• 제목/요약/키워드: Separated flow

검색결과 728건 처리시간 0.025초

모서리에 펜스를 가진 정방형주의 유체력저감 특성 (Fluid Force Reduction Characteristics of a Square Prism Having Fences on the Corner)

  • 노기덕;김광석
    • Journal of Advanced Marine Engineering and Technology
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    • 제30권3호
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    • pp.389-395
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    • 2006
  • The fluid force reduction of a square prism having fences on the corner was studied by the measuring the drag and lift acting on the prism and by the visualization experiment of the flow around the prism. The height of the fence was 10% of the square width and the range of Reynolds number considered was from $Re=0.9{\times}104$ to $Re=2.1{\times}104$. The drag of the prism was reduced about 6.8% and the amplitude of the lift was reduced by attaching two normal fences on the rear corners of the prism. In this case, the separated flow at the front corners was reattached on the upper and lower sides of the prism and the vortex streets at the wake region were appeared more slowly than that of the prototype prism.

난류박리 및 재부착 유동의 해석을 위한 저레이놀즈수 4-방정식 난류모형의 개발 (A Low-Reynolds-Number 4-Equation Model for Turbulent Separated and Reattaching Flows)

  • 이광훈;성형진
    • 대한기계학회논문집
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    • 제19권8호
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    • pp.2039-2050
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    • 1995
  • The nonlinear low-Reynolds-number k..epsilon. model of park and Sung is extended to predict the turbulent heat transports in separated and reattaching flows. The equations of the temperature variance( $k_{\theta}$ and its dissipation rate(.epsilon.$_{\theta}$ are solved, in concert with the equations of the turbulent kinetic energy(k) and its dissiation rate(.epsilon). In the present model, the near-wall effect and the non-equilibrium effect are fully taken into consideration. The validation of the model is then applied to the turbulent flow behind a backward-facing step and the flow over a blunt body. The predicted results of the present model are compared and evaluated with the relevant experiments.

주기적 통과 후류가 익형위 박리 유동에 미치는 영향 (Effect of periodic wakes on separated flows over a NACA0012 airfoil)

  • 이희강;박태춘;전우평;강신형
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2004년도 춘계학술대회
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    • pp.1619-1624
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    • 2004
  • Experimental study of separated flow over a NACA0012 airfoil is conducted at $Re=2{\times}10^5$ when periodic wakes pass over the airfoil. The wakes are periodically generated by circular cylinders upstream of the airfoil. The measurement of surface pressure and surface visualization at various angles of attack are carried out without and with passing wakes. Without passing wakes, a separation bubble at the leading edge of the suction surface is formed at an angle of attack, found from a local plateau in the streamwise pressure distribution and two distinct lines in the surface flow visualization. With passing wakes, however, the bubble disappears. Owing to passing wakes, the lift increases at high angle of attack and the angle of stall also increases.

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Numerical Analysis of Flow around Rectangular Cylinders with Various Side Ratios

  • Rokugou Akira;Okajima Atsushi;Kamiyama Kohji
    • 한국전산유체공학회:학술대회논문집
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    • 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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    • pp.36-37
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    • 2003
  • Three-dimensional numerical analysis of the flow around rectangular cylinders with various side ratios, D/H, from 0.2 to 2.0 is carried out for Reynolds number of 1000 by using multi-directional finite difference method in multi-grid. The predicted results are well compared with the experimental data. It is found that fluid dynamics characteristics alternate between high pressure mode. and low pressure mode of the base pressure for rectangular cylinder of D/H=0.2-0.6.

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허브 캡 형상에 따른 축류송풍기 성능특성 (Performance Characteristics of an Axial Flow Fan According to the Shape of a Hub Cap)

  • 장춘만;최승만;김광용
    • 한국유체기계학회 논문집
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    • 제9권6호
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    • pp.9-16
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    • 2006
  • Performance characteristics of an axial flow fan having distorted inlet flow have been investigated using numerical analysis as well as experiment. Two kinds of hub-cap, rounded and right-angled front shape, are tested to investigate the effect of inlet flow distortion on the fan performance. Numerical solutions are validated in comparison with experimental data measured by a five-hole probe downstream of the fan rotor. It is found from the numerical results that non-uniform axial inlet velocity profile near the hub results in the change of inlet flow angle. Large recirculation flow upstream the fan rotor for the right-angled hub-cap induces a negative incidence, thus invokes separated flow on the blade surfaces and deteriorates the performance of fan rotor.

Hydraulic Model Experiment on the Circulation in Sagami Bay, Japan (II) - Dependence of the Circulation Pattern on External and Internal Rossby Number in Baroclinic Rotating Model

