By Dan Phillips,2014-12-03 16:47
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    Kemal GÜNDO─×AN

    Faculty of Aeronautics and Astronautics

    Astronautical Engineering

    2. Aerodynamic Systems Abstract-In this article, we will discuss the

    technology behind aerodynamics so that you can 2.1. Fixed-Wing Aircraft see how amazing they really are. The topics

    presented are of general interest, more or less Mc Donnell-Douglas C-17 on a demonstration advanced. There is no mathematics. Large use is flight. The plane is designed for take off and made of graphics, figures, tables, summaries,

    landing on short runways. High lift systems are reference to further reading. The number of

    aerodynamic systems that can be found is required.

    incredibly large. Single components are basic aerodynamic shapes that are generally studied alone: airfoils and wings are among the most well known. Other components are only used as add-

    ons to promote specific aerodynamic

    performances, for example slots, dams, spoilers, fairings, fences, canards, strakes, flaps, vortex generators, splitter plates, tip devices, etc. 1. Introduction

     Aerodynamics is an engineering science

    Figure 1. Fixed-Wing Aircraft concerned with the interaction between bodies and the atmosphere. Technological applications

    2.2. Helicopter and VSTOL aircraft include: General aviation (commercial, cargo, and business aircraft); V/STOL vehicles

     The helicopter and some V/STOL aircraft (helicopters, some military aircraft, tilt rotors);

    belong to the category of rotary-wing powered lighter-than-air vehicles (airships, balloons,

    aircraft. This is a class of vehicles on its own, aerostats); aerodynamic decelerators (parachutes,

    with peculiar aerodynamic and control problems. thrust reversal devices); road vehicles (passenger

    The first helicopters flew many years after the and racing cars, commercial vehicles, high speed

    airplanes. Other V/STOL aircraft feature trains); spacecraft, missiles and rockets, low- to

    complex lifting systems, such as vertical jets and high-speed flight (micro air vehicles to

    tilt rotors. hypersonic waveriders), high altitude flight, human powered flight, unmanned flight, gliders, energy conversion systems (wind and gas turbines); propulsion systems (propellers, jet engines, gas turbines).

     Aerodynamic decelerators include parachutes,

    thrust reversal systems and aerodynamic brakes,

    although only the first ones (broadly called

    parachutes) are generally treated in this category.

    Parachutes have many applications in military

    operations, deployment of payload, rescue

    operations and sports, as shown in the photo at


Figure 2. Helicopter and VSTOL aircraft

    2.3. Lighter-than-Air Systems

     Lighter-than-air are basically balloons and

    airships (or dirigibles). The balloons are the first

    machines that were able to lift from the ground

    with a man on board. Airships came at a much

    later time, and they are usually associated with

    Figure 4. Aerodynamic Decelerators pleasure journeys across the Atlantic or major

    disasters (or both). Either way, lighter-than-air

    2.5. Wind Energy Systems has captured the fantasy of many, not least

    writers of fiction.

     Wind energy systems are among the most

    advanced clean technologies (though not in the

    form showed at right). Many wind turbines are

    now connected to the electric utility networks

    and produce considerable amounts of energy.

    The modern variable- pitch horizontal-axis wind

    turbines (HAWT) are able to work in almost any

    metereological condition.

Figure 3. Lighter-than-Air Systems

    2.4. Aerodynamic Decelerators

    Figure 7. Wind Tunnel Testing

    2.8. Buildings Aerodynamics

     A wide variety of buildings is subject to

    particularly strong aerodynamic forces. These systems include industrial towers, long

    suspension bridges, and off-shore platforms. The Figure 5. Wind Energy Systems

    figure at right shows two industrial towers 2.6. Racing Cars equipped with spirals in order to reduce the

    vortex drag. This technical solution serves to

     Indy CART racing car (Michael Andretti promote turbulent separation around a cylinder, driver). Aerodynamics has a strong impact on thus creating a drag crisis at lower wind speeds. car performance. Engineers find yet new ways to

    produce downforce.

Figure 6. Racing Cars

    2.7. Wind Tunnel Testing

     Wind tunnel testing is one of the most time Figure 8. Buildings Aerodynamics

    consuming, yet effective tools for design and

    research. Tunnel testing is now integrated with 3. Related Topics

    sophisticated CFD methods to save development

    costs. Lift is a force in a direction normal to the

     velocity. It is due to both pressure and viscous

    contributions. The weight of the pressure

    component is generally far more important;

    when the viscous component is effective, it

    works as to reduce the total amount of lift

    obtainable by an aerodynamic system.

3.1. Importance of the Subject

     High lift systems are required in aeronautics

    to produce higher maneuverability, for higher

    endurance under engine failure, for lower take-

    off and landing speed, higher pay-load, for

    aircraft weight constraints, maximum engine

    power limits, etc. High lift systems are of the

    utmost importance in human powered flight,

    unpowered gliding, etc. High lift systems are

    also used (differently) in racing cars and

    competition sailing boats. The picture below Figure 10. Multi-element wing shows the cargo plane C.17 Globemaster with

    high lift system in operation during a slow

     Two boundary layers are confluent when they landing phase.

    develop on different solid surface and come

    together (generally at a different stage of

    development). Confluent boundary layers can be

    identified by studying the local velocity field.

