• The KSFM Journal of Fluid Machinery
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• v.8 no.6 s.33
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• pp.47-54
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• 2005

An oscillating foil can produce a driving force through the generation of a reversed $K\'{a}rm\'{a}n$ vortex street, and it can be expected to be a new highly effective propulsion system. A simple pitching foil model was made and it was operated within a water channel. The wake formation behind a pitching foil was visualized and unsteady fluid forces were measured using a 6-axis force sensor based on force and moment detectors. We have been examined various conditions such as reduced frequency, amplitude and pivot point in NACA 0010. The results showed that thrust coefficients increased with a reduced frequency. We also presented the experimental results on the characteristics of a pitching foil at various parameters.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2006.06a
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• pp.279-280
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• 2006

In the present study the flow fields around pitching foils have been visualized by using a Schlieren method with a high speed camera in a wind tunnel at low Reynolds number regions. It has been observed that small vortices are shed discretely from the leading and trailing edge and that they stand in line on the integrated streakline of separation shear layer. By counting vortices in the VTR frames it was clarified that the number of vortex shedding from the leading and trailing edge during one pitching cycle strongly depends on the non-dimensional pitching rate.

• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.554-559
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• 2016

본 논문은 EDISON CFD를 사용하여 스포일러가 장착된 무미익 BWB UCAV에 대하여 이차원 유동해석을 수행하였다. 무미익 형상은 일반적인 항공기보다 롤과 요 방향의 안정성과 조성성에 있어 불리한 특징을 갖는데 특히 이 착륙 시 고 받음각의 영역에서 발생하는 Pitch-up 현상이 항공기 안정성에 문제를 야기한다. 수직 미익 부재와 pitch-up 현상으로 인한 BWB형상의 UCAV가 지니는 단점을 보완하기 위해서 스포일러가 장착된 형상이 적용되기도 한다 본 연구에서는 윗면과 아랫면에 스포일러가 장착된 경우에 대해 전산유동해석을 수행하였다. 해석결과 윗면의 스포일러는 양력의 감소와 항력의 증가를 야기했으며, 아랫면의 스포일러는 양력과 항력을 모두 증가시켰다. 피칭모멘트의 경우 아랫면의 스포일러가 저받음각에서 안정성을 증가시켰다.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.2
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• pp.152-158
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• 2007

Most of experimental visualizations and numerical results on the flow field separated form a leading edge around an unsteady foil show a continuous streakline from the leading edge and large reverse flow between the streakline and the suction surface. However, they have not exactly clarified yet the dynamic behavior of vortices separated from the leading edge because separation around an unsteady foil is very complicated phenomenon due to many parameters. In the present study the flow fields around pitching foils have been visualized by using a Schlieren method with a high speed camera in a wind tunnel at low Reynolds number regions. It has been observed that small vortices are shed discretely from the leading and trailing edge and that they stand in line on the integrated streakline of separation shear layer. By counting vortices in the VTR frames it was clarified that the number of vortex shedding from the leading and trailing edge during one pitching cycle strongly depends on the non-dimensional pitching rate. Futhermore the vortices moving up to the leading edge on the suction surface of the pitching foil are visualized. They play an important role to balance the number of vortex shedding from both edges.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.2 s.245
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• pp.117-125
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• 2006

In the present study the unsteady forces acting on the pitching foils such as a flat plate, NACA0010, NACA0020, NACA65-0910 and BTE have been measured by using a six-axis sensor in a circulating water tunnel at a low Reynolds number region. The unsteady characteristics of the dynamic drag and lift have been compared to the quasi-steady ones which are measured under the stationary condition. The pitching motion is available for keeping the lift higher after the separation occurs. Especially, the characteristics of the dynamic lift are quite different from the quasi-steady one at high pitching frequency regions. As the pitching frequency deceases, the amplitude of the dynamic lift becomes closer to the quasi-steady one. However, the phase remains different between the steady and unsteady conditions even at low pitching frequencies. On the other hand, the dynamic drag is governed strongly by the angle of attack.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.2
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• pp.109-117
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• 2020

