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Kanat-uçkanat etkileşiminin sayısal analizi

Numerical analysis of wing-winglet configuration

  1. Tez No: 101393
  2. Yazar: NURHAK ERBAŞ
  3. Danışmanlar: PROF.DR. A. RÜSTEM ASLAN
  4. Tez Türü: Yüksek Lisans
  5. Konular: Uçak Mühendisliği, Aircraft Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 2001
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 48

Özet

ÖZET 1970'lerin başlarından itibaren uçaklardaki sürüklemeyi azaltmaya yönelik teknoloji askeri ve sivil sahalarda önem kazanmaya başlamıştır. Bu amaçla yapılan çalışmalar, kanat ucuna monteli yüzeylerin kanat uçlarında oluşan girdap yapılarını azalttığını ve yaydığını ortaya koymuştur. Winglet kavramı bu çalışmaların en umut verici olanlarından biridir ve kanadın efektif açıklığını arttıran bir düzenek olarak düşünülebilir. Uçkanat, kanat ucuna monteli bir kaldırma yüzeyi olarak dizayn edilmiştir. Kanat üzerine uygun bir biçimde yerleştirilen uçkanat üzerindeki kaldırma bir yan kuvvet gibi davranır ve akış yönünde bir itki bileşeni oluşturur. Kanat ucunda oluşan girdap akışının içine monte edilmiş küçük bir kanat olan uçkanat sayesinde kanat ucundaki bu girdap yapıları bir ölçüde difüze edilir. Tüm bu olumlu etkilere karşılık hem artan kanat yüklemesi ve hem de uçkanat yüklemesi nedeniyle kanat kökündeki eğilme momentinde bir artış olacaktır ve bu uygun bir düzenek olarak uçkanadın verimliliğini sınırlayabilir. Ağırlık merkezi üzerinde kalan itki nedeniyle de bir burun aşağı moment oluşabilir ve bu da trimleme gerektirmesi dolayısıyla olumsuz etkilere yol açabilir. Uçkanatlar da T-kuyruk veya ok açılı kanat gibi bir dizayn şeklidir. Bir uçaktaki her şey gibi uçkanatlar da performans, kararlılık ve kontrol, yapı, maliyet, ve pazarlama gibi pek çok faktör arasında bir uyuşma gerektirir. Bütün bu faktörler arasında bir uyuşma sağlamak çoğu zaman zordur. Bu nedenle bir uçakta kullanılacak uçkanat tercihi tasarımın optimizasyonuna bağlıdır. Yapılan bu çalışmada uçkanatların uçuş performansına etkilerini incelemek üzere kanat-uçkanat etkileşimi sayısal olarak incelenmiştir. Seçilmiş kanat ve kanat- uçkanat yapıları etrafındaki akım alanının analizi sonlu elemanlar yöntemi kullanılarak Navier-Stokes denklemlerinin çözümü ile elde edilmiştir. VIII

Özet (Çeviri)

