• Proceedings of the KSME Conference
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• 2002.08a
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• pp.771-774
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• 2002

Highly sweep leading edge extensions(LEX) applied to delta wings have greatly improved the subsonic maneuverability of contemporary fighters. In this study, systematic approach by PIV experimental method within a circulating water channel was adopted to study the fundamental characteristics of induced vortex generation, development and its breakdown appearing on a delta wing model with or without LEX in terms of four angles of attack($15^{\circ},\;20^{\circ},\;25^{\circ},\;30^{\circ}$) and six measuring sections of chord length($30{\%},\;40{\%},\;50{\%},\;60{\%},\;70{\%},\;80{\%}$). Sideslip effect in case of the LEX was also studied for two sideslip(yaw) angles($5^{\circ},\;10^{\circ}$) at one angle of attack(20). Distribution of time-averaged velocity vectors and vorticity over the delta wing model were compared along the chord length direction. Quantitative comparison of the maximum vorticity featuring the induced pressure distribution were also conducted to clarify the significance of the LEX existence. Animation presentation in velocity distribution was also implemented to reveal the effect of LEX with wing vortex interaction.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.3
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• pp.1-7
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• 2002

An experimental study was conducted to investigate the effects of leading edge extension(LEX) on the surface prssure distribution over a delta wing in a subsonic wind tunnel. Freestream velocity was 40m/sec and Reynolds number per meter was 1.7x$10^6$ with total pressure of 101Pa and total temperature of 278K. LEX changed the surface pressure distribution on the wing dramatically. Comparing with the results without LEX, the peak of pressure distribution decreased on the front chordwise location but it turned to increase on the rear chordwise location with increase of the angle of attaci. The spanwise gradient of the pressure distribution also increased in the rear chordwise location. Without LEX, the peak of pressure distribution increased and decreased irregularly with increase of the angle of attack at each chordwise location, but LEX made it increased almost linearly with increase of the angle of attack at all of the chordwise locations.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.12
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• pp.9-17
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• 2005

An experimental study of the vortical flow over a yawed delta wing with leading edge extension(LEX) was conducted to investigate the effects of the existence of a centerbody configuration on the flow characteristics of the wing and LEX vortices using off-surface visualization and PIV measurements. The qualitative investigation using these two techniques indicated that the effect of the centerbody existence on the vortex formation was minimal at somewhat low range of angles of attack and sideslip angles. However, the quantitative analysis of the surface pressure measurements revealed the effect of centerbody existence to be prominently increased for the cases with higher angles of attack and sideslip angles. It was also found that the centerbody effect was not significant compared to the effect of sideslip for the present LEX-delta wing configuration.

• 한국가시화정보학회:학술대회논문집
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• 2003.11a
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• pp.39-42
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• 2003

Leading edge extension(LEX) in a highly swept shape applied to a delta wing features the modern air-fighters. The LEX vortices generated upon the upper surface of the wing at high angle of attack enhance the lift force of the delta wing by way of increased negative suction pressure over the surfaces. The present 3-D stereo PIV includes the Identification of 2-D cross-correlation equation, stereo matching of 2-D velocity vectors of two cameras, accurate calculation of 3-D velocity vectors by homogeneous coordinate system, removal of error vectors by a statistical method followed by a continuity equation criterion and so on. A delta wing model with or without LEX was immersed in a circulating water channel. Two high-resolution, high-speed digital cameras$(1280pixel\times1024pixel)$ were used to allow the time-resolved animation work. The present dynamic stereo PIV represents the complicated vortex behavior, especially, in terms of time-dependent characteristics of the vortices at given measuring sections. Quantities such as three velocity vector components, vorticity and other flow information can be easily visualized via the 3D time-resolved post-processing to make the easy understanding of the LEX effect or vortex emerging and collapse which are important phenomena occurring in the field of delta wing aerodynamics.

• International Journal of Fluid Machinery and Systems
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• v.2 no.4
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• pp.439-448
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• 2009

Three inducers were designed to avoid cavitation instabilities. This was accomplished by avoiding the interaction of tip cavity with the leading edge of the next blade. The first one was designed with extremely larger leading edge sweep, the second and third ones were designed with smaller incidence angle by reducing the inlet blade angle or increasing the design flow rate, respectively. The inducer with larger design flow rate has larger outlet blade angle to obtain sufficient pressure rise. The inducer with larger sweep could suppress the cavitation instabilities in higher flow rates more than 95% of design flow coefficient, owing to weaker tip leakage vortex cavity with stronger disturbance by backflow vortices. The inducer with larger outlet blade angle could avoid the cavitation instabilities at higher flow rates, owing to the extension of the tip cavity along the suction surface of the blade. The inducer with smaller inlet blade angle could avoid the cavitation instabilities at higher flow rates, owing to the occurrence of the cavity first in the blade passage and its extension upstream. The cavity shape and suction performance were reasonably simulated by three dimensional CFD computations under the steady cavitating condition, except for the backflow vortex cavity. The difference in the growth of cavity for each inducer is explained from the difference of the pressure distribution on the suction side of the blades.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.7
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• pp.105-112
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• 2002

