figure 2. This model is then imported into ANSYS Workbench for domain generation and subsequent meshing. The computational domain is symmetrical about the horizontal plane and covers a rectangular area measuring 176.7 m in length and 35.34 m in height. It includes a semicircle originating from the leading edge with a radius of 176.7 m, allowing for angle of attack adjustments without the need for new models. The extension of 10 times the root chord in all directions and applied boundary conditions ensure accurate physics modelling without compressibility effects. Figure 3 shows the CAD models for the different geometries of the fluidic winglets.
Mesh modelling
The ANSYS software is used for meshing the fluid domain, employing a mesh generation algorithm that starts with a surface mesh and then creates a volumetric mesh, Figure 4. The mesh is refined in areas of interest, including the wing surfaces and boundary layers. Specific characteristic dimensions are set for different elements, such as 0.07 m for upper and lower wing surfaces and 0.03 m for leading edges, trailing edges, and the wingtip. Inflation controls consist of 22 layers with specific height and growth ratios. Minimum and maximum element dimensions for the rest of the domain are set at 0.01 and 5 m, respectively, with a growth ratio of 20%.
All these parameters result in a total of 7,229,987 polyhedral elements, with a higher concentration near the surface due to the imposed inflation, which faithfully simulates the phenomena related to wall friction in a realistic manner.
Boundary conditions
The simulation employs a steadystate, pressurebased solver considering gravity. Boundary conditions are set with pressurefarfield boundaries for the upper, lower, and lateral walls, symmetry for the wingcontacted side, and pressurefarfield for curved inflow and rear outflow. Wing and winglet walls are defined as solid, fluidic winglet slots as velocity inlets. Operational conditions include pressure, temperature, air as the medium, density using the ideal gas law, and viscosity via Sutherland’s law. Cruise Mach number is 0.82, with velocity vector direction adjusted for angle of attack. The energy equation and realisable kepsilon turbulence model govern the fluid domain.
This section provides the parameters derived from CFD simulations for comparative aerodynamic analysis of each proposed scenario. This analysis aims to identify the optimal choice among them and evaluate its feasibility by comparing it with the existing solution.
Clean wing
Table 4 the values of aerodynamic coefficients for the clean wing at cruise conditions are tabulated. Figure 5 shows the outcome of CFD simulations for the clean wing under various cruising conditions at angles of attack ranging from 0 to 10 degrees, which the contours are shown in Figure 6. These angles cover a representative range for the cruise phase. It is important to note that the aerodynamic forces are expressed in wind axes, which vary with the angle of attack. The lift and drag coefficients for the reference cases show a linear increase with the angle of attack, as expected. Additionally, the simulations reveal the formation of an oblique shock wave near the wing’s leading edge, with higher angles of attack resulting in a greater velocity vector inclination. At a 10degree angle of attack, the velocity angle causes less change before the oblique shock. However, the presence of this shock wave at 6.25 degrees leads to significant velocity and pressure differences.
AoA [º] 
CL 
CD 
CL/CD 
0 
0.3309 
0.0151 
21.9128 
2.5 
0.5526 
0.0384 
14.3897 
3.75 
0.6573 
0.0559 
11.759 
5 
0.7341 
0.0766 
9.5833 
6.25 
0.8172 
0.0932 
8.7686 
7.5 
0.8831 
0.1124 
7.8568 
10 
1.0281 
0.1487 
6.9134 
Table 4 Aerodynamic coefficients for the clean wing at cruise conditions
Figure 5 Aerodynamic coefficients for the clean wing in cruise conditions.
(a) Lift and drag coefficients for the clean wing.
(b) Aerodynamic efficiency for the clean wing.
Wing with structural winglet
Table 5 shows the percentage difference in the aerodynamic coefficients between the structural winglet and the clean wing in cruise conditions. Fluent has been used to simulate the actual winglet model installed on the clean wing which resulted to a consistent trend similar to the clean wing, with both lift and drag coefficients following a linear progression as the angle of attack changes, as seen in Figure 7. The winglet introduces a reduction in drag and an increase in lift, leading to a substantial improvement in aerodynamic efficiency. The reduction in drag coefficient is more pronounced at lower angles of attack and diminishes at higher angles. On average, these variations range from 4 to 5 percent for angles representative of the cruise phase. Aerodynamic efficiency is notably higher when the wing is positioned more horizontally. At 0 degrees angle of attack, efficiency is approximately 8 times greater than at 10 degrees. The figure also reveals that aerodynamic efficiency decreases parabolically with the angle of attack.
AoA [º] 
LCL (%) 
LCD (%) 
LCL/CD (%) 
0 
10.4216 
5.1255 
16.387 
2.5 
9.2401 
5.0849 
15.0924 
3.75 
7.6289 
4.6901 
12.9252 
5 
7.5248 
4.5203 
12.6154 
6.25 
6.0034 
4.6594 
11.1839 
7.5 
5.2671 
2.6968 
8.1846 
10 
1.7401 
0.5842 
2.338 
Table 5 Percentage difference in the aerodynamic coefficients between the structural winglet and the clean wing in cruise conditions
Wing with fluidic winglet
The study proceeds by simulating various proposals for the implementation of the fluidic winglet, aiming to identify the most optimal solution. Different configurations involving varying injection velocity, temperature, injection angle, and slot parameters are tested. The concept behind modifying these parameters is based on the jet momentum coefficient, which is a product of flight conditions and a form factor. This form factor represents the slot area to wing surface area ratio, while the first component involves the injection velocity relative to the freestream velocity.
Injection velocity
The initial analysis examines the impact of injection velocity, with flight and sound velocities as reference points. The goal is to maximise the ratio of injection velocity to free stream velocity, enhancing the jet momentum coefficient. Simulations are conducted in the range of 250 to 290 m/s with 10 m/s intervals. Two geometries are used: one with a single rectangular slot at the wingtip and another with 10 circular slots matching the dimensions of the rectangular slot, evenly spaced to match its length.
Rectangular slot
In the case of the rectangular slot, all lift coefficients are around 0.8, with higher values for the proposed minimum and maximum injection velocities, peaking at 270 m/s. This trend is reflected in aerodynamic drag as well. Compared to the clean wing, all velocities result in reduced drag coefficients, but they are higher than when using structural winglets. It is important to note that lift production is reduced to varying degrees across all cases.
Aerodynamic efficiency values also decrease across all cases. However, 260 and 290 m/s velocities show positive efficiency values compared to the clean wing. Despite representing the secondhighest drag reduction, 260 m/s results in significantly smaller percentage losses in lift compared to the maximum reduction case.
Table 6 presents the percentage difference in the aerodynamic coefficients between the rectangular slot configuration and the structural winglet and the clean wing in cruise conditions. Figure 8 illustrates the trajectory of air particles exiting the slot, showing an immediate curvature due to the interaction with the wingtip vortex.
VJ [m/s] 
Clean wing 
Structural winglet 

