• Title/Summary/Keyword: Reattachment

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Accessory Navicular in Sports Players (스포츠 선수에서 발생한 주상골 부골)

  • Lee, Kyung-Tae;Young, Ki-Won;Kim, J-Young;Kim, Eung-Soo;Cha, Seung-Do;Son, Sang-Woo
    • Journal of Korean Foot and Ankle Society
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    • v.8 no.2
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    • pp.161-165
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    • 2004
  • Purpose: To analyze clinical symptom and clinical course of accessory navicular bone and to evaluation of surgery of accessory navicular bone in sports players Materials and Methods: Twenty-two patients with accessory navicular bone were identified between January 1 2001 and June 30. 2003 Results: Subjective satisfaction of 23 patients rated very satisfaction (16), satisfaction (6), common (1). Symptomatic pain were thoroughly disappeared at average 2.5 months ($1{\sim}6$ months) after operation. On one year follow-up, most of patients could maintain daily life and could go back to their sports carreer at 3 months. Conclusion: In athlete, excision of accessory navicular and reattachment of posteior tibial tendon to navicular like non-athletes is the best solution to management of symptomatic accessory navicular failed to manage conservatively.

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Effect of Rib Height on Turbulence and Convective Heat Transfer (리브의 높이가 난류 및 열전달특성에 미치는 영향)

  • Nine, Md.J.;Kim, S.J.;Jeong, H.M.;Chung, H.S.;Rahman, M.Sq.
    • Journal of Power System Engineering
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    • v.16 no.6
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    • pp.30-37
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    • 2012
  • Effect of rib heights is found as significant parameter to enhance convective heat transfer performance under laminar and low turbulent regime. Circular ribs with different ribheight to channel height ratios, e/H = 0.05, 0.1, 0.15, are fabricated over the copper substrate respectively in a rectangular duct having 7.5 cross sectional aspect ratio. Only one rib pitch to rib height ratio (P/e = 10) has been chosen for all different height ribs. The result shows that the arithmetic average of turbulence intensity decreases with decreasing roughness height calculated between two ribs under laminar and low turbulent region. It occurs because the area of recirculation and reattachment zone also decreases with decreasing rib height. Optimum thermal enhancement factor is derived by 0.1 rib height to channel height ratio under low turbulent region but 0.15 rib height to channel height ratio gives maximum subjected to laminar flow.

Numerical Study for 3D Turbulent Flow in High Incidence Compressor Cascade (고입사각 압축기 익렬내의 3차원 난류유동에 관한 수치적 연구)

  • 안병진;정기호;김귀순;임진식;김유일
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2002.04a
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    • pp.35-40
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    • 2002
  • A numerical analysis based on two-dimensional and three-dimensional incompressible Navier-Stokes equations has been carried out for double-circular-arc compressor cascades and the results are compared with available experimental data at various incidence angles. The 2-D and 3-D computational codes based on SIMPLE algorithm adopt pressure weighted interpolation method for non-staggered grid and hybrid scheme for the convertive terms. Turbulence modeling is very important for prediction of cascade flows, which are extremely complex with separation and reattachment by adverse pressure gradient. In this paper k-$\varepsilon$ turbulence model with wall function is used to increase efficiency of computation times.

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Fluidic Characteristics of Precessing Jet Nozzle Combustor (세차제트노즐 연소기의 유동특성)

  • Lee, Hye-Young;Huh, Hwan-Il
    • Journal of the Korean Society of Propulsion Engineers
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    • v.11 no.4
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    • pp.1-9
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    • 2007
  • Many processing companies are facing environmental regulations such as decreasing NOx emissions when they by to increase thermal efficiencies of combustor. We study a potential new method that may achieve both increase of thermal efficiency and decrease of NOx emissions. This new concept of burner, the precessing jet burner, is known to significantly reduce pollutants such as NOx emissions and simultaneously increase radial heat transfer. This precessing jet nozzle may increase the combustion efficiency of gas turbine engine. A basic research on characteristics of precessing jet nozzle has been conducted using FLUENT and laser visualization technique. Velocities at He nozzle cross-section are compared with the published experimental results. Precessing jet nozzle with centerbody results in better precessing phenomena.