An experimental study of the vortical flow characteristics around a yawed delta wing with the leading edge extension at high incidence angle is undertaken by upper surface pressure measurements. A special emphasis has been put on analyzing the basic physics of vortical flows, concerning the effects of incidence and sideslip angle on the aerodynamic characteristics of the wing, especially under high angle of attack. The experimental data has been dearly demonstrated the beneficial effect of the LEX vortex on the wing vortex. It leads to an essential stabilization of the wing vortex against its breakdown until at much higher incidence angle under small sideslip. An interesting flow feature is occurrence of the rolling moment reversal at a certain range of angle of attack and sideslip angle.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.109-117
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• 2002

An off-surface flow visualization experiments have been performed to investigate the flow field over a delta wing with the leading edge extension(LEX). The model is a flat wing with $65^{\circ}$ sweepback angle. The free stream velocity is 6.2 m/s, which corresponds to Reynolds number of $4.4\times10^5$ based on the wing root chord. The angle of attack and sideslip angle range from $16^{\circ}\sim28^{\circ}$ and $0^{\circ}\sim-15^{\circ}$, respectively. The visualization technique of using the micro water-droplet and the laser beam sheet enabled to observe the vortical flow structures, which can not be obtained by 5-hole probe measurements. With sideslip angle, the interaction and breakdown of the LEX and wing vortices was promoted in the windward side, whereas, it was suppressed in the leeward side.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1672-1677
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• 2004

Leading edge extension(LEX) in a highly swept shape applied to a delta wing features the modem air-fighters. The LEX vortices generated upon the upper surface of the wing at high angle of attack enhance the lift force of the delta wing by way of increased negative suction pressure over the surfaces. The present 3-D stereo PIV includes the Identification of 2-D cross-correlation equation, stereo matching of 2-D velocity vectors of two cameras, accurate calculation of 3-D velocity vectors by homogeneous coordinate system, removal of error vectors by a statistical method followed by a continuity equation criterion and so on. A delta wing model with or without LEX was immersed in a circulating water channel. Two high-resolution, high-speed digital cameras($1280pixel{\times}1024pixel$) were used to allow the time-resolved animation work. The present dynamic stereo PIV represents the complicated vortex behavior, especially, in terms of time-dependent characteristics of the vortices at given measuring sections. Quantities such as three velocity vector components, vorticity and other flow information can be easily visualized via the 3D time-resolved post-processing to make the easy understanding of the LEX effect or vortex emerging and collapse which are important phenomena occurring in the field of delta wing aerodynamics.

• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.387-392
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• 2013

본 연구에서는 천음속 전투기 무장창 내부의 압력 진동을 제어하기 위해 F-111의 무장창을 2차원 공동(Cavity)으로 모델링하고, EDISON_전산열유체 시스템을 활용하여 공동의 형상 변화에 따라 발생하는 유동 특성을 분석하였다. 최근의 전투기들은 항력 감소와 스텔스 기능을 위해 무기를 기체 안에 내장하는데, 덮개를 열 때 발생하는 공동 형상에 의해 강한 압력 진동이 유발된다. 이러한 진동은 무장창과 주변 기계 장치에 구조적 진동을 일으키고 고장 또는 파괴를 유발하므로, 근본적인 해결책이 필요한 중요한 문제이다. 본 연구에서는 진동의 원인이 되는 전단층(Shear layer) 불안정성을 해결하기 위해 기존에 연구된 형상(Leading edge extension 및 Ramp)과 본 연구에서 새로 제안한 Ramp extension을 적용해 보았다. 그 결과 압력 진동의 원인이 되는 유동 특성이 줄어들고 압력 진동 역시 감소했음을 관찰할 수 있었다.

• Advances in aircraft and spacecraft science
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• v.2 no.3
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• pp.329-343
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• 2015

This study aimed to observe the effect of a novel concept (referred to as the flap extension) implemented on the leading edge of the flap of a three element high lift device. The high lift device, consisting of a flap, main element and slat is designed around an Airbus research profile for sufficient take off and landing performance of a large commercial aircraft. The concept is realised on the profile and numerically optimised to achieve an optimum geometry. Two different optimisation approaches based on Genetic Algorithm optimisations are used: a zero order approach which makes simplifying assumptions to achieve an optimised solution: as well as a direct approach which employs an optimisation in ANSYS DesignXplorer using RANS calculations. Both methods converge to different optimised solutions due to simplifying assumptions. The solution to the zero order optimisation showed a decreased stall angle and decreased maximum lift coefficient against angle of attack due to early stall onset at the flap. The DesignXplorer optimised solution matched that of the baseline solution very closely. The concept was seen to increase lift locally at the flap for both optimisation methods.