• 제목/요약/키워드: Vortex formation

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Effect of Centerbody on the Vortex Flow of a LEX-Delta Wing Configuration (중앙동체가 LEX-삼각날개 형상의 와류에 미치는 영향)

  • Sohn, Myong-Hwan;Chung, Hyoung-Seog
    • 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.

Combustion Characteristics of Non-premixed VIStA Burner in Once-Through-Type Boiler (관류보일러 연소실에서 비예혼합 VIStA 버너의 연소 특성)

  • Ahn, Joon;Kim, Hyouck-Ju;Choi, Kyu-Sung
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.34 no.5
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    • pp.547-552
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    • 2010
  • A modified VIStA (vortex inertial staged air) burner was developed and used in a once-through-type boiler. For safety, the combustion in this burner is of the non-premixed type. An air damper is installed to control the distribution of air to each combustion chamber. The effects of the air-fuel ratio and air distribution on NOx formation were investigated. The newly modified VIStA burner gives NOx reduction effect by maximum 20% in the combustion chamber of a boiler, while it yields more uniform flame than the conventional burner.

Analysis for Combustion Characteristics of Hybrid Rocket Motor (하이브리드 로켓의 연소특성 해석)

  • 김후중;김용모;윤명원
    • Journal of the Korean Society of Propulsion Engineers
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    • v.6 no.1
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    • pp.21-29
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    • 2002
  • Hybrid propulsion systems provide many advantages in terms of stable operation and safety. However, classical hybrid rocket motors have lower fuel regression rate and combustion efficiency compared to solid propellant rocket motor. The recent research efforts are focused on the improvement of volume limitation and regression rate in the hybrid rocket engine. The present study has numerically investigated the combustion processes in the hybrid rocket engine. The turbulent combustion is represented by the eddy breakup model and Hiroyasu and Nagle and Strickland-Constable model are used for soot formation and soot oxidation. Radiative heat transfer is modeled by finite volume method. To reduce the uncertainties for convective heat transfer near solid fuel surface having strong blowing effect, the Low Reynolds number $\kappa-\varepsilon$ turbulent model is employed. Based on numerical results, the detailed discussion has been made for the turbulent combustion processes in the vortex hybrid rocket engine.

A Study on the Visualization of Urban Wind Flow by Using Thermochromic Pigment (열변색성 염료를 이용한 도심 공기 유동 시각화에 관한 연구)

  • Kim, Hong-Seok
    • Journal of the Korea Convergence Society
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    • v.12 no.11
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    • pp.291-299
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    • 2021
  • Recently, due to environmental problems caused by densification and high rise of urban areas, interests in air flow is increasing and appropriate shape and layout design of buildings is required. Therefore, in this study, we intend to propose an experimental method that can observe the air flow around a building using thermochromic pigment. Thermochromic pigments have limitations in observing precise temperature changes due to the characteristic that the color changes only with respect to a specific temperature, but they have the advantages of easy configuration of experimental equipment and short time required for experiments. In this study, the air flow tendencies around a building was examined by performing CFD analysis for a simple model and then compared with the thermochromic experiment results in order to review the usefulness of the proposed experimental method. As a result of the experiment, it was possible to observe the formation of separated flow and vortex region generated by buildings using the charateristics of thermochromic pigment and it was confirmed that the proposed method can be useful for buildings design and urban city planning.

Flow Visualization in Realistic Arterial Bypass Graft Model

  • Singh, Megha;Shin, Se-Hyun
    • International Journal of Vascular Biomedical Engineering
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    • v.3 no.1
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    • pp.1-5
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    • 2005
  • Background: Coronary atherosclerosis artery disease is the leading cause of morbidity and mortality. Coronary artery bypass grafting (CABG) which utilizes the saphenous vein graft, has helped in alleviating the suffering of these patients. Newer techniques are being developed to improve upon the techniques. Still there is significant number of failures, leading to re-grafting or re-vascularization. Some studies have helped in identifying the high and low shear stress regions. Further studies based on their realistic models are required. Material, methods and results: we developed the realistic model of fully blocked right coronary with bypass graft placed at angle of $5^0$ with curvature similar to that of artery. Pulsatile flow of birefringent solution through this model by polarized light was visualized. The images of complete flow field in the model were recorded and analyzed. Regions of high flow disturbances which are prone to further changes are identified. Existence of recirculation in the blocked coronary may initiate new blood-tissue interactions deleterious to bypass graft. Conclusion: Our study shows that by selecting the procedure to place bypass graft at minimum angle with curvature similar to that of artery and smooth sutures may improve the life span of the graft. This study also identified that coronary blocked regions contributing by recirculation flow at the proximal and distal regions of bypass which may require further studies.

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Drag Reduction of a Circular Cylinder With O-rings (O-ring 을 이용한 원주의 저항감소에 관한 실험적 연구)

  • Lim, Hee-Chang;Lee, Sang-Joon
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.2089-2094
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    • 2003
  • The flow around a circular cylinder was controlled by attaching O-rings to reduce drag force acting on the cylinder. Four experimental models were tested in this study; one smooth cylinder of diameter D (D=60mm) and three cylinders fitted with O-rings of diameters d=0.0167D, 0.05D and 0.067D with pitches of PPD=1D, 0.5D and 0.25D. The drag force, mean velocity and turbulent intensity profiles in the near wake behind the cylinders were measured for Reynolds numbers based on the cylinder diameter in the range of $Re_D=7.8{\times}10^3{\sim}1.2{\times}10^5$. At $Re_D=1.2{\times}10^5$, the cylinder fitted with O-rings of d=0.0167D in a pitch interval of 0.25D shows the maximum drag reduction of about 5.4%, compared with the smooth cylinder. The drag reduction effect of O-rings of d=0.067D is not so high. For O-ring circulars, as the Reynolds number increases, the peak location of turbulence intensity shifts downstream and the peak magnitude is decreased. Flow field around the cylinders was visualized using a smoke-wire technique to see the flow structure qualitatively. The size of vortices and vortex formation region formed behind the O-ring cylinders are smaller, compared with the smooth cylinder.

