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  • Title/Summary/Keyword: CFD 유동해석

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A Computational Study of the Focusing Phenomenon of Weak Shock Wave (약한 충격파의 포커싱 현상에 관한 수치해석적 연구)

  • Kweon Yong Hun;Kim Heuy Dong
    • Proceedings of the KSME Conference
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    • 2002.08a
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    • pp.169-172
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    • 2002
  • When a plane shockwave reflects ken a concave wall, it is focused at a certain location, resulting in extremely high local pressure and temperature. This focusing is due to a nonlinear phenomenon of shock wave. The focusing phenomenon has been extensively applied to many diverse folds of engineering and medical treatment as well. In the current study, the focusing of shock wave over a reflector is numerically investigated using a CFD method. The Harten-Yee total variation diminishing (TVD) scheme is used to solve the unsteady, two-dimensional, compressible, Euler equations. The incident shock wave Mach number Msof1.1\~l.3 is applied to the parabolic reflectors with several different depths. Detailed focusing characteristics of the shock wave are investigated in terms of peak pressure, gasdynamic and geometrical foci. The results obtained are compared with the previous experimental results. The results obtained show that the peak pressure of shock wave focusing and its location strongly depend on the magnitude of the incident shock wave and depth of parabolic reflector. It is also found that depending up on the depth of parabolic reflector, the weak shock wave focusing process can classified into three distinct patterns : the reflected shock waves do not intersect each other before and after focusing, the reflected shock waves do not intersect each other before focusing, but intersect after focusing, and the reflected shock waves intersect each other before and after focusing. The predicted Schlieren images represent the measured shock wave focusing with a good accuracy.

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Influence of the Nozzle Contraction Angles of Gaseous Extinguishing Systems on Discharge Noise (가스계 소화시스템 노즐 수축각이 방출소음에 미치는 영향)

  • Kim, Yo-Hwan;Yoo, Han-Sol;Hwang, In-Ju;Kim, Youn-Jea
    • Fire Science and Engineering
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    • v.33 no.4
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    • pp.77-82
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    • 2019
  • Fire extinguishing systems are essential equipment in all indoor facilities to address unexpected fire scenarios, and appropriate fire extinguishing agent should be used depending on the place and object to protect. Among these, gaseous fire-extinguishing systems are used to protect electronic equipment. Therefore, inert gases that do not undergo chemical reactions are used mainly in those systems. On the other hand, recently, owing to the high integration of electronic equipment, there are some cases, in which large noise generated from gaseous systems damage the electronic equipment. In this study, numerical analysis of the discharge noise with various nozzle contraction angles was carried out to improve the gas fire extinguishing system. Numerical analysis was carried out using ANSYS FLUENT ver 18.1. The causes of the noise were elucidated using the swirl distribution. The noise level of the modified model was reduced by approximately 6 dB compared to the reference model, which is similar to the result of a previous study, confirming the validity of the method.

Parallelization of Multi-Block Flow Solver with Multi-Block/Multi-Partitioning Method (다중블록/다중영역분할 기법을 이용한 유동해석 코드 병렬화)

  • Ju, Wan-Don;Lee, Bo-Sung;Lee, Dong-Ho;Hong, Seung-Gyu
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.31 no.7
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    • pp.9-14
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    • 2003
  • In this work, a multi-block/multi-partitioning method is suggested for a multi-block parallelization. It has an advantage of uniform load balance via subdividing of each block on each processor. To make a comparison of parallel efficiency according to domain decomposition method, a multi-block/single-partitioning and a multi-block/ multi-partitioning methods are applied to the flow analysis solver. The multi-block/ multi-partitioning method has more satisfactory parallel efficiency because of optimized load balancing. Finally, it has applied to the CFDS code. As a result, the computing speed with sixteen processors is over twelve times faster than that of sequential solver.

Design of Sharp-edged Type Damping Orifices for an Aircraft Door Damper (민항기 door damper용 칼날형 댐핑 오리피스의 설계)

  • Hong, Yeh-Sun;Kwon, Yong-Cheol;Kim, Chong-Hyeok;Park, Seol-Hye;Park, Ho-Yeol;Kim, Sang-Beom
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.40 no.12
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    • pp.1080-1085
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    • 2012
  • In this paper a sharp-edged type damping orifice for an aircraft door damper were designed, where the dynamic viscosity of working fluid were assumed to change up to 400cSt. The discharge coefficient of the damping orifice were investigated by CFD analyses and experiments. In particular, the influences of orifice diameter, edge angle, flow direction and the Reynolds number were taken into consideration. Based on this, it has been deduced how high Coulomb friction forces of damper seals is to be allowed to meet the performance criterion with respect to the orifice size.