  • Choo Hyo-Sang;Sugimoto Takasige
    • Fisheries and Aquatic Sciences
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    • 제5권1호
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    • pp.5-20
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    • 2002
  • To investigate the effect of mechanical parameters on the circulation and its fluctuation in Sagami Bay, baroclinic model experiments were carried out by use of a two-layer source-sink flow in a rotating tank. In the experiment, a simple coastal topography with flat bottom was reproduced. The results show that the path of the Through Flow, which corresponds to the branch current of the Kuroshio, depends on external Rossby number (Ro) and internal Rossby number $(Ro^*)$, and divided into two regimes. For $Ro^*\leq1.0$ in which Rossby internal radius of deformation of the Through Flow is smaller than the width of the approaching channel, the current flows along the Oshima Island as a coastal boundary density current separated from the western boundary of the channel. For $Ro^*>1.0$ it changes to a jet flow along the western boundary of the channel, separated from the coast of Oshima Island. The current is independent on both Ro and Ro* in the regime of $Ro^*>1.0,\;Ro\geq0.06$ and $Ro^*\leq1.0,\;Ro\geq0.06$. The pattern of the cyclonic circulation in the inner part of the bay is also determined by Ro and Ro*. In case of $Ro^*\leq1.0$, frontal eddies are formed in the northern boundary of the Through Flow. These frontal eddies intrude into the inner part along the eastern boundary of the bay providing vorticity to form and maintain the inner cyclonic circulation. For $Ro^*>1.0$, the wakes from the Izu peninsula are superposed intensifying the cyclonic circulation. The pattern of the cyclonic circulation is divided into three types; 1) weak cyclonic circulation and the inner anticyclonic circulation $(Ro<0.12)$. 2) cyclonic circulation in the bay $(0.12\leq Ro<0.25)$. 3) cyclonic circulation with strong boundary current $(RO\geq0.25)$.

박막이 부착된 채널내의 2차원 층류유동장에 대한 연구 (Study on Two-Dimensional Laminar Flow through a Finned Channel)

  • 윤석현;정재택
    • 한국전산유체공학회지
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    • 제7권3호
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    • pp.53-59
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    • 2002
  • A two-dimensional laminar flow through a channel with a pair of symmetric vertical fins is investigated. At far up- and down-stream from the fins, the plane Poiseuille flow exists in the channel. The Stokes flow for this channel is first investigated analytically and then the other laminar flows by numerical method. For analytic method, the method of eigen function expansion and collocation method are employed. In numerical solution for laminar flows, finite difference method(FDM) is used to obtain vorticity and stream function. From the results, the streamline patterns are shown and the additional pressure drop due to the attached fins and the force exerted on the fin are calculated. It is clear that the force depends on the length of fins and Reynolds number. When the Reynolds number exceeds a critical value, the flow becomes asymmetric. This critical Reynolds number Re/sub c/ depends on the length of the fins.

잔류내 응집 구조 와류의 생성에 관한 연구 (A Study of Generation of Coherent Vortex in Late Wake)

  • 이승수
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2002년도 학술대회지
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    • pp.443-446
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    • 2002
  • Wake downstream of an object in the stratified flow has been of long-standing interest in fluid dynamics because of its similarity to geophysical flow over topographical terrains and more recently, concerns about the wake left behind a body moving through the ocean thermocline. Decades of studies of geophysical flow have unveiled that the flow downstream of obstacles in stratified flow consists of attached wake and strong internal waves, or separated, fluctuating wake and persistent late wakes, all of which depend on the flow conditions. Among unique and interesting characteristics of the stratified flow past obstacles is the generation of coherent vortex structure in the late wake far downstream of the object. Without the density stratification, the flow field downstream becomes undisturbed after relatively fast diminishing of the near wake. However, no matter how small the stratification is, the flow field downstream self-develops coherent vortex structures even after diminishing of the near wake. This paper present a computational approach to simulate the generation mechanism of the coherent vortex and analysis of the vortical structure.

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박막이 부착된 채널내의 2차원 층류 유동장에 대한 연구 (Study on Two-Dimensional Laminar Flow Through a Finned Channel)

  • 윤석현;정재택
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2001년도 추계학술대회논문집B
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    • pp.545-550
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    • 2001
  • A two-dimensional laminar flow through a channel, on which a couple of symmetric vertical fins are attached, is investigated. The stokes flow for this channel flow is investigated analytically and laminar flow numerically. For analytic solution, the method of eigen function expansion and collocation method are employed. For numerical solution, finite difference method(FDM) is used to obtain vorticity and stream function. From the results, streamline patterns are shown and the pressure drop due to the attached fins is calculated, which depends on the length of fins and Reynolds number. While $Re, streamline pattern is symmetric, a pair of additional asymmetric solutions appear for $Re>Re_c$, where the critical Reynolds number $Re_c$ depends on the length of the fin.

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LES에 의한 관류홴의 전산유동해석 (Computational Flow Analysis of a Cross-Flow Fan by LES)

  • 김장권;오석형
    • 동력기계공학회지
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    • 제14권6호
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    • pp.20-28
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    • 2010
  • The computational flow analysis using LES technique was carried out to investigate the flow characteristics of a RAC chassis consisting of a rear-guider, a stabilizer and a cross-flow fan. The commercial SC/Tetra software was used in this analysis. In view of the results so far achieved, the distribution trends of static pressure and velocity vector of central region except the edges of a CFFan are similar regardless of the number of revolution, and an eccentric vortex exists around the bottom blade of a CFFan. Also, a reverse flow is found in the region between stabilizer and CFFan. Moreover, near the edges of a CFFan, an eccentric vortex is separated to two vortexes. Also these vortexes increase the velocity near a rear-guider, and guide the flow near a rear-guider into stabilizer inlet. Therefore, the reverse flow region is formed in the bottom of a CFFan.