NUMERICAL ANALYSIS OF WING-WINGLET CONFIGURATION t i f SUMMARY Since the early seventies, aircraft viscous reduction technology has gained more importance to military and civilian operators. It has been known for a long time that mounting end plates to a wing can reduce and diffuse the vortex structures which are formed by the communication of the high and low pressure regions, across the lifting surface through the wing tips. Altough these tip-mounted surfaces can reduce the induced drag, they also can cause unfavorable interference and viscous effects. The winglet concept is one of the most important of these concepts and is a device to increase the effective span of the wing. In 1970s Richard Whitcomb, one of the NASA aerodynamicist, got his name attached to his two important contributions to aeronautical science: the GA(W) airfoil and the Whitcomb winglet. In 1 976, Whitcomb had documented the effect of winglets upon performance: from four to eight-percent improvement in the lift/drag ratios of several large jet transports. The eight-percent figure applied to an old- technology wing, the KC-135, and five-percent figure became the rule for the improvement to be expected. The aerodynamic forces at the surface of an aircraft may be either tangential to the surface or normal to the surface, and both contribute to the total drag on the body. These important contributors to the total drag are the folio wings: ? Skin-friction drag due to the viscosity of the air, ? Lift-induced drag due to the conserved circulation developed around the wings, ? Pressure drag due to the open seperation in the afterbody and other regions, ? Interference effects between aerodynamic components, ? Wave drag due to compressibility effects at near-sonic flight conditions, ? Miscellaneous effects such as roughness effects and leakage. The greatest contribution arises from turbulent skin-friction drag. The next most significant contribution arises from the lift-induced drag and this, added with the friction drag, accounts for about 85 percent of the total aircraft drag. Winglet designed to reduce the induced drag of an aircraft is a smal wing mounted in the vortex flow at the wing tip. The lift on the winglet acts as a sideforce and, with proper mounting of the winglet to the wing tips, winglet will have trust component in the stream direction (Figure 1). IXWINCH, KT TOTAL WINULET LIFr THRUST COMPONENT Figure 1. Winglets for drag reduction [1] The structure of the vortices is some what diffused due to the winglets. However, there will be an increase in wing root bending moment due to both the increased wing loading and winglet loading and this may limit the utility of winglets. A nose down pitching moment can also occur due to the above-center thrust location and this can lead to a trimdrag penalty. In addition there are attendant increases in other forms of drag such as skin-friction drag and interference drag at the junction region. Designed as a lifting surface mounted at the wing tip, winglet can produce a gain in induced efficiency at a small cost in weight, viscous drag, and compressibility drag [3]. The geometry of a winglet is primarily determined by the toe-in (or toe out) angle, cant angle, leading-edge sweep angle, and the chord and aspect ratio of the winglet, as shown in Figure 2. Cant angle l'Yonl view leading-edge! sweep angle Side view Plan view Toe-in angle Figure 2. Three views of a winglet [2] For the best performance, proper design of the winglets is critical and requires some specific design details as follows[l]:? For good supercritical performance, the winglet should be tapered and swept aft. It should be mounted behind the region of lowest pressure of the main wing to minimize interference effects. ? Some outward cant is desirable and helps to minimize interference at the junction. ? Smooth fillets should be used between the wing tip and the winglet, or smaller drag-reduction benefits may result. ? Some toe-out of the winglet is needed due to the inflow angles at the wing tip. This is also desirable since it reduces the likelihood of winglet stall during sideslip. ? Although the drag reduction increases with winglet span, it is less than linear. Therefore, the optimal winglet height must be a trade-off between the improved aerodynamics and the increased moments due to the larger moment arms. ? In principle, winglets can be mounted above or below the wing, but operational requirements and ground clearances favor upper mounts. A smaller winglet below and ahead of the main winglet is desirable for preventing stall on the main winglet at high lift conditions. Besides drag reductions, winglets have other favorable characteristics which might be important. Among these are the better control of the spreading and dispersal of particulates behind agricultural aircraft and improved hangar and ground maneuvering clearances for large aircraft. In certain integrated aircraft designs they can also act as aircraft control surfaces. To obtain the optimum design of a winglet requires several investigation of numerous winglets which have different design features. For such a design approach, using a wind tunnel as an experiment tool may be too costly and/or time consuming. Also, it may be impossible to set up an experiment which correctly scales the actual flow. Fortunately a modern designer is provided with the facilities of a virtual wind tunnel. It is the Computational Fluid Dynamics, commonly known under the acronym 'CFD', which gives the power of a wind tunnel and the ease of modeling the region of interest. Grid generation is a very important aspect of solving computational fluid dynamics problems where a suitable discretization method is used, a method of approximating the differantial equations by a system of algebric equations for the variables at some set of discrete locations in space and time. In this study, a commercial preprocessor (MSC/Patran) is used for the grid generation. In this study first a coarse and a fine grid around a simple winglet-mounted wing which is once studied is generated by MSC/Patran. Both of these grids are used in low Reynolds number computations of Re=1000. Another application is a comparasion between a wing and a winglet-mounted wing. Various grids are generated around the wing and the winglet-mounted wing. In this thesis, first a general introduction to the winglet concept is given. Then the governing equations of the unsteady flow of the incompressible viscous fluids and the finite element method used for the numerical solution are given. Results are presented in the form of graphics. Finally, some conclusions and recommendations aven.XI

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