A structured grid system can be efficiently constructed by applying the patched-grid algorithm that alleviates many constraints of the conventional structured grid system. Three approaches were applied to case 4 of the EFD-CFD workshop: delta wing-cylindrical body shape to solve the existing grid generation problems and verify the results by comparing them with experimental data. Surface pressure distributions slightly differed from the experimental data at high angles of attack. The slope variation of the pitching moment with Mach number is analyzed and the variation can be explained with the tuck under phenomenon. In the supersonic region, the bow shock waves in front of the shape expand the region generating lift up to the rear of the configuration. Also, the tendency of the pitching moment with both Mach number and angle of attack was analyzed by comparing the positions of the center of pressure and the center of gravity.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.6
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• pp.1-7
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• 2003

In this study, steady/unsteady aerodynamic characteristic for three dimensional symmetric wing was investigated numerically using Vortex Panel Method. This program utilized linearly varying vortices in x and y directions distributed on the wing surface and was applied to the incompressible potential. flow around a three dimensional wing Separation and deformation of the wake are not considered. The comparison between NACA Airfoil Data and the computed results showed excellent agreement. πus method was applied to unsteady wings undergoing both sudden pitch-up and constant rate pitching motion. In the unsteady flow analysis, a formation and a time-dependent locations of Starting Vortices are considered and the effect of Starting Vortices on aerodynamic characteristic of the wing was calculated. The present method can be extended to apply for more complicated cases such as pitching, flapping and rotating wing analysis.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.3
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• pp.224-231
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• 2015

An experimental study on aerodynamic coefficients of a lambda wing configuration was performed at the low speed wind tunnel of Agency for Defense Development. The main purpose of this study was to investigate the effects of sideslip angle on various aerodynamic coefficients. In the case of $0^{\circ}C$ sideslip angle, nose-up pitching moment rapidly increases at a specific angle of attack. This unstable pitching moment characteristic is referred to as pitch break or pitch up. As the sideslip angle increases, the pitch break is found to be generated at a higher angle of attack. Rolling moment is found to show similar behavior pattern to 'pitch break' style with angle of attack at non-zero sideslip angles. This trend gets severer at greater sideslip angles. Yawing moment also shows substantial variation of the slope and the unstable directional stability with sideslip angles at higher angles of attack. These characteristics of the three moments clearly implies the difficulty of the flight control which requires efficient control augmentation system.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.1
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• pp.1-9
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• 2018

Lambda wing type Unmanned Combat Aerial Vehicle(UCAV) which adopts Blended Wing Body(BWB) has relatively less drag and more stealth performance than conventional aircraft. However, Pitching moment is rapidly increased at a specific angle of attack affected by leading edge vortex due to leading edge sweep angle. Wind tunnel testing and numerical analysis were carried out with UCAV 1303 configuration on condition of 50 m/s of flow velocity, $-4^{\circ}{\sim}28^{\circ}$ of the range of angle-of-attack. The effect of wing twist for longitudinal stability at the various angles of attack was verified in this study. When negative twist is applied on the wing, Pitch-break was onset at higher angle of attack due to delayed flow separation on outboard of the wing. On the other hand, pitch-break was onset at lower angle of attack and lift-to-drag ratio was increased when positive twist is applied on the wing.

• Journal of Korean Medical classics
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• v.13 no.2 s.17
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• pp.44-56
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• 2000

