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The Cfd Analysis Of Winglets Engineering Essay

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In this interim report, I am going to talk about the topic of my project, aims of the project, tasks performed, project timeline, discussions and conclusions. The topic of my project is CFD ANALYSIS OF WINGLETS. When I decided to choose this project I had no idea about the winglets. Therefore, I have read a lot of about winglets. I needed to learn enough about them such as what they are, where they are used, how winglets work, why they are used in many aircrafts, how many types of winglets are there, which is the most used, winglets benefits…etc. These questions will be answered later.

On section 2 aims and deliverables, I talk about what I could do in my project to be a brilliant project and what I have to do to achieve it.

On section 3, I will attempt to explain what the winglets are, for that I post several images. Different types of winglets and their internal structure will be studied on the second and third point. On the next point, I talk about winglets dimensions and winglet airfoil. For that, an image is shown with a classic winglet design and three winglets airfoil are shown too. On point 3.5, winglets technology is explained. Finally, blended winglets (are the most popular winglets, as you can check later) features and benefits are explained. This is the section 3, analysis of tasks.

A Gantt chart will be shown to check project timeline and progress to date. My interim report finishes with discussion and conclusions.

2. AIMS AND DELIVERABLES

With my project, I will demonstrate winglets are tools that improve the aircraft's performance. For that, I will attempt to demonstrate winglets reduce the aerodynamic drag so fuel consumption goes down. I will analyze a wing with and without winglet and the creation of a vortex near at the wingtip could be checked. My knowledge and skills are not very deep in fluent and gambit so I need to improve them. Thus, this improvement will also be an important objective. Three winglets airfoil will be analyzed in Gambit and Fluent and their results will be discussed with my supervisor. These winglets airfoil are shown on section 3.4.2.

3. ANALYSIS OF TASKS

3.1 WINGLET DEFINITION

Winglets are vertical extensions of wingtips that improve an aircraft's fuel efficiency and cruising range. Designed as small airfoils, winglets reduced the aerodynamic drag associated with vortices that develop at the wingtips as the airplane moves through the air. By reducing wingtip drag, fuel consumption goes down and range is extended. Aircraft of all types and sizes are flying with winglets. From single-seat hang gliders and ultralights to global jumbo jets. Some aircraft are designed and manufactured with sleek upturned winglets that blend smoothly into the outer wing sections.

The concept of winglets originated with a British aerodynamist in the late 1800s, but the idea remained on the drawing board until rekindled in the early 1970s by Dr. Richard Whitcomb when the price of aviation fuel increased.

Fig.3.1.1: Vortex wingtip with and without winglet.

Winglets reduce wingtip vortices, the twin tornados formed by the difference between the pressure on the upper surface of an airplane's wing and that on the lower surface. High pressure on the lower surface creates a natural airflow that makes its way to the wingtip and curls around it.

Since the 1970s, when the price of aviation fuel began spiralling upward, airlines and aircraft manufactures have looked at many ways to improve the operating efficiency of their aircraft. Winglets have become one of the industry's most visible fuel saving technologies and their use continues to expand.

Their main functions are: improved wing efficiency translates to more payload, reduced fuel consumption (about 4% in many flights when the distance to crossing is more than 1800 Km.), and a longer cruising range that can allow an air carrier to expand routes and destinations.

The figures, reproduced below, are showing two images about winglets.

Fig.3.1.2: The figure reproduced above shows winglets.

Fig.3.1.3: Winglets in cars.

With winglets aerodynamic drag goes down, so these components are often used in car industry. Winglets are used in cars of high range or even in formula 1.

3.2 TYPES OF WINGLETS

In general any wingtips that not end the wing simply horizontally are considered as some kind of a winglet. Even though in strictly technical terms Wingtip Fences are not real extensions of the wing, and Raked Wingtips do not have a vertical part, they are still widely considered as winglet variants. We can distinguish three types of winglets: wingtip fences, blended winglets and raked wingtips. The differents types of winglets are explained showing various images and commenting on the aircraft in which they are used.

3.2.1 WINGTIP FENCE

They are a special variant of winglets that extend both upward and downward from the tip of the wing. Preferred by European plane-maker Airbus, it is featured on their full product range (except the A330/340 family and the future A350). The Airbus A300 was actually the first jet airliner to feature this kind of solution by default, but it was a very small version of the tool. Provided that most of the Airbus planes (including all A320 family jets) feature such wingtip fences, this may be the most seen and most produced winglet type. Even the new Airbus A380 double-decker features wingtip fences.