ΔCL (%) 
ΔCD (%) 
ΔCL/CD (%) 
ΔCL (%) 
ΔCD (%) 
ΔCL/CD (%) 

250 
1.975 
0.9908 
0.994 
7.5265 
3.8479 
10.9529 
260 
2.5182 
2.7155 
0.2028 
8.039 
2.0389 
9.8765 
270 
6.358 
2.8065 
3.654 
11.6613 
1.9434 
13.3454 
280 
2.9925 
0.2188 
2.7798 
8.4865 
4.6576 
12.5591 
290 
0.4761 
0.4807 
0.0046 
6.1126 
4.383 
10.0548 
Table 6 Percentage difference in the aerodynamic coefficients between the rectangular slot configuration and the structural winglet and the clean wing in cruise conditions
Round slots
The geometry with circular slots follows a similar trend. Aerodynamic coefficients reach a minimum at 270 m/s, but they are higher than those for the rectangular slot. Aerodynamic efficiencies are also higher for circular slots, but the choice between efficiency and drag reduction depends on comparisons with reference cases. Table 7 shows the percentage difference in the aerodynamic coefficients between the round slots configuration and the structural winglet and the clean wing in cruise conditions.
VJ [m/s] 
Clean wing 
Structural winglet 

ΔCL (%) 
ΔCD (%) 
ΔCL/CD (%) 
ΔCL (%) 
ΔCD (%) 
ΔCL/CD (%) 

250 
0.5061 
0.6469 
0.1417 
6.1409 
4.2086 
9.9315 
260 
0.7646 
0.1877 
0.578 
6.3847 
4.6903 
10.5788 
270 
4.7893 
2.0357 
2.8108 
10.1814 
2.7519 
12.587 
280 
1.8536 
1.1377 
0.7242 
7.412 
3.6938 
10.7103 
290 
2.6642 
0.1453 
2.5226 
8.1767 
4.7347 
12.3277 
Table 7 Percentage difference in the aerodynamic coefficients between the round slots configuration and the structural winglet and the clean wing in cruise conditions
In the case of circular slots, the largest reduction compared to the clean wing is again observed at 270 m/s, but in this instance, the losses in lift are twice as much. When compared to structural winglets, it is evident that the losses in lift are smaller, yet drag is higher in all cases, narrowing the gap in efficiency.
This configuration also exhibits a clockwise circulation, though to a lesser extent, due to the presence of the vortex. Figure 9 shows the streamlines for the injection flow for the circular slot.
Temperature of injection
The effect of varying air temperature on fluidic winglet performance has been investigated, with temperatures ranging from ambient temperature at cruise altitude up to 300K, including 250K and 270K. In Table 8 the percentage difference in the aerodynamic coefficients between the rectangular slot configuration with different injection temperatures and the reference cases in cruise conditions are presented. These temperatures are selected based on estimates of the secondary flow temperature from the engine.
TJ [K] 
Clean wing 
Structural winglet 

