• Title/Summary/Keyword: Reattachment

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Heat/Mass Transfer and Flow Characteristics Within a Film Cooling Hole of Square Cross Sections (I) - Effects of Blowing Ratio and Reynolds Number - (정사각 막냉각홀 내부에서의 열/물질전달 및 유동 특성 (I) - 분사비 및 레이놀즈 수 효과 -)

  • Kang, Seung-Goo;Rhee, Dong-Ho;Cho, Hyung-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.7
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    • pp.927-936
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    • 2002
  • An experimental study has been conducted to investigate the heat/mass transfer characteristics within a film cooling hole of square cross-section for various blowing ratios and Reynolds numbers. The experiments have been performed using a naphthalene sublimation method and the flow field has been analyzed by numerical calculation using a commercial code. A duct flow enters into a film cooling hole in a cross-direction. For the film cooling hole with square cross-section, it is observed that the reattachment of separated flow and the vortices within the hole enhance considerably the heat/mass transfer around the hole entrance region. The heat/mass transfer on the leading edge side of hole exit region increases as the blowing ratios decrease because the main flow induces a secondary vortex. Heat/mass transfer patterns within the square film cooling hole are changed little with the various Reynolds numbers.

Aerodynamic Heating Analysis of Spike-Nosed Missile (스파이크가 부착된 유도탄의 공력 가열 해석)

  • Jung Suk Young;Yoon Sung Joon;Byon Woosik;Ahn Chang Soo
    • Journal of the Korea Institute of Military Science and Technology
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    • v.7 no.3 s.18
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    • pp.21-29
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    • 2004
  • Numerical analysis of aerodynamic heating for KPSAM is performed using aerodynamic heating model suitable to KPSAM, which has complex flow field resulting from the spike attached to the dome, such as large separation area and the strong shock/boundary layer interaction region around reattachment point on the dome. The aerodynamic heating model is validated and modified through the comparison between the flight test measurement and the thermal analysis results. TFD temperature sensors are installed on the dome to measure surface temperature during the flight. Computation results, obtained from the heat transfer analysis on the sensors, agree well with flight test data. The aerodynamic heating model provides heat transfer rate into surface as a boundary condition of unsteady 1D/axisymmetric thermal analysis on the missile structure. The axisymmetric thermal analysis using FLUENT is more versatile than the 1D analysis and can be applied to the heating problem related with complex structures and multi-dimensional heat transfer problems such as prediction of temperature rise at contact surface of different materials.

On Vortical Structures in Near-Wake Region of a Cubic Obstacle Mounted on a Channel Wall (채널 내에 부착된 정육면체 장애물 후류에서의 Vortex 구조에 대하여)

  • Hwang, Jong-Yeon;Yang, Gyeong-Su
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.12
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    • pp.1861-1868
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    • 2001
  • Vortical structures in the near-wake region of a cubic obstacle are studied using numerical simulation. We consider flow between two parallel plates with a cube mounted on one of the plates. In the turbulent near-wake region of the flow, coherent structures such as hairpin vortices are found. Quasi-periodic behavior of the hairpin vortices is noticed; its dimensionless frequency at Re=1,000 is about 0.82 which is consistent with the result of Elavarasan of et al.'s experiment [Fluid Dyn. Research, 2000, 27] although their geometry is somewhat different from on. In the case of Re=3,500, the dimensionless frequency of the hairpin vortex is about 1.60. It is observed that the translating speed of the head of the hairpin vortex is lower than the streamwise mean velocity at that location. In the vicinity of the lower plate downstream of the cube, various length scales are identified thus less coherent. However, it is noticed that the vortical structures become gradually elongated downstream of the new reattachment.