A Study on Numerical Analysis of Flow Uniformity According to Length and Degree Change of Mixed-Evaporator in 500 PS SCR Reactor (500 PS SCR 반응기 혼합증발관 길이와 각도 변화에 따른 유동균일도에 대한 수치해석적 연구)

  • Seong, Hongseok;Lee, Chungho;Suh, Jeongse
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.28 no.8
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    • pp.337-342
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    • 2016
  • A marine SCR System is emerging as an alternative to comply with NOx Tier III Emission standards, a restriction on greenhouse gas from vessels implemented by the International Maritime Organization. The system is greatly affected by the uniformity of the fluid flowing into the catalyst, so the performance of the catalyst of an SCR system needs to be guaranteed. This study conducted research on a mixed evaporator of an SCR system, which is one of the factors affecting the uniformity of the fluid. When the angle of the mixed evaporator is set to 90, the fluid uniformity is at its highest at 83%, under the condition that the length of the mixed evaporator be 3.5 D. When the length was 3.5 D and less, the fluid uniformity had a tendency to improve relative to the case without a bent pipe. However, a longer mixed evaporator results in a more perfect liquidity development in the pipe with a liquidity distribution similar to the case where no curved pipe is formed in front of the catalyst. A lower angle for the mixed evaporator results in a lower flow uniformity, and a longer length of the mixed evaporator results in a lower difference in the flow uniformity caused by the angle. The flow uniformity can be improved by 6% with a mixed evaporator, which confirmed that all factors applied to an SCR system have a close relationship with the efficiency.

Numerical Analysis of Supercavitating Flows of Two-Dimensional Simple Bodies (2차원 단순 물체의 초공동 유동에 대한 수치해석)

  • Lee, Hyun-Bae;Choi, Jung-Kyu;Kim, Hyoung-Tae
    • Journal of the Society of Naval Architects of Korea
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    • v.50 no.6
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    • pp.436-449
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    • 2013
  • In this paper, a numerical analysis is carried out to study the characteristics of supercavitating flows and the drag of relatively simple two-dimensional and axisymmetric bodies which can be used for supercavity generation device, cavitator, of a high-speed underwater vehicle. In order to investigate the suitability of numerical models, cavity flows around the hemispherical head form and two-dimensional wedge are calculated with combinations of three turbulence models(standard kϵ, realizable kϵ, Reynolds stress) and two cavitation models(Schnerr-Sauer, Zwart-Gerber-Belamri). From the results, it is confirmed that the calculated cavity flow is more affected by the turbulence model than the cavitation model. For the calculation of steady state cavity flows, the convergence in case of the realizable kϵ model is better than the other turbulence models. The numerical result of the Schnerr-Sauer cavitation model is changed less by turbulence model and more robust than the Zwart-Gerber-Belamri model. Thus the realizable kϵ turbulence model and the Schnerr-Sauer cavitation model are applied to calculate supercavitating flows around disks, two dimensional 10 and 30 wedges. In case of the disk, the cavitation number dependences of the cavity size and the drag coefficient predicted are similar to either experimental data or Reichardt's semi-empirical equations, but the drag coefficient is overestimated about 3% higher than the Reichardt's equation. In case of the wedges, the cavitation number dependences of the cavity size are similar to experimental data and Newman's linear theory, and the agreement of the cavity length predicted and Newman's linear theory becomes better as decreasing cavitation number. However, the drag coefficients of wedges agree more with experimental data than those of Newman's analytic solution. The cavitation number dependences of the drag coefficients of both the disk and the wedge appear linear and simple formula for estimating the drag of supercavitating disks and wedges are suggested. Consequently, the CFD scheme of this study can be applied for numerical analysis of supercavitating flows of the cavitator and the cavitator design.

Numerical Investigation of Flow Structures near Various Nozzle Exit Geometries of the Air Bearing (공기베어링의 노즐 형상 변화에 따른 출구면 근방의 유동구조에 대한 수치해석)

  • Park, Byung Ho;Han, Yong Oun;Park, Sang-Shin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.38 no.3
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    • pp.235-242
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    • 2014
  • To investigate pressure distributions on the shaft surface of the air bearing, the commercial CFD software was employed to study three different nozzle geometries to improve the nozzle performance: general drill-shaped, matched cube-shaped and trimmed exit nozzles. Under the influence of stagnation point, the maximum pressure was observed at the center of shaft surface for all cases. Owing to the blocking effect of a fine gap between the shaft surface and the nozzle exit, the drill-shaped nozzle has the rapid local pressure increase near the nozzle exit corner, generating the ring vortex in the radial direction within pressure ratio of 6.92, and its pressure becomes negative in a certain range of downstream. In comparison, the contoured nozzle showed a local pressure increase in the measured range of pressure ratios, but a negative pressure appeared within the pressure ratio of about 10. The trimmed nozzle was seemed to extend the high pressure zone near the stagnation point in the radial direction substantially, and no negative pressure was appeared in the whole range. Based on these observations, it is found that trimming nozzle exit becomes more effective for improving the performance than modifying the nozzle inside contour.

