• Wind and Structures
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• 제31권1호
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• pp.15-20
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• 2020

The aircraft industry supports aviation by building aircraft and manufacturing aircraft parts for their maintenance. Fuel economization is one of the biggest concerns in the aircraft industry. The reduction in specific fuel consumption of aircraft can be achieved by a variety of means, simplest and more effective is the one to impose minor modifications in the aircraft main wing or the parts which are exposed to the air flow. This method can lead to a reduction in aerodynamic resistance offered by the air and have a smoother flight. The main objective of this study is to propose geometric design modifications on an existing aircraft wing which acts as a vortex generator and it can reduce the drag and increase lift to drag ratio, leading to lower fuel consumption. The NACA 2412 aircraft wing is modified and designed. Rigorous flow analysis is carried out using computational fluid dynamics based software Ansys Fluent. Results show that saw tooth modification to the main wing shows the best aerodynamic efficiency as compared to other modifications.

• International Journal of Fluid Machinery and Systems
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• 제2권3호
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• pp.215-222
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• 2009

Jets issuing through small holes in a wall into a freestream has proven effective in the control of flow separation. This technique is known as the vortex generator jet (VGJs) method. If a precursor signal of separation is found, the separation control system using VGJs can be operated just before the onset of separation and the flow field with no separation is always attained. In this study, we measured the flow field and the wall static pressure in a two-dimensional diffuser to find a precursor signal of flow separation. The streamwise velocity measurements were carried out in the separated shear layer and spectral analysis was applied to the velocity fluctuations at some angles with respect to the diffuser. The pattern of peaks in the spectral analysis changes as the divergence angle increases over the angle of which the whole separation occurs. This change in the spectral pattern is related to the enhancement of the growth of shear layer vortices and appears just before the onset of separation. Therefore, the growth of shear layer vortices can be regarded as a precursor signal to flow separation.

• 대한기계학회논문집
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• 제19권3호
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• pp.834-845
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• 1995

An experimental study is made in a nearly two-dimensional 90.deg. curved duct to investigate the effects of interaction between streamline curvature and mean strain on turbulence. The initial shear at the entrance to the curved duct is varied by an upstream shear generator to produce five different shear conditions ; a uniform flow (UF), a positive weak shear (PW), a positive strong shear(PS), a negative weak shear (NW) and a negative strong shear(NS). With the mean field data of the case UF, variations of the momentum thickness, the shape factor and the skin friction over the convex(inner) surface and the concave (outer) surface are scrutinized quantitatively in-depth. It is found that, while the pressure loss due to curvature is insensitive to the inlet shear rates, the distributions of wall static pressure along both convex and concave surfaces are much influenced by the inlet shear rates.

• 한국전산유체공학회지
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• 제20권4호
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• pp.21-27
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• 2015

Flow field around the KRISO 3600TEU container ship is computed using a surface generated based on interpolations of station lines, which are given in a body plan of the ship, without using any CAD program. An interpolation method is suggested based on inscribed circles to generate curves between two neighboring station lines. The interpolated surface is saved in a STL format to use the snappyHexMesh utility of the openfoam. Computed resistance of the ship is compared with experimental and other computational results and the effects of the interpolation of neighboring station lines on the computed resistance are investigated. The suggested method is applied to calculate the flow field around a submarine with appendages. The surface triangulations for the hull and the appendages are generated without consideration of each other, then those surface triangulations are simply combined to provide a grid generator with the body boundary. The junctures of the hull and the appendages are identified automatically during the grid generation procedure. Tip vortex is captured, which travels downstream from the tip of the appendages.

• 한국항공우주학회지
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• 제50권11호
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• pp.747-754
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• 2022

유체진동기에서 분출되는 초음속 진동제트를 이용하여 충격파에 의한 경계층 박리유동을 제어하는 실험적 연구가 이루어졌다. 유체진동기의 위치와 제어압력의 변화가 경사충격파에 의하여 발생되는 경계층 박리유동의 특성에 미치는 영향이 관찰되었고, 이를 위하여 고속 슐리렌, 표면유동가시화, 벽압력 측정, 그리고 정밀 피토관 측정 기법이 적용되었다. 본 연구의 초음속 진동제트의 박리유동 제어 특성은 공기제트 와류를 이용한 기존 제어기법과 정량적으로 비교 분석되었다.

• Advances in aircraft and spacecraft science
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• 제10권3호
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• pp.203-222
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• 2023

The detonation combustion is a supersonic combustion process follows on shock wave oscillations in detonation tube. In this paper numerical studies are carried out combined effect of blockage ratio and spacing of obstacle on detonation wave propagation of hydrogen-air mixture in pulse detonation combustor. The deflagration to detonation transition of stoichiometric (ϕ=1)fuel-air mixture in channel has been analyzed for effect of blockage ratio (BR)=0.39, 0.51, 0.59, 0.71 with spacing of 2D and 3D. The reactive Navier-Stokes equation is used to solve the detonation wave propagation mechanism in Ansys Fluent platform. The result shows that fully developed detonation wave initiation regime is observed near smaller vortex generator ratio of BR=0.39 inside the combustor. The turbulent rate of reaction has also a great significance role for shock wave structure. However, vortices of rapid detonation wave are appears near thin boundary layer of each obstacle. Finally, detonation combustor demonstrates the superiority of pressure gain combustor with turbulent rate of reaction of 0.6 kg mol/m3 -s inside the detonation tube with obstacle spacing of 12 cm, this blockage enhanced the turbulence intensity and propulsive thrust. The successful detonation wave propagation speed is achieved in shortest possible time of 0.031s with a significance magnitude of 2349 m/s, which is higher than Chapman-Jouguet (C-J) velocity of 1848 m/s. Furthermore, stronger propulsive thrust force of 36.82 N is generated in pulse time of 0.031s.