Fig.3.2.1.1: Airbus Winglets as seen from the outsider.

Fig.3.2.2.2: Airbus Winglets as seen from onboard.

3.2.2 BLENDED WINGLETS

They are knowing as the real "Winglets". They are the most popular winglet type, leveraged by Airbus, Boeing, Embraer and Bombardier but also by Russian Tupolev and Iljushin. Blended winglets were first introduced on the McDonnel Douglas MD-11 aircraft in 1990 with launch customer Finnair (it also features a smaller winglet at the bottom side of the wing). In contrast to Airbus who applies the wingtip fences by default on most of their aircraft (and the winglets on the A330/340 family), blended winglets are considered by Boeing for example as an optional extra feature on their products, except for the Boeing 747-400. For some of the older Boeing jets (737 and 757) such blended winglets have been offered as an aftermarket retrofit, these are the newer, tall designs and do not connect to the tip of the wing with a sharp angle, but with a curve instead. These winglets are popular among airlines that fly these aircraft on medium/long haul routes as most of the real fuel savings materialize while cruising. Longer flights mean longer cruising, thus larger fuel savings. And they also server as marketing surface for airline logos or web addresses usually.

141 ship sets have been pre-sold already as the forecasted fuel avings range around 4%-6% for medium/long-range flights. Airbus earlier tested similar blended winglets designed by Winglet Technology for the A320 series, but determined that their benefits did not warrant further development and they stayed with the wingtip fences instead. Aviation Partners Boeing claims that winglets on 737s and 757s have saved a collective 1.2 billion gal. of fuel since they were introduced and 11.5 million tonnes of CO2 while reducing those types' noise footprint by 6.5%. It has sold winglets to 140 airlines and 95% of all 737NGs are fitted with them.

Fig.3.2.2.1: Blended Winglets on Several Aircraft Types.

3.2.3 RAKED WINGTIPS

They are the most recent winglet variants (they are probably better classified as special wings), where the tip of the wing has a higher degree of sweep than the rest of the wing. They are widely referred to as winglets, but they are better described as integrated wingtip extensions as they are (horizontal) additions to the existing wing, rather than the previously described (near) vertical solutions. The stated purpose of this additional feature is to improve fuel economy, climb performance and to shorten take off field length. It does this in much the same way as "traditional" winglets do. In testing by Boeing and NASA, raked wingtips have been shown to reduce drag by as much as 5.5%, as opposed to improvements of 3.5% to 4.5% from conventional winglets. Airliners to use raked wingtips: Boeing 747-8, Boeing 767-400ER, Boeing 777 (-200LR; -300ER; and freighter versions) plus the new Boeing 787 Dreamliner and the Airbus A350. The 747-8, the 787 and the A350 will have special, new kind of wings, which do not have a separate winglet, but have raked, and blended wingtips integrated without a sharp angle between the wing and the winglet.

Fig.3.2.3.1: Raked Wingtips on the new Boeing 787 and Airbus A350.

3.2.4 WING VORTEX ELIMINATOR

This is a special type of winglet. A type exists of winglet that is capable of neutralizing the vortex, this winglet is named Wing Vortex Eliminator, and consists of a pipe that canalizes the air mass that happens for the top of the wing, redirecting and avoiding that the air masses of the lower surface and upper surface come together of turbulent form.

Fig.3.2.4.1: Wing vortex Eliminator.

The following figure shows a summary with the types of winglets and different

aircrafts where they are used.

Fig.3.2.1: Types of winglets.

3.3 INTERNAL STRUCTURE OF A WINGLET

Fig.3.3.1: Winglet structure.

The winglets are aerodynamic surfaces, with an inner structure usually two beams (they are horizontal beams that cover the wings from the insert to the end), a pair of ribs (beams perpendicular to the previous ones to stiffen the structure), and two cloths or outer flat plates that bear the way out. Depending on the type of aircraft or manufacturer, these structures are half-metal or half metal composite material. Are embedded in the wing tip, integrating in their structure, so that only removed if a problem is detected or corrosion.