Optimal arrangement of multiple wind turbines on an offshore wind-wave floating platform for reducing wake effects and maximizing annual energy production (다수 풍력터빈의 후류영향 최소화 및 연간발전량 극대화를 위한 부유식 파력-해상풍력 플랫폼 최적배치)

  • Kim, Jong-Hwa;Jung, Ji-Hyun;Kim, Bum-Suk
    • Journal of Advanced Marine Engineering and Technology
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    • v.41 no.3
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    • pp.209-215
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    • 2017
  • A large floating offshore wind-wave hybrid power generation system with an area of 150 m2 and four 3 MW class wind turbine generators was installed at each column top. In accordance with the wind turbine arrangement, the wake generated from upstream turbines can adversely affect the power performance and load characteristics of downstream turbines. Therefore, an optimal arrangement design, obtained through a detailed flow analysis focusing on wake interference, is necessary. In this study, to determine the power characteristics and annual energy production (AEP) of individual wind turbines, transient computational fluid dynamics, considering wind velocity variation (8 m/s, 11.7 m/s, 19 m/s, and 25 m/s), was conducted under different platform conditions (0, 22.5, and 45). The AEP was calculated using a Rayleigh distribution, depending on the wind turbine arrangement. In addition, we suggested an optimal arrangement design to minimize wake losses, based on the AEP.

Characteristics of Heat Transfer and Chemical Reaction in Reformer Tube for Fuel Reynolds Number and Burner Gas Temperature (개질관 내부 레이놀즈 수와 버너 온도에 따른 열유동 및 반응 특성)

  • Han, Jun Hee;Yoon, Kee Bong;Kim, Ji Yoon;Lee, Seong Hyuk
    • Journal of the Korean Institute of Gas
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    • v.19 no.5
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    • pp.69-74
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    • 2015
  • The study investigated numerically the heat transfer and chemical reaction characteristics of a methane-steam reforming by using a 3-dimensional computational fluid dynamics (CFD) code (Fluent ver. 16.1). The fuel temperature and its species mole fractions were estimated for various Reynolds number in the reformer tube at different burner temperatures. The catalysts were modeled as the porous medium of nicrome in the reformer tube. We considered radiation effect as well as conduction and convective heat transfer because the methane-steam was reformed at very high temperature condition above 1000 K. For two different Reynolds numbers of 49,000 and 88,000 and the burner temperatures were in the range from 1,100 K to 1,300 K. At a low Reynolds number, the fuel temperature increased, leading to increase in hydrogen reforming. However, fuel temperature and hydrogen reforming decreased because of higher convective heat transfer from relatively low fuel temperature. Moreover, the hydrogen reforming also increased with burner temperature.

A Numerical Calculation for the Optimum Operation of Cyclone-based Combustion System (선회류 방식 연소시스템의 최적 조업을 위한 수치해석)

  • Kim, Min-Choul;Lee, Jae-Jeong;Lee, Gang-Woo;Kim, Ji-Won;Shon, Byung-Hyun
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.12 no.2
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    • pp.1005-1012
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    • 2011
  • This research carried out a 3-dimensional simulation using computerized fluid dynamics (CFD) for the flow characteristics, temperature distribution, velocity distribution and residence time, etc. in a reactor in order to derive the optimal combustion conditions of an innovative combustion system. The area-weighted average temperature of the outlet of a furnace during combustion at a condition of fuel input rate 1.5 ton/hr, residence time 1.25 sec and air/fuel ratio 2.1 was 1,077C, which is a suitable temperature for energy recovery and treatment of air pollutants. Exhaust gas is discharged through a duct at a 40~50 m/s maximum speed along strong vortexes at the center of a combustion chamber, so strong turbulence is created at the center of a combustion chamber to enhance the combustion speed and combustion efficiency. In this system, the optimum operation conditions to prevent incomplete combustion and suppress the formation of thermal NOx were air/fuel ratio 1.9~2.1 and fuel input rate 1.25~1.5 ton/hr.