• 에너지공학
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• 제14권4호
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• pp.241-247
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• 2005

3열 정렬형 관군 배열에서 3열의 'common flow up'과 'common flow down' 형상의 와류발생기를 부착하여 와류발생기에 의한 열전달 촉진과 압력강하를 비교하였다 선행 연구자들이 제안한 'common flow down' 형상의 와류발생기는 와류발생기가 없는 휜-관군에 비해 열전달 촉진은 $10\%{\~}25\%$ 향상되었고, 압력강하는 $20\%{\~}35\%$ 증가하였다. 'common flow up' 형상의 와류발생기의 경우 후연 수평거리(${\Delta}y$)를 변화시키면서 평가하였다. 와류발생기는 삼각형과 사각형 형상을 적용하였다. 후연 수평거리(${\Delta}y$)가 5mm이고 삼각형의 'common flow up' 형상의 와류발생기가 정렬형 관군에서 설치될 때 Reynolds수(유로 높이의 배를 기준으로)가 $300{\~}2700$ 범위에서 열전달촉진은 10까지 향상하였고, 동시에 압력강하는 $8\%{\~}15\%$ 감소하였다. 삼각형 와류발생기가 부착된 휜-관군의 성능이 상대적으로 작은 압력강하 때문에 사각형 와류발생기가 부착된 휜-관군의 성능보다 좋게 나타났다.

• 전자공학회논문지CI
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• 제45권3호
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• pp.160-174
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• 2008

본 논문에서는 삼차원 메쉬 모델의 광학성 정보를 부호화하기 위한 새로운 방법을 제안한다. 색상 정보, 법선벡터 정보 및 텍스처 정보의 부호화 효율을 개선하기 위하여 제안한 방법들은 기하학 정보와 연결성 정보를 이용하여 광학성 정보를 예측 부호화한다. 먼저 연결성 정보를 이용하여 광학성 정보의 부호화 순서를 결정하고, 이를 통해 얻어진 인접한 꼭지점들의 기하학 정보를 이용하여 광학성 정보를 예측 부호화한다. 색상 정보는 기하 예측기를 사용하여 부호화하고, 법선벡터 정보는 거리 균등화기와 최적화 평면 발생기를 적용하여 부호화하며, 텍스처 정보는 삼차원 메쉬 모델 분석기, 텍스처 좌표 분석기, 텍스처 영상 재배열기와 예측 부호화기를 이용하여 부호화한다. 색상 정보는 현재 꼭지점과 인접한 꼭지점 사이에 기하학 정보를 고려하여 인접한 꼭지점들의 색상 정보의 가중치 합으로 계산할 수 있다. 또한 법선벡터 정보는 현재 꼭지점의 법선벡터를 예측하기 위해서 이등변 삼각형의 특성을 이용한 거리 균등화 기법과 상호연관성이 높은 인접한 꼭지점의 특징을 이용한 최적화 평면을 개발했으며 효율적으로 삼차원 좌표를 압축하기 위해서 구면 좌표계와 6-4분할 양자화 방법을 사용하였다. 마지막으로 텍스처 정보는 부호화 순서에 따라 텍스처 영상의 조각을 재배열하여 텍스처 좌표를 불연속성을 제거한다. 다양한 삼차원 메쉬 모델들에 대해 실험한 결과를 살펴보면 제안된 압축 방법이 이전의 방법보다 개선된 부호화 효율을 제공하였다.

• 한국해양공학회지
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• 제10권3호
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• pp.138-152
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• 1996

Many studies of heat transfer on the swirling flow or unswirled flow in a abrupt pipe expansion are widely carried out. The mechanism is not fully found evidently due to the instabilities of flow in a sudden change of the shape and appearance of turbulent shear layers in a recirculation region and secondary vortex near the corner. The purpose of this study is to obtain data through an experimental study of the swirling flow and heat transfer downstream of an abrupt expansion in a circular pipe with uniform heat flux. Experiments were carried out for the turbulent flow nd heat transfer downstream of an abrupt circular pipe expansion. The uniform heat flux condition was imposed to the downstream of the abrupt expansion by using an electrically heated pipe. Experimental data are presented for local heat transfer rates and local axial velocities in the tube downstream of an abrupt 3:1 & 2:1 expansion. Air was used as the working fluid in the upstream tube, the Reynolds number was varied from 60, 00 to 120, 000 and the swirl number range (based on the swirl chamber geometry, i.e. L/d ratio) in which the experiments were conducted were L/d=0, 8 and 16. Axial velocity increased rapidly at r/R=0.35 in the abrupt concentric expansion turbulent flow through the test tube in unswirled flow. It showed that with increasing axial distance the highest axial velocities move toward the tube wall in the case of the swirling flow abrupt expansion. A uniform wall heat flux boundary condition was employed, which resulted in wall-to-bulk temperatures ranging from 24.deg. C to 71.deg. C. In swirling flow, the wall temperature showed a greater increase at L/d=16 than any other L/d. The bulk temperature showed a minimum value at the pipe inlet, it also exhibited a linear increase with axial distance along the pipe. As swirl intensity increased, the location of peak Nu numbers was observed to shift from 4 to 1 step heights downstream of the expansion. This upstream movement of the maximum Nusselt number was accompanied by an increase in its magnitude from 2.2 to 8.8 times larger than fully developed tube flow values.