• Title/Summary/Keyword: Annular flow

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Added Mass, Viscous Damping and Fluid-stiffness Coefficients on the Rotating Inner Cylinder in Concentric Annulus (동심환내의 회전체 진동에 의한 부가질량, 유체감쇠계수 및 유체탄성계수에 관한 연구)

  • 심우건;박진호;김기선
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2001.05a
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    • pp.695-701
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    • 2001
  • While a rotating inner cylinder executes a periodic translational motion in concentric annulus, the vibration of the rotating inner cylinder is induced by fluid-dynamic forces acting on the cylinder. In the previous study related to journal bearing, the unsteady viscous flow in the annulus and the fluid-dynamic forces were evaluated based on a numerical approach. Considering the dynamic-characteristics of unsteady viscous flow, an approximate analytical method has been developed for estimating added mass, viscous damping and fluid-stiffness coefficients. For the study of flow-induced vibrations and related instabilities, it is of interest to separate the coefficients from the fluid-dynamic forces. The added-mass and viscous damping coefficients for very narrow annular configurations, as journal bearing. can be approximated by considering the gap ratio to the radius of inner cylinder, while the fluid-stiffness coefficient is related to the Reynolds number, the oscillatory Reynolds number and the gap ratio.

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Propulsive Performance Analysis of Ducted Marine Propulsors with Rotor-Stator Interaction

  • Jang, Jin-Ho;Yu, Hye-Ran;Jung, Young-Rae;Park, Warn-Gyu
    • Journal of Ship and Ocean Technology
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    • v.8 no.1
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    • pp.31-41
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    • 2004
  • A ducted marine propulsor has been widely used for the thruster of underwater vehicles for protecting collision damage, increasing propulsive efficiency, and reducing cavitation. Since a single-stage ducted propulsor contains a set of rotor and stator inside an annular duct, the numerical analysis becomes extremely complex and computationally expensive. However, the accurate prediction of viscous flow past a ducted marine propulsor is essential for determining hydrodynamic forces and the propulsive performances. To analyze a ducted propulsor having rotor-stator Interaction, the present work has solved 3D incompressible RANS equations on the sliding multiblocked grid. The flow of a single stage turbine flow was simulated for code validation and time averaged pressure coefficients were compared with experiments. Good agreement was obtained. The hydrodynamic performance coefficients were also computed.

DEVELOPMENT OF AN LES METHODOLOGY FOR COMPLEX GEOMETRIES

  • Merzari, Elia;Ninokata, Hisashi
    • Nuclear Engineering and Technology
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    • v.41 no.7
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    • pp.893-906
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    • 2009
  • The present work presents the development of a Large Eddy Simulation (LES) methodology viable for complex geometries and suitable for the simulation of rod-bundles. The use of LES and Direct Numerical Simulation (DNS) allows for a deeper analysis of the flow field and the use of stochastical tools in order to obtain additional insight into rod-bundle hydrodynamics. Moreover, traditional steady-state CFD simulations fail to accurately predict distributions of velocity and temperature in rod-bundles when the pitch (P) to diameter (D) ratio P/D is smaller than 1.1 for triangular lattices of cylindrical pins. This deficiency is considered to be due to the failure to predict large-scale coherent structures in the region of the gap. The main features of the code include multi-block capability and the use of the fractional step algorithm. As a Sub-Grid-Scale (SGS) model, a Dynamic Smagorinsky model has been used. The code has been tested on plane channel flow and the flow in annular ducts. The results are in excellent agreement with experiments and previous calculations.

Study on Static Characteristics of Hybrid Spool Valve (하이브리드 스폴밸브의 정특성 연구)

  • Yun, So-Nam;Ham, Young-Bok;Kim, Dong-Su
    • Proceedings of the KSME Conference
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    • 2001.06b
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    • pp.121-126
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    • 2001
  • In this study, the 4-way spool valve characteristics are clearly defined and proposed new type of spool valve. This paper presents governing equations of the flow through clearances between sleeve and spool as a model of orifice flow for null characteristic analysis, and programmed analysis software of it. This software is possible to basically analysis that not only which case of open center, closed center or critical center but +,- displacement of spool, lab position, boundary region and spool opening of the valve, and to estimate the pressure variation in the spool and external leak flow variation. We are convinced that the scale of load pressure difference is changed as lab condition of spool valve, and this scale is changed with boundary point on the annular clearance. It is vary useful to designer and user of spool valve with this design data and analysis software.

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Prediction of Combination-Type-Staggered-Labyrinth Seal Leakage Using CFD (CFD를 사용한 복잡한 형상을 갖는 래버린스 실의 누설량 예측)

  • Ha Tae-Woong
    • Tribology and Lubricants
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    • v.22 no.2
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    • pp.66-72
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    • 2006
  • Leakage reduction through annular type labyrinth seals of steam turbine is necessary for enhancing their efficiency and the precise prediction method of seal leakage is needed. In this study, numerical analysis for leakage prediction of the combination-type-staggered-labyrinth seal has been carried out using FLUENT 6 which is commercial CFD (Computational Fluid Dynamics) code based on FVM (Finite Volume Method) and SIMPLE algorism. The present CFD results are verified with the theoretical analysis based on Bulk-flow concept which has been mainly used in predicting seal leakage. Comparing with the result of Bulk-flow model analysis, the leakage result of CFD analysis shows good agreement within 7.1% error.