3.4 WINGLETS DIMENSIONS AND WINGLET AIRFOIL

3.4.1 DIMENSIONS

When I have to built winglets for CFD analysis these dimensions will not be enough. I do not include more images because they are very big. I will need to check websites where I can see general dimensions of an aircraft such as Boeing's or Airbus' websites.

Fig.3.4.1.1: Classic winglet design.

3.4.2 WINGLET AIRFOIL

The winglet airfoil must be design with the following criteria in mind:

* To minimize drag at low CL conditions. 

* To design the winglet airfoil to be tolerant of low Re. 

* To maximize tolerance to negative alpha.

The images, reproduced below, show several winglets airfoil.

Fig.3.4.2.1: winglet airfoil PSU-90-125WL.

Fig.3.4.2.2: winglet airfoil E197.

Fig.3.4.2.3: winglet airfoil MH 201.

These winglets airfoil will be used in CFD analysis.

3.5 WINGLETS TECHNOLOGY

Total pressure of an incompressible fluid is the sum of static and dynamic pressure. The laws of kinetic energy govern dynamic pressure. The difference in air pressure between the lower and upper surfaces of a wing causes the air to escape around the wingtip, which reduces the available lift or the aerodynamic drag increases. The motion of the air rushing around the wingtip causes a vortex to form near the wingtip. The tip vortices cause upwash and downwash air currents that alter the direction of the free stream flow around the wing.

Fig.3.5.1: Vortex at the wingtip.

When an air mass is crossed by a wing that air mass is separated into two streams: a stream passes through the bottom of the wing and the other stream passes through the top of the wing. Both meet at the trailing edge. However, in the wing tip the same phenomenon, but unlike the previous two air flows converge before reaching the trailing edge creating a turbulence so-called vortex. 

A vortex is created near the wingtip. Thus, it is necessary put a barrier at the wingtip. This is the concept of winglets. Winglet attracted to him the vortex and it is deflected far over the wing. Therefore, the aerodynamic drag is reduced.

The winglet has a tip, just like a wing, so it also produces a tip vortex, albeit a much weaker one. The winglets tip vortex is located far above the airflow over the wing, thus it has a little influence on the airflow over the main wing. They look like vortex diffusers.

The installation of well-designed winglets can improve the performance of an aircraft, however, the following aspects are critical:

1) The design must be strongly customized to each new configuration;

2) Winglets introduce additional weight;

3) They increase the wing root bending moment;

4) Efficiency is proportional to the lift coefficient;

5) They can alter the aerodynamics in critical regions (ailerons);

6) Winglets are expensive.

3.6 FEATURES AND BENEFITS

3.6.1 REDUCED ENGINE MAINTENANCE COSTS

Better climb performance also allows lower thrust settings, thus extending engine life and reducing maintenance costs.

REDUCING THRUST WILL:

Slow EGT deterioration, which prolongs on-wing life between engine shop visits.

Reduce fuel flow deterioration, which results in lower fuel burn.

Lower maintenance costs by increasing time between shop visits (longer on-wing life).

Takeoff thrust typically reduced by 3%.

Cruise thrust typically reduced by 4%.

Graphic 3.6.1.1

3.6.2 LOWER BLOCK FUEL

Winglets lower drag and improve aerodynamic efficiency, thus reducing fuel burn. Depending on the missions you fly, blended winglets can improve cruise fuel mileage up to 6 percent, especially important during a time of rising fuel prices. They are saving a minimum of 4% on fuel and up to 6% on our longer flights.

FUEL SAVINGS FOR CONVERTED FLEET

As of mid-October 2006, Aviation Partners and Aviation Partners Boeing have equipped over 1,400 aircraft with Blended Winglets. They conservatively estimate that these aircraft are saving:

146,550,000 gallons per year.

401,507 gallons per day.

16,729 gallons per hour.

279 gallons per minute.

4.6 gallons per second.

POTENTIAL ANNUAL FUEL SAVINGS PER AIRPLANE

737-700

Up to 110,000 gallons

737-800

Up to 130,000 gallons

737-900

Up to 150,000 gallons

737-300

Up to 100,000 gallons

757-200

Up to 300,000 gallons

767-300ER (PD Study)

Up to 500,000 gallons

Table 3.6.2.1: this table shows fuel saved in Boeing´s airplane.

3.6.3 HIGHER INITIAL & OPTIMAL CRUISE ALTITUDES

Winglet equipped airplanes can achieve higher operational altitudes than the baseline non-winglet equipped airplane. This results in the following:

Winglet equipped airplanes can achieve higher initial altitudes eliminating the requirement for initial level-off altitudes.