Large-Scale Vertical Structure in Separated and Reattaching Turbulent flow over a Backward Facing Step (후향계단 난류 박리재부착 유동에서의 대형와의 구조)

  • Ahn, Seung-Kwang;Lee, In-Won;Sung, Hyung-Jin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.12
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    • pp.1674-1680
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    • 2002
  • An experimental study was made of a large-scale vortical structure over a backward-facing step. The Reynolds number based on the step height was R $e_{H}$ =33,000. To recognize the large-scale vortex, three components of velocity were measured. The measurements were performed in the recirculation zone (x/H=4.0) and the reattachment zone(x/H=7.5). To measure the wall pressure fluctuations in a turbulent flow over a backward-facing step, a 32-channel microphone array was installed beneath the wall in the streamwise and spanwise directions. From the measured pressure field, the size of large-scale vortex was obtained. As a detailed study, a conditionally-averaging technique was employed to characterize the coherent structure of the large-scale vortex. To see the relationship between the flow field and the relevant spatial mode of the pressure field, the spatial box filtering (SBF) was examined. A cross-correlation between velocity and pressure fluctuations was performed to identify the structure and the length scale of the large-scale vortex.x.

Heat transfer coefficient measurement by a jet impinging on a rib-roughened convex surface (표면조도를 가지는 볼록한 면에 충돌하는 제트에 의한 열전달계수 측정)

  • Jeong, Yeong-Seok;Lee, Dae-Hui;Lee, Jun-Sik
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.22 no.3
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    • pp.373-385
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    • 1998
  • The local Nusselt numbers have been measured for a round turbulent jet impinging on the convex surface with and without rib. Liquid crystal/transient method was used to determine the Nusselt number distributions along the surface. The temperature on the surface was measured to within .+-.0.25 deg. C accuracy using liquid crystal and a digital color image processing system. The experiments were made for the jet Reynolds number (Re) 23,000, the dimensionless nozzle-to-surface distance (L/d) from 6 to 10, the dimensionless surface curvature (d/D) 0.056, and the various rib types (height(d$_{1}$) from 1 to 2 mm, pitch (p) from 6 to 32 mm). It was found that the average Nusselt numbers on the convex surface with rib are higher than those without rib, mainly due to an increase in the turbulent intensity caused by flow separation, recirculation and reattachment on the wall surface. In addition, we compared the results by the steady-state method using the gold-film Intrex with those by the transient method.

Numerical Analysis of the Unsteady Pressure fluctuation Generated from the Interaction between a Vortex Flow with a Forward Step (와류와 전향계단의 상호작용에 의한 비정상 벽면압력 변동의 수치해석)

  • 유기완;이준신
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.12 no.3
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    • pp.213-220
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    • 2002
  • Modifying effects of the rectangular forward step for suppressing the unsteady pressure fluctuation during interaction between the upstream vortical flow and the edge are studied numerically. The vertical flow is modeled by a point vortex, and the unsteady pressure coefficient is obtained from the velocity and the potential fields. To investigate the effects of the edge shape the rectangular forward step is chamfered wish various angles. Calculation shows that the pressure peaks become decreased by increasing the vortex height as well as the chamfering angle. The pressure amplitudes are very sensitive to the change of the initial vertex height and its strength. From this study we can find out that the chamfered edge has two effects; the one is that it suppresses the pressure amplitude generated from the edge, and the other is that it decreases the time variation of unsteady pressure fluctuation. These modifying concepts can be applied to attenuate the self-sustained oscillation mechanism at the open cavity flow.

A Numerical Analysis of Thermal Discharge using $\kappa-\imath$ Turbulence Closure ($\kappa-\imath$ 난류모델을 이용한 온배수 수치해석)

  • 최흥식
    • Water for future
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    • v.29 no.2
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    • pp.199-207
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    • 1996
  • To evaluate the usage of $\kappa-\imath$ turbulence closure for the analysis of thermal discharge behavior, a two-dimensional depth-integrated numerical model is developed. The developed model is applied to a steady flow in an open channel with simle geometry and the numerical results agree well with existing experimental data. The adequate simulation of recirculation, reattachment, and excess temperature rise at downstream of the outlet in the channel attributes to the correct calculation of turbulent eddy viscosity and diffusivity by $\kappa-\imath$ turbulence model. For an accurate prediction of thermal discharge behavior, the introduction of buoyancy production term, the modification of source/sink, and the correct input of turbulence constants of the $\kappa-\imath$ turbulence model are required.