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Simulation of viscous and inviscid rayleigh-taylor instability with surface tension by using MPS

  • Kim, Kyung Sung;Kim, Moo Hyun
    • Ocean Systems Engineering
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    • v.8 no.2
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    • pp.167-182
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    • 2018
  • RTI (Rayleigh-Taylor instability) is investigated by a multi-liquid MPS (Moving Particle Semi-implicit) method for both viscous and inviscid flows for various density differences, initial-disturbance amplitudes, viscosities, and surface tensions. The MPS simulation can be continued up to the late stage of high nonlinearity with complicated patterns and its initial developments agree well with the linear theoretical results. According to the relevant linear theory, the difference between inviscid and viscous fluids is the rising velocity at which upward-mushroom-like RTI flow with vortex formation is generated. However, with the developed MPS program, significant differences in both growing patters and developing speeds are observed. Also, more dispersion can be observed in the inviscid case. With larger Atwood (AT) number, stronger RTI flows are developed earlier, as expected, with higher potential-energy differences. With larger initial disturbances, quite different patterns of RTI-development are observed compared to the small-initial-disturbance case. If AT number is small, the surface tension tends to delay and suppress the RTI development when it is sufficiently large. Interestingly, at high AT number, the RTI-suppressions by increased surface tension become less effective.

In vitro experimental study on flow characteristics of abdominal aorta aneurysm (복부대동맥 동맥류의 유동특성에 관한 in vitro 실험적 연구)

  • Lee, J.P.;Kim, D.S.;Lee, S.J.
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03b
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    • pp.10-12
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    • 2008
  • Hemodynamic features of blood flow in the abdominal aorta aneurysm (AAA) are very important, because they are closely related with the rupture of aneurysm to death. It has been considered that the wall shear stress of blood flows influences the formation, growth, and rupture of AAA. On this account, it is important to understand the flow structure of blood in the aneurysm. In this study, the whole velocity field information inside a typical AAA was measured using an in vitro AAA model under the pulsatile flow condition. The vessel geometry was reconstructed based on the computerized tomography (CT) data of a patient. The AAA model was made by using a rapid prototyping (RP) method, based on the reconstructed vessel geometry. Velocity fields in the AAA model were measured at different pulsatile phases using a PIV (particle image velocimetry) system. As experimental results, a large-scale vortex is formed inside the AAA model and the vortices located near the AAA wall are supposed to increase the local pressure and wall shear stress. In this study, the AAA wall stress found to be was one of the most important governing parameters giving rise to the ruptured aneurysm.

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Characteristics of Near Wake Behind a Circular Cylinder with Serrated Fins (III) - Mechanism of Velocity Recovery - (톱니형 휜이 부착된 원주의 근접후류특성 연구 (III) - 속도회복 메카니즘에 관하여 -)

  • Ryu, Byong-Nam;Kim, Kyung-Chun;Boo, Jung-Sook
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.3
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    • pp.347-356
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    • 2003
  • The characteristics of near wakes of circular cylinders with serrated fins are investigated experimentally using a hot-wire anemometer for various freestream velocities. Near wake structures of the fin tubes are observed using a phase average technique. With increasing fin height and decreasing fin pitch. oscillation of streamwise velocity increases. It file oscillation of lateral velocity decreases. The time averaged V-component velocity distribution of the finned tube is contrary to that of the circular cylinder due to the different strength of entrainment flow. This strength is affected by the distance of (equation omitted) = 1.0 contour lines. (equation omitted) = 1.0 contour line approaches to the wake center line when the fin density is increased. When the distance between (equation omitted) = 1.0 contour lines comes close the shear force should be increased and the flow toward the wake center line can be more strengthened because of the shear force. Factors related to the velocity recovery in the near wake of the finned tube are attributed to tile turbulent intensity, the boundary layer thickness. the position and strength of entrainment process.

Numerical Analysis of Laminar Flows in the Two Dimensional Sector Cavity by Finite Analytic Method in Polar Coordinate System (極座標系 有限解析法 에 의한 2次元 부채꼴 캐비티 의 層流流動 解析)

  • 배주찬;강신영
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.8 no.3
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    • pp.185-194
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    • 1984
  • The finite analytic method is extended to solve the steady two dimensional Navier-Stokes equation of stream functions and vorticity in polar coordinate system. The method is applied to calculate laminar flows in a sector cavity where the motion is induced by the rotation of the outer wall. Numerical solutions are obtained in the range of Reynolds number 0 to 5000 and aspect ratios 0.50, 1.20, 1.60 and 1.92. The finite analytic method is verfied to be accurate and fast convergent at high Reynolds numbers. It is promising as a numerical method of viscous flows and heat transfer. Flows in sector cavities show different flow structures and formation of secondary vortex with aspect ratios and Reynolds numbers in comparison with rectangular cavities.