    Flow separation occurs in cove regions because

    of the high curvature associated with locally

    high speed. High speed can also be the reason of

    supercritical regimes in aircraft configurations.

    3.3. Maximum Lift

     The maximum lift obtainable by a single/multi

    element wing (or by more complicated devices)

    is generally attributed to flow separation on the suction side, and on the maximum suction peak.

    The two problems are somewhat dependent. Figure 9. McDonnell Douglas C 17

    Airfoil characteristics that have a strong effect 3.2. Flow Phenomena on the maximum lift coefficient are: camber and

    thickness distributions, surface quality, leading

     Flow phenomena of multi-element wings edge radius, trailing edge angle. CL max also include: wakes from upstream elements merging depends on the Reynolds number. At a fixed with fresh boundary layers on downstream Reynolds number, the operation on the above elements; flow separation in the cove regions; parameters must remove or delay the flow flow separation on the downstream elements, separation, and delay the pressure recovery on especially at high angles (landing the suction side, along with a number of other configurations); confluent boundary layers; high- details.

    curvature wakes; high flow deflection; possible

    supercritical flow in the upstream elements, see 3.4. Prediction of Maximum Lift

    figure below.

     Accurate prediction of the maximum lift

    coefficient for an airfoil or wing is still

    considered an open problem in computational

    aerodynamics. This difficulty is due to the

    approximation of the boundary layer conditions

    at various stages of turbulent transition and

    separation, besides the proper modeling of the

    turbulent separated flows. An empirical formula unpowered. The range of applications in aviation correlating wing CL max of a swept wing to the is discussed below. The data collected in the main geometric parameters of the high-lift figure below have been elaborated from Airbus system was derived at the Research Aeronautical research (Flaig and Hilbig, 1993). Performances Establishment (RAE, UK) in the late 1970s. of the C-17 and the YC-14 have been guessed. More recent work was done at McDonnell-

    3.8. High-Lift Airfoils Douglas (Valarezo-Chin, 1994).

     In order to obtain high lift from an airfoil the 3.5. Vortex Lift

    designer must increase the area enclosed by the

     The lift force from a wing can be augmented pressure coefficient (Cp), that is: the pressure on by appropriate manipulation of separation the lower side must be as high as possible vortices. Basically, this can be done in two ways: (pressure side), the pressure on the upper side with highly swept wings (delta wings) and must be as low as possible (suction side). The strakes. The longitudinal vortex has the effect of latter requirement is in fact the most difficult to shifting the stagnation point on the suction fulfill, because low pressure is created through surface of the wing (Pohlamus, 1971). high speed, and high speed triggers flow

    separation. Flow separation can be limited at

    high speed by turbulent transition.

    3.9. Pressure Distribution

     One idea commonly used in design is to

    control the pressure distribution on the upper

    side as to maintain the flow at the edge of

    separation. The more separation is delayed the

    higher the lift coefficient. This is obtained

    through a flat top and a gradual pressure

    recovery (Stratford recovery). Airfoils designed

    with this approach can exhibit aerodynamic efficiencies L/D of up to 300 !

    Figure 11. Vortex Lift

    3.10. Multi-Element Airfoils

    3.6. High-Lift Systems

     Generally speaking, a multi-element airfoil

     High lift can be produced by aerodynamic consists of a main wing and a number of design of single components, design of entire leading- and trailing-edge devices. The use of systems, integration of already existing systems, multi-element wings is a very effective method ad hoc technical solutions. The most important to increase the maximum lift of an aerodynamic methods are the following: system.

    ; High-lift wing design 4. Conclusions

    ; Multi-element lifting systems

    ; Boundary Layer control In brief, aerodynamic technology meets both our

    ; Propulsive Lift personal and social needs. It makes the daily life

    ; Other Technical Solutions easier by allowing us to connect to the world

    around us. This technology is developing day by 3.7. Powered and Unpowered Systems day. In future it is probably more widespread in

    our life. People are looking forward for the most

     There is a broad classification among all high intelligent technology that would connect the lift systems: that is between powered and technology of aerodynamics.

5. References

    [1]Advanced Topics in Aerodynamics, “World of Aerodynamics”,

    [2] Hoerner SF. Fluid Dynamic Lift, Hoerner Fluid Dynamics, 1965

    [3] Clancy JC. Aerodynamics, John Wiley, New York, 1975.

    [4] AGARD, High-Lift System Aerodynamics, AGARD CP-515, Banff, Oct. 1993

    [5] McCormick BW. Aerodynamics, Aeronautics and Flight Mechanics, John Wiley, New York, 1994. [6] Gratzer, LB. Analysis of Transport Applications for High-Lift AGARD LS-43, 1971.

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