장개빈(張介賓)(1563-1640, 호시경악(號是景岳))시명말의학가이계승김원대의학전통적인물(是明末醫學家而繼承金元代醫學傳統的人物). 타재(他在) 류경도익(類經圖翼), 의역의(醫易義) 주장'의역동원'이논증의학여역학지회통성(主張'醫易同源'而論證醫學與易學之會通性). 타이성리학이론내연구의학(他以性理學理論來硏究醫學). 인이피칭위'유의'(因而被稱爲'儒醫'). 타광범지연구유가급제자백가지후(他廣範地硏究儒家及諸子百家之後), 이(以) 황제내경(黃帝內經) 여(與) 난경 위주(難經 爲主). 종합의가학설(綜合醫家學說). 타이(他以) '양상부족음본무여'지관념내설명인체내음양상태('陽常不足陰本無餘'之觀念來說明人體內陰陽狀態) 이반박주진형지자음론(而反駁朱震亨之滋陰論). 인이주장'부양억음'급'태극시명문'적학설(因而主張'扶陽抑陰'及'太極是命門'的學說). 타재(他在) 의역의(醫易義) 이부양억음내해설병리(以扶陽抑陰來解說病理). 관어태극-명문적론의야수성리학태극개념적영향(關於太極-命門的論議也受性理學太極槪念的影響). 단시(但是), 소위(所謂) '조원찬화'('調元贊化') '기사회생'적의학목적시속어도교양생론('起死回生'的醫學目的是屬於道敎養生論). 관어차점(關於此點), 연피칭위유의적성리학의가야병부예외(連被稱爲儒醫的性理學醫家也竝不例外). 일반인위 황제내경 시재전국 한대초기형성적(一般認爲 黃帝內經 是在戰國 漢代初期形成的). 야인위기의학체계반영저황로사상여음양오행론(也認爲其醫學體系反映著黃老思想與陰陽五行論). 장개빈수재성리학적립장내주장자기적이론(張介賓雖在性理學的立場來主張自己的理論). 단시대폭지접수도가급도교립장(但是大幅地接受道家及道敎立場). 타재(他在) 류경도익(類經圖翼), 태극도론(太極圖論), 이태극성위만물생명적근원(以太極成爲萬物生命的根源). 동시언급도도가여역위(同時言及到道家與易緯). 재장개빈(在張介賓), 태극시상통어도가발생론적개념(太極是相通於道家發生論的槪念). 야상통어태극적개념(也相通於太極的槪念). 재(在) 유경(類經), 섭생(攝生) 내간(來看). 타제요로장이외(他除了老莊以外). 우인용송대이후내단사상가강백단 이도순등적주장(又引用宋代以後內丹思想家强伯端 李道純等的主張), 인이전개자기적이론(因而展開自己的理論). 필자시위(筆者視爲), 장개빈재의학적양생방면상접수료이'성명쌍수'위기적송대이후내단사상(張介賓在醫學的養生方面上接受了以'性命雙修'爲基的宋代以後內丹思想). 병차타이연단적관점내이해부양억음(竝且他以煉丹的觀點來理解扶陽抑陰). 신위유의적장개빈능구장유도량자회통위일조의학체계적의거재어역학.(身爲儒醫的張介賓能구將儒道兩者會通爲一條醫學體系的依據在於易學). 장개빈재천인상응관념지하(張介賓在天人相應觀念之下), 용이음양변화지기구내변증천인관계(用以陰陽變化之機構來辨證天人關係). 재타적이론(在他的理論), 천지시속어 역(天地是屬於 易), 인시속어 의(人是屬於 醫), 단시양자귀위동일양적일리(但是兩者歸爲同一樣的一理). 재'원취제물(在'遠取諸物), 근취제신'적관점내강(近取諸身'的觀點來講), 타장'근취제신'적도리취어의학(他將'近取諸身'的道理取於醫學). 환유'원취제물'적도리취어역학(還有'遠取諸物'的道理取於易學), 인이모구귀납성일개원리(因而謀求歸納成一個原理). 타장자연현상적원리내재어인지생명(他將自然現象的原理內在於人之生命), 종여차정체적각도내간(從如此整體的角度來看). 가이설의학시상통어역학적(可以說醫學是相通於易學的). 역학대인여자연간적탐구(易學對人與自然間的探求), 비교측중어이론성(比較側重於理論性). 반이의학이역학이론위자(反而醫學以易學理論爲資). 관어자연여인지생명진일보지진행교구체성적연구(關於自然與人之生命進一步地進行較具體性的硏究). 총지(總之), 장개빈통과태극음양론(張介賓通過太極陰陽論), 부분유 도이참재'생명'적립장(不分儒 道而站在'生命'的立場), 광범지접납유도양가(廣範地接納儒道兩家). 유차(由此) 아문가이여도장개빈의서적가치병부한어의학가치(我們可以如道張介賓醫書的價値竝不限於醫學價値). 장개빈의서제시유 도량가가이회통어"생명사상"적철학상가능성(張介賓醫書提示儒 道兩家可以會通於"生命思想"的哲學上可能性).