ΔCL (%) 
ΔCD (%) 
ΔCL/CD (%) 
ΔCL (%) 
ΔCD (%) 
ΔCL/CD (%) 

218.795 
2.5182 
2.7155 
0.2028 
8.039 
2.0389 
9.8765 
250 
0.0599 
0.8439 
0.9115 
5.6069 
4.002 
9.2391 
270 
2.9118 
1.1552 
1.7771 
8.4103 
3.6754 
11.6572 
300 
4.0287 
0.5947 
3.4546 
9.4639 
4.2634 
13.166 
Table 8 Percentage difference in the aerodynamic coefficients between the rectangular slot configuration with different injection temperatures and the reference cases in cruise conditions
The simulations show that the lowest drag coefficient occurs at ambient temperature, deteriorating as the gas is heated. This trend is inversely proportional to the injection Mach number, with the minimum drag coefficient occurring at the highest injection Mach number.
The highest percentage reduction in drag is observed at 218.795K, derived from the velocity study. However, as the temperature increases, losses in lift become significantly greater, reaching up to 8 times those of drag at 300K. Notably, the scenario involving a temperature of 250K shows a drag reduction of less than 1% and no losses in lift, resulting in an efficiency increase of 0.91%.
Slot area
Modifying the slot geometry to maximise the jet momentum coefficient by increasing the slot area is explored. For the circular slot model, the diameter of each of the 10 slots is increased up to 4% of the tip chord. This adjustment does not alter the trend of the aerodynamic coefficients, which exhibits a minimum at 270 m/s and increases as simulations diverge from this injection velocity. Efficiencies show subtle improvements, but their mean remains relatively stable at around 8.7. The lift coefficient also increases but maintains a mean value within the same range.
Increasing the slot area results in a greater reduction in drag relative to the clean wing, with lift coefficients generally showing a slight increase. This leads to a positive efficiency for the velocity with the lowest drag coefficient.
Rectangular slot
For the rectangular configuration, adjusting the efflux angle leads to the lowest drag coefficient, while only increasing the sweep angle results in a coefficient higher than normal flow. Combining both angle modifications yields the best efficiency but also the most significant reduction in lift, which is counterproductive.
In the case of two rectangular slots, it is similar to altering the injection angles, with the minimum drag coefficient occurring at 270 m/s. The efficiency is 8.6696, and there is a 3.81% drag reduction. The presence of two slots allows for more effective vortex translation due to the generation of two recirculation.
According to Table 9, A380 operating parameters, the analysis of A380 wing airflow has been conducted, Table 10, considering various angles of attack and configurations, including a clean wing and a winglet fence.
Parameter 
Value 
Wing area 
845 m^{2} 
MTOW 
560000 kg 
Cruise altitude 
10670 m 
Cruise speed 
243.1546 m/s 
Thurst 
348 kN 
Range 
14816 km 
Table 9 A380 operating parameters
Source: Jane’s Group UK Limited.^{3}
Parameter 
Value 
Emax 
7.9113 
Vmd 
228.0108 m/s 
ui 
1.0664 
sfc 
2.6940 · 10−6 kg/Ns 
ω 
1.2832 
Range 
17545.8308 km 
Table 10 Performance analysis results
The study explores the potential of replacing structural winglets with fluidic ones by varying parameters like injection velocity, direction, temperature, slot area, and shape.
The efficiency of fluidic winglets relies on careful control of injection parameters. Maximising all variables for high jet momentum coefficient is not the best approach. Moving the vortex farther by increasing dihedral angle reduces drag, but raising the sweep angle alone does not yield the expected improvement.
Doubling the slot area does not double drag reduction; increased injected flow diminishes efficiency. Aerodynamic efficiency improves only for angles below 6.25◦ despite greater drag reduction at higher angles. The optimal fluidic winglet configuration combines substantial drag reduction with a minor lift decrease, achieving a 2.72% reduction and curbing lift losses to 2.52% at an angle of attack of 6.25◦. These are shown in Figure 10.
Despite these findings, local stall potential and the traditional winglet’s superiority at specific angles of attack justify maintaining the existing wingtip devices.
I highly appreciate my colleague Mr Rubio who motivated and engaged in the results.
The authors declare that there is no conflict of interest.
©2024 Shahneha. This is an open access article distributed under the terms of the, which permits unrestricted use, distribution, and build upon your work noncommercially.