Effects of Duct Aspect Ratio on Heat Transfer in Wavy Duct of Heat Exchanger of Gas Turbine (가스터빈용 열교환기의 주름진 덕트에서 종횡비 변화가 열전달 특성에 미치는 영향)

  • Kim, Han Ho;Hwang, Sang Dong;Cho, Hyung Hee;Cho, Jae Ho;Jeon, Seung Bae
    • 유체기계공업학회:학술대회논문집
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    • 2001.11a
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    • pp.339-344
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    • 2001
  • The present study investigates convective heat/mass transfer and flow characteristics in wavy ducts of primary surface heat exchanger. Experiments using a naphthalene technique are carried out to determine the local transfer characteristics for flow in the corrugated wall duct. The aspect ratios of the rectangular duct cross-section are 7.3, 4.7 and 1.8 with a corrugation angle of $145^{\circ}$. The Reynolds numbers, based on the duct hydraulic diameter, are ranged from 1000 to 5000. The local heat/mass transfer measurement is conducted in the spanwise directions. The results show that Tayler-Gortler vortices exist on the pressure surface. Flow separation on the suction surface appears at a high Reynolds number resulting in a sharp decrease in the local transfer rates, but relatively high transfer rates are obtained in the reattachment region.

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Mechanism of Drag Reduction by Dimples and Roughness on a Sphere (구에 설치한 딤플과 표면 거칠기에 의한 항력 감소 메커니즘)

  • Choi, Jin;Jeon, Woo-Pyung;Choi, Hae-Cheon
    • 유체기계공업학회:학술대회논문집
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    • 2006.08a
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    • pp.191-194
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    • 2006
  • In this paper, we present a detailed mechanism of drag reduction by dimples and roughness on a sphere by measuring the streamwise velocity above the dimpled and roughened surfaces, respectively. Dimples cause local flow separation and trigger the shear layer instability along the separating shear layer, resulting in generation of large turbulence intensity. With this increased turbulence, the flow reattaches to the sphere surface with high momentum near the wall and overcomes strong adverse pressure gradient formed in the rear sphere surface. As a result, dimples delay main separation and reduce drag significantly. The present study suggests that generation of a separation bubble, i.e. a closed-loop streamline consisting of separation and reattachment, on a body surface is an important flow-control strategy for drag reduction on a bluff body such as the sphere and cylinder. In the case of roughened sphere, the boundary layer flow is directly triggered by roughness and changes to a turbulent flow. Due to this change, the drag significantly decreases. As the Reynolds number further increases, transition to turbulence occurs earlier on the sphere surface. Because of faster growth of turbulent boundary layer by roughness, earlier transition thickens the boundary layer, resulting in earlier separation and drag increase with increasing Reynolds number

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Augmented heat transfer in a rectangular duct with angled ribs (사각 덕트내 요철의 각도 변화에 따른 열전달 특성)

  • U, Seong-Je;Kim, Wan-Sik;Jo, Hyeong-Hui
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.22 no.4
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    • pp.530-541
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    • 1998
  • Heat transfer augmentation in a rib-roughened duct is affected by the rib configurations, such as rib height, angle of attack, shape, rib to rib pitch, and aspect ratio of a duct. These have been the main subjects in studying the average heat transfer and the friction loss of the fully developed flow. Investigating distributions of local heat transfer coefficients and flow patterns in a duct with the rib turbulators is necessary to find the characteristics of heat transfer augmentation and to decide the optimal configurations of ribs. In the present study the numerical analyses and the mass transfer experiments are performed to understand the flow through a rib roughened duct and the heat transfer characteristics with various angles of attack of ribs. A pair of counter-rotating secondary flow in a duct has a main effect on the lateral distributions of local mass transfer coefficients. Downwash of the rotating secondary flow, reattachment of main flow between ribs and the vortices near ribs and wall enhanced the mass transfer locally up to 8 times of that in case of the duct without ribs.

