• Title/Summary/Keyword: 원봉

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Local Convective Mass Transfer and Flow Structure Around a Circular Cylinder with Annular Fins (환상핀이 부착된 원봉 주위의 3차원 박리 유동구조 및 물질전달 특성 해석)

  • 박태선;성형진
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.6
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    • pp.2132-2146
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    • 1991
  • Extensive experiments were carried out to investigate the mass transfer and flow structures around a circular cylinder with annular fins in crossflow. The naphthalene sublimation method was employed to measure the circumferential and longitudinal variations of mass transfer from the circular cylinder between annular fins and H is the height of the fin from the cylinder surface. A remarkable enhancement of mass transfer due to the horseshoe vortices was observed near the corner junction between the annular fin and circular cylinder. The present results indicate that the local circumferential Sherwood number shows the higher values on the front stagnation point. The maximum augmentation of mass transfer rate at the center of cylinder is found near L/H-0.15 due to the separation bubble along the annular fins. The secondary flows, which are the corner vortices V2 and V3 near the end wall of the annular fin, are fairly predicted from the distributions of local Sherwood number in the spanwise direction. The average Sherwood number of overall surface at L/H=0.15 is larger 2.0 times than that of without annualr fins. The correlations of total average mass transfer rate with L/H and Re$_{L}$ can also be obtained.d.

Feedback Control of a Circular Cylinder Wake with Rotational Oscillation (주기적 회전을 이용한 원봉 후류의 되먹임 제어)

  • Baek, Seung-Jin;Seong, Hyeong-Jin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.9
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    • pp.1234-1240
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    • 2002
  • A new feedback control law is proposed and tested for suppressing the vortex shedding from a circular cylinder in a uniform flow. The lift coefficient ( $C_{L}$) is employed as a feedback control signal and the control forcing is given by a rotational oscillation of the cylinder. The influence of the feedback transfer function on the $C_{L}$ reduction is examined. The main rationale of the feedback control is that a feedback control forcing is imposed at a phase which is located outside the range of lock-on. By applying the feedback control law, $C_{L}$ is reduced significantly. Furthermore, the reduction mechanism of $C_{L}$ is analyzed by showing the vortex formation modes with respect to the forcing phase.e.ase.e.

Feedback Control of a Circular Cylinder Wake with Rotational Oscillation (주기적 회전을 이용한 원봉 후류의 되먹임 제어)

  • Baek, Seung-Jin;Sung, Hyung-Jin
    • Proceedings of the KSME Conference
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    • 2001.06e
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    • pp.265-270
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    • 2001
  • This study presents a feedback control methodology for suppression of the vortex shedding from a circular cylinder in a uniform flow. A rotational oscillation is applied as a controlled forcing and the lift coefficient ($C_L$) is used as a feedback signal. A feedback control concept is made based on the phase relation between the rotation velocity and $C_L$ at 'lock-on', The phase between the forcing and the vortex formation is changed $180^{\circ}$ from the phase of enhancing the lock-on state. This concept is examined by solving the Van del Pol equation. The results are satisfactory.

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Experimental Study of Mass Transfer on a Film Cooled Cirular Cylinder Surface (막냉각되는 원봉 표면에의 물질전달에 관한 실험적 연구)

  • 이준식;이택식;이상우
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.5
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    • pp.1756-1762
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    • 1991
  • 본 연구에서는 막냉각되는 터빈블레이드에서의 열전달 계수를 측정하기 위하 여 열전달과 물질전달의 상사관계를 이용하였다.터빈블레이드의 선단을 다른 연구 에서와 마찬가지로 원봉으로 모사하였고, 원봉의 표면에 위치하고 있는 1열의 분사홀 로부터 제트가 분사될 때 분사홀 근처 및 그 하류에서의 물질 전달계수를 측정하기 위 해 나프탈렌승화법을 이용하였다. 분사홀 열의 위치를 정체점에서 하류방향으로 이 동시키면서, 물질전달계수의 변화를 연구하였고, 분사율(M=.rho.$_{j}$ U$_{j}$ /.rho.$_{\infty}$ U$_{\infty}$)의 영향도 고찰하였다.

Feedback Control of a Circular Cylinder Wake with Rotational Oscillation (주기적 회전을 이용한 원봉 후류의 되먹임 제어)

  • Lee S. B.;Baek S.-J.;Sung H. J.
    • 한국전산유체공학회:학술대회논문집
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    • 2005.04a
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    • pp.51-56
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    • 2005
  • A new feedback control system based on system identification is proposed and preliminarily tested on Van der Pol equation which has a similar characteristic to circular cylinder. The same principle is applicable to circular cylinder in a uniform flow for suppresing the vortex shedding. The feedback controller is designed to impose feedback signal at the phase which is located outside the range of lock-on. The lift coefficient (CL) is employed as a feedback signal and the control forcing is given by a rotational oscillation of the cylinder. By applying the feedback control system, the lift coefficient is reduced.