Winglet equipped airplanes can achieve approximately 1,200 ft higher optimal altitudes than non-winglet equipped airplanes.

Graphic 3.6.3.1

3.6.4 PERMANENT FUEL PRICE HEDGE

With uncertainty in fuel supplies and the continuing increase in demand, the potential for higher fuel prices cannot be ignored.

Consider the average customer for the following:

 

Average Yearly Fuel Savings

(gallons per year)

Additional Savings

for a $0.10 Increase

in Price per Gallon

737-700

Up to 110,000 gallons

Up to $11,000 per year

737-800

Up to 130,000 gallons

Up to $13,000 per year

737-900

Up to 150,000 gallons

Up to $15,000 per year

737-300

Up to 100,000 gallons

Up to $10,000 per year

757-200

Up to 300,000 gallons

Up to $30,000 per year

767-300ER

(PD Study)

Up to 500,000 gallons

Up to $50,000 per year

Table 3.6.4.1

3.6.5 INCREASED PAYLOAD / RANGE CAPACITY

The addition of Aviation Partners Blended Winglets has demonstrated drag reduction in the 5 to 7% range that measurably increases range and fuel efficiency. In addition, the Blended Winglets allow commercial aircraft to take off from higher, hotter airports with increased payload. This enables you to fly farther nonstops or to complete shorter missions with greater payloads and fuel reserves.

3.6.6 ENVIRONMENTALLY FRIENDLY

Winglets offer the opportunity not only to improve an airplanes operation performance but also its environmental performance.

Airport Noise Levels can be dramatically affected with the installation of Winglets:

Noise-affected area on takeoff reduced by 6.5 %.

Take-off and approach certified noise levels are lowered.

Emissions:

Lower fuel burn also equates to reduced emissions.

Up to a 6% reduction in CO2 and as much as a 8% reduction in NOx is possible.

3.6.7 IMPROVED TAKEOFF PERFORMANCE

By allowing a steeper climb, winglets pay off in better takeoff performance, especially from obstacle-limited, high, hot, weight-limited, and/or noise-restricted airports. Performance Improved climb gradients increase 737-800 allowable takeoff weight (TOW).

SOME EXAMPLES INCLUDE:

- Chicago-Midway: ~1,600 lb additional TOW.

- Lanzarote (Canary Islands): ~3,500 lb additional TOW.

- Albuquerque, Denver, and Salt Lake City: ~4,400 lb additional TOW.

4. PROJECT TIMELINE

With the Gantt chart, you can see the tasks done to date and the future tasks. I will try to follow it and I hope to finish my project on April.

As you can see, on the first weeks of my project I have been finding out information about winglets. The first two weeks, I answered two questions; what are the winglets? and what are their main function?. About tenth of November, I started to collect images of winglets and began to understand winglets technology. The following week, winglet design was studied. From my presentation, I made these tasks; airfoil winglets, types of winglets and features and benefits.

From now, I have to do CFD analysis of winglets. I will start in 2-D with winglet airfoil and will finish in 3-D. Winglet airfoil will be imported into a data file to a gambit where the mesh geometry and boundary types will be created. Finally, a file .msh will be created in gambit and it will be exported to fluent where the winglet airfoil will be analyzed. The procedure is the same in 3-D, however the geometry of the aircraft will be set up in Solid Edge or Catia V5 and it will be exported to gambit.

5. DISCUSSION AND CONCLUSIONS

As you have witnessed in this interim report the winglets improve the performance of an aircraft by reducing the aerodynamic drag and therefore the fuel consumption decreases. However, when designing winglets we should take into account aspects such as they are expensive or they increase the wing root bending moment. There are also people who think the winglets are unnecessary and break up the aesthetic of the plane. There are several types of winglets and the blended winglet is the most popular winglet type. Features and benefits of blended winglet have been discussed (http://www.aviationpartnersboeing.com/index.html).

In these first few weeks of work I have tried to to collect enough information about winglets and I reported about how they work, because they break the vortex generated at the wingtip vortex and how it is generated. I am looking forward to start my analysis with fluent and gambit, but my limited knowledge in CFD, stopped me. I feel I am ready to start working with fluent and gambit since these programs have been explained in class successfully.


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