Convective heat transfer characteristics of a two-dimensional turbulent wall attaching offset jet (2차원 난류 벽부착제트의 대류열전달 특성)

  • Yun, Sun-Hyeon;Lee, Dae-Hui;Song, Heung-Bok;Kim, Dae-Seong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.10
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    • pp.3304-3312
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    • 1996
  • An experimental study on the convective heat transfer characteristics was performed for a two-dimensional wall attaching offset jet(WAOJ). Thermochromic liquid crystal was used to measure the plate wall temperature. The Nusselt number was measured for Reynolds numbers from 6, 500 to 39, 000, and the offset ratios from 0.5 to 15. The maximum Nusselt number point coincides with the time-averaged reattachment point and Nusselt number decreases monotonically after the jet reattaches on the wall. In the recirculation region Nusselt number minimize near the upstream corner and then increases as X/D decreases to vanishes. This suggests the existence of secondary vortices, causing an additional mixing of the flow in the corner. The correlations between the local Nusselt number and Reynolds number, Re, offset ratio, H/D, and streamwise distance, X/D are presented.

Heat Transfer Measurements by a Round Impinging Jet on a Rib-Roughened Flat Plate (표면조도를 가진 평판에서 원형충돌제트에 의한 열전달 측정)

  • Lee, Dae-Hee;Kim, Yun-Taek;Chung, Seung-Hun;Chung, Young-Suk
    • Proceedings of the KSME Conference
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    • 2000.11b
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    • pp.87-92
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    • 2000
  • This study is to investigate the heat transfer characteristics the for a round turbulent jet impinging on the flat plate 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 using liquid crystal and a digital color image processing system. The experiments were made fur the jet Reynolds number (Re) 23,000, the dimensionless nozzle-to-surface distance (L/d) from 2 to 10, and the rib type [height ($d_1$) 2mm, pitch (p) from 12 to 36mm]. It was found that for $L/d{\ge}6$ the average Nusselt numbers on the flat plate with rib type C ($p/d_1=16$) 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.

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NUMERICAL ANALYSIS OF THREE DIMENSIONAL SUPERSONIC CAVITY FLOW FOR THE VARIATION OF CAVITY SPANWISE RATIO (3차원 공동의 폭변화에 따른 초음속 유동에 대한 수치분석연구)

  • Woo, C.H.;Kim, J.S.;Choi, H.I.
    • 한국전산유체공학회:학술대회논문집
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    • 2006.10a
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    • pp.181-184
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    • 2006
  • High-speed flight vehicle have various cavities. The supersonic cavity flow is complicated due to vortices, flow separation and reattachment, shock and expansion waves. The general cavity flow phenomena include the formation and dissipation of vortices, which induce oscillation and noise. The oscillation and noise greatly affect flow control, chemical reaction, and heat transfer processes. The supersonic cavity' flow with high Reynolds number is characterized by the pressure oscillation due to turbulent shear layer, cavity geometry, and resonance phenomenon based on external flow conditions, The resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. In the present study, we performed numerical analysis of cavities by applying the unsteady, compressible three dimensional Reynolds-Averaged Navier-Stokes(RANS) equations with the ${\kappa}-{\omega}$ turbulence model. The cavity model used for numerical calculation had a depth(D) of 15mm cavity aspect ratio(L/D) of 3, width to spanwise ratio(W/D) of 1.0 to 5.0. Based on the PSD(Power Spectral Density) and CSD(Cross Spectral Density) analysis of the pressure variation, the dominant frequency was analyized and compared with the results of Rossiter's Eq.

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