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Numerical Study on the Flow Characteristics according to the Ventilation Holes Shape of the Carbon Composite Brake Disk (탄소복합재 브레이크 디스크의 통풍구 형상에 따른 유동특성에 관한 해석적 연구)

  • Ko, Dongguk;Yoon, Suckju
    • Transactions of the Korean Society of Automotive Engineers
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    • v.23 no.2
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    • pp.191-198
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    • 2015
  • In this study, the flow characteristics at the ventilation holes was analyzed by using numerical method when carbon composite brake disk was rotated at a constant speed. In order to ensure the validity of the analysis results, grid dependency test was performed by considering the accuracy and appropriateness, and 4mm mesh size was selected for decrease of the maximum error rate 63.6%. As a result, the outside air flows in the clearance between the disk and shaft in case of B model. whereas, the outside air flows in the clearance or the outlet of the ventilation holes in case of A and C models. And also average static pressure at the outlet was changed depending on shape of the ventilation holes and rotational speed of the disk in case of A and C models. Besides, in the B model, intake air according to the clearance goes with side surface of ventilation hole, and so increased by mean velocity of 4.64m/s and mean pressure of 0.58pa in the ventilation hole outlet, in case of disk rotational speed of 146.21rad/s.

Relation of necessity of the first aid education and attitude about traumatic dental injuries in some military men (일부 군인들의 치아외상에 대한 태도와 응급처치 교육필요성과의 관련성)

  • Kim, Yun-Jeong;Kim, Seon-Young;Shin, Dong-Min
    • Journal of Korean society of Dental Hygiene
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    • v.13 no.1
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    • pp.122-128
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    • 2013
  • Objectives : The purpose of this study was to investigate the traumatic injuries by first aid education and mouth protector in some military men. Methods : Among 195 military men, a total of 164 military men filled out the self-administered questionnaire and the return rate was 84.1%. The data were evaluated statistically using chi-square analysis. Results : 81.5% of respondents agreed that first aid education is necessary and 48.2% of respondents agreed that mouth protector of is necessary. In managing tooth fracture, subluxation, and avulsion, the military men answered the necessity of the first aid education revealed 87.2%, 86.8%, and 91.5%, respectively. The questions in managing tooth fracture, subluxation showed that mouth protector is necessary 56.3%, 49.0% respectively. In managing tooth fracture with reattachment, the necessity of the first aid education showed 88.9%. Conclusions : In order to get the knowledge about emergency treatment of traumatic injuries in military men, it is necessary to develop the professional education program for the dental hygiene personnel.

Salvage of Failed Digital Replantation Using Necrotizing Phalangeal Bone and Flap Coverage (수지 재접합 실패시 허혈 상태의 수지골과 피판술을 이용한 구제술)

  • Kwon, Boo-Kyung;Chung, Duke-Whan;Lee, Jae-Hoon
    • Archives of Reconstructive Microsurgery
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    • v.16 no.2
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    • pp.86-92
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    • 2007
  • Failure of reattachment of finger is inevitable in replantation surgery and that failure rate is about 10 % are reported in many authors. Management of the failed finger replantation is challenge to microsurgeons. We report 7 cases of thumb reconstruction after failure of replantation. The reconstructive surgery composed with early debridement of soft tissue that are under gangrenous processing, extract the phalangeal bone without any soft tissues. Osteosynthesis of the extracted phalangeal bone with host phalangeal bone. The exposed bony portion covered with vascularized flaps such as reverse radial forearm pedicled flap, free radial forearm flap and neurovascular island finger flap. This procedure underwent within a week after vascular insufficiency developed. All of the flaps are survived, bone union achieved within 3 months. The function and external appearance of the reconstructed thumb were encouraging; pinch power was average 1.2 pounds. Early removal of necrotizing soft tissue followed by covering none vascular phalangeal bone which extracted from the dead phalanx with vascularized flap is one of the useful alterative solutions in failed replantation surgery in hand.

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