Flow Characteristics of Annular Gas Turbine Combustor (환형 가스터빈엔진 연소기 유동 특성 연구)

  • Woo S. P.;Jeung I. S.
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2004.10a
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    • pp.36-40
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    • 2004
  • Experimental and numerical studies are carried out for inner flow of small gas turbine engine combustor at normal operating altitude and velocity. First of all inner flow and combustion phenomenon without a load is analyzed for understanding with various back pressure condition due to flight mode of smart UAV.

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An Experimental Study on Heat Transfer Characteristics Just Before Critical Heat Flux in Uniformly Heated Vertical Annulus Under a Wide Range of Pressures

  • Chun, Se-Young;Moon, Sang-Ki;Chung, Heung-June;Chung, Moon-Ki
    • Nuclear Engineering and Technology
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    • v.34 no.4
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    • pp.269-285
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    • 2002
  • Water heat transfer experiments were carried out in a uniformly heated annulus with a wide range of pressure conditions. The local heat transfer coefficients for saturated water (low boiling have been measured just before the occurrence of the critical heat flux (CHF) along the length of the heated section. The trends of the measured heat transfer coefficients were quite different from the conventional understanding for the heat transfer of saturated flow boiling. This discrepancy was explained from the nucleate boiling in the liquid film of annular flow under high heat flux conditions. The well-known correlations were compared with the measured heat transfer coefficients. The Shah and Kandlikar correlations gave better prediction than the Chen correlation. However, the modified Chen correlation proposed in the present work showed the best agreement with the present data among correlations examined .

Study on Pressure drop characteristics in HTS cable core with two flow passages

  • Lee, Jun-Kyoung;Kim, Seok-Ho;Kim, Hae-Joon;Cho, Jeon-Wook
    • Progress in Superconductivity and Cryogenics
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    • v.10 no.4
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    • pp.33-37
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    • 2008
  • The main objective of this study is to identify the pressure drop characteristics of coolant flow passages of 154kV/1GVA High Temperature Superconducting (HTS) power cable, experimentally. The passages were consisted of two parts, the one is the circular path with spiral ribs in the core to cool the cable conductor layer and the other is annular path with spirally corrugated outer wall to cool the shield layer. Thus the experiments to acquire the pressure drop data were performed with two types of circular spiral tubes and eight types of the concentric annuli in various range of Reynolds number. The pressure drops in the core tubes and the annuli were much higher than those in the tubes with smooth surface. Therefore, modified correlations to present the experimental results in each flow passage were suggested.

Dissipation and Control of Flow Instability in a Rectangular Swirl Combustor using Cooling Flow Injection (사각 스월 연소기에서 냉각 유동을 이용한 연소기 내 유동 불안정 감쇠 및 조종)

  • Yoo, Kwang-Hee;Kim, Jong-Chan;Sung, Hong-Gye
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2009.11a
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    • pp.236-241
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    • 2009
  • To identify turbulent flow characteristics of non-reacting case resulted from cooling flow injection in a rectangular swirl combustor, 3D Large Eddy Simulation(LES) was implemented and Proper Orthogonal Decomposition(POD) analysis was used for post-processing. The combustor of concern is the LM6000, lean premixed dry low-NOx annular combustor, developed by GEAE. It was observed that increase in speed of shear layer resulted from the inflow of cooling flow caused intensified vorticity magnitude in central toroidal recirculation zone. In the case of vorticity magnitude in corner recirculation zone, however, was weakened. In addition, pressure fluctuation in combustor was damped down and longitudinal acoustic mode was significantly dissipated

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1-D Two-phase Flow Investigation for External Reactor Vessel Cooling (원자로 용기 외벽냉각을 위한 1차원 이상유동 실험 및 해석)

  • Kim, Jae-Cheol;Park, Rae-Joon;Cho, Young-Rho;Kim, Sang-Baik;Kim, Sin;Ha, Kwang-Soon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.5
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    • pp.482-490
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    • 2007
  • When a molten corium is relocated in a lower head of a reactor vessel, the ERVC (External Reactor Vessel Cooling) system is actuated as coolant is supplied into a reactor cavity to remove a decay heat from the molten corium during a severe accident. To achieve this severe accident mitigation strategy, the two-phase natural circulation flow in the annular gap between the external reactor vessel and the insulation should be formed sufficiently by designing the coolant inlet/outlet area and gap size adequately on the insulation device. For this reason, one-dimensional natural circulation flow tests and the simple analysis were conducted to estimate the natural circulation flow under the ERVC condition of APR1400. The experimental facility is one-dimensional and scaled down as the half height and 1/238 channel area of the APR1400 reactor vessel. The calculated circulation flow rate was similar to experimental ones within about ${\pm}$15% error bounds and depended on the form loss due to the inlet/outlet area.