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Numerical simulation of the flow behind a circular cylinder with a rotary oscillation (주기적으로 회전하는 원봉 주위의 후류에 관한 수치적 연구)

  • Baek, Seung-Jin;Seong, Hyeong-Jin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.22 no.3
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    • pp.267-279
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    • 1998
  • A numerical study was made of flow behind a circular cylinder in a uniform flow, where the cylinder was rotationally oscillated in time. The temporal behavior of vortex formation was scrutinized over broad ranges of the two externally specified parameters, i.e., the dimensionless rotary oscillating frequency (.110.leq. $S_{f}$.leq..220) and the maximum angular amplitude of rotation (.theta.$_{max}$=15 deg., 30 deg. and 60 deg.). The Reynolds number (Re= $U_{{\inf}D}$.nu.) was fixed at Re=110. A fractional-step method was utilized to solve the Navier-Stokes equations with a generalized coordinate system. The main emphasis was placed on the initial vortex formations by varying $S_{f}$ and .theta.$_{max}$. Instantaneous streamlines and pressure distributions were displayed to show the vortex formation patterns. The vortex formation modes and relevant phase changes were characterized by measuring the lift coefficient ( $C_{L}$) and the time of negative maximum $C_{L}$( $t_{-C}$$_{Lmax}$) with variable forcing conditions.s.tions.s.s.s.

원봉의 일방향 응고과정에 대한 수치해석

  • 김한상;김민수;노승탁;박용조;김학민
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.4
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    • pp.1033-1041
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    • 1990
  • 본 연구에서는 금속의 응고과정에 수반되는 고체와 액체의 밀도차에 의한 체 적수축을 고려하여 원봉내에서의 일방향 응고과정에 대한 수치해석을 하였다. 상변 화면에서 체적수축에 의한 중력방향으로의 액상 전체운동(bulk motion)과 원봉의 인출 속도 및 주형벽면에서의 경계조건이 금속내부의 온도분포와 상경계면의 이동속도에 미 치는 영향에 대해 연구하였다.

EFFECTS OF FIN SPACING ON CONVECTIVE HEAT TRANSFER FOR A CIRCULAR CYLINDER WITH ANNULAR FINS (환상핀이 부착된 원봉에서 핀 간격에 따른 대류열전달 해석)

  • Park, Tae Seon;Kim, Chang Ha
    • Journal of computational fluids engineering
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    • v.19 no.2
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    • pp.1-7
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    • 2014
  • This study is to analyze the local convective heat transfer for a circular cylinder with annular fins. The relation between wall heat transfer and three-dimensional flow is investigated for different distances of annular fins. Depending on the fin spacing, the flow structure is strongly changed by the variation of horseshoe vortices. As the fin spacing increases, the heat transfer rate is maximized at a certain condition. This is clearly obtained as the Reynolds number increases, and it is closely related to the development of horseshoe vortices.

Heat Transfer Enhancement in a Circular Rod Using Mixing Vane (Mixing Vane에 의한 단일봉에서의 열전달 촉진)

  • Lee, Sang-Sub;Yoo, Seong-Yeon;Kim, Byeong-Chae;Kim, Eun-Kee;Lim, Duck-Jae;Chung, Chang-Kyu;Kim, Seoug-Beom
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.408-413
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    • 2003
  • Naphthalene sublimation technique is used to investigate the average and local heat transfer from the circular rod, and to determine the average and local heat transfer from the circular rod with and without square wing type mixing vane in axial flow. The experiments are performed for a circular rod and flat plate with and without mixing vane in wind tunnel. In comparison with flat plate and circular rod in axial flow, averaged Nusselts number is increased 2 times as the increase of Reynolds number with mixing vane. Longitudinal vortex induced by square wing type has the stronger vortex strength, so square wing type vortex generator shows an effect further in downstream.

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Numerical Prediction of Turbulent Flow over a Circular Cylinder (원봉주위의 난류유동에 대한 수치해석)

  • Park T. S.
    • Journal of computational fluids engineering
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    • v.7 no.1
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    • pp.20-27
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    • 2002
  • Flow over a circular cylinder is studied numerically using a turbulence model. Based on the κ-ε-f/sub μ/ model of Park and Sung[6], a new damping function is used. The efficiency of the strain dependent damping function is addressed for vortex-shedding flows past a circular cylinder. The mean velocity and Reynolds stresses are compared with available experimental data at Re/sub D/= 3900. Also, the computational results for the Strouhal number are evaluated at several Reynolds number. The predictions by κ-ε-f/sub μ/ model are in good agreement with the experiments.