• International Journal of Aeronautical and Space Sciences
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• 제18권1호
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• pp.70-81
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• 2017

Various components of an engine nozzle are modeled as flexible multi-body components that are operated under high temperature and pressure. In this paper, in order to predict complex behavior of an engine nozzle, thermo-fluid-flexible multi-body dynamics coupled analysis framework was developed. Temperature and pressure on the nozzle wall were obtained by the steady-state flow analysis for a two-dimensional nozzle. The pressure and temperature-dependent material properties were delivered to the flexible multi-body dynamics analysis. Then the deflection and strain distribution for a nozzle configuration was obtained. Heat conduction and thermal analyses were done using MSC.NASTRAN. The present framework was validated for a simple nozzle configuration by using a one-way coupled analysis. A two-way coupled analysis was also performed for the simple nozzle with an arbitrary joint clearance, and an asymmetric flow was observed. Finally, the total strain result for a realistic nozzle configuration was obtained using the one-way and two-way coupled analyses.

• Wind and Structures
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• 제12권6호
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• pp.541-551
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• 2009

This paper explains how to correctly measure the drag coefficient of a circular cylinder in wind tunnels with large blockage ratios and for the sub-critical to the super-critical flow regimes. When dealing with large blockage ratios, the drag has to be corrected for wall constraints. Different formulations for correcting blockage effect are compared for each flow regime based on drag measurements of smooth circular cylinders performed in a wind tunnel for three different blockage ratios. None of the correction model known in the literature is valid for all the flow regimes. To optimize the correction and reduce the scatter of the results, different correction models should be combined depending on the flow regime. In the sub-critical regime, the best results are obtained using Allen and Vincenti's formula or Maskell's theory with ${\varepsilon}$=0.96. In the super-critical regime, one should prefer using Glauert's formula with G=0.6 or the model of Modi and El-Sherbiny. The change in the formulations appears at the flow transition with a variation of the wake pattern when passing from sub-critical to super-critical flow regimes. This parameter being not considered in the known blockage corrections, these theories are not valid for all the flow regimes.

• 수산해양기술연구
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• 제56권4호
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• pp.395-406
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• 2020

The objectives of this study were to develop the optimal structures of recirculating aquaculture tank for improving the removal efficiency of solid materials and maintaining water quality conditions. Flow analysis was performed using the CFD (computational fluid dynamics) method to understand the hydrodynamic characteristics of the circular tank according to the angle of inclination in the tank bottom (0°, 1.5° and 3°), circulating water inflow method (underwater, horizontal nozzle, vertical nozzle and combination nozzle) and the number of inlets. As the angle in tank bottom increased, the vortex inside the tank decreased, resulting in a constant flow. In the case of the vertical nozzle type, the eddy flow in the tank was greatly improved. The vertical nozzle type showed excellent flow such as constant flow velocity distribution and uniform streamline. The combination nozzle type also showed an internal spiral flow, but the vortex reduction effect was less than the vertical nozzle type. As the number of inlets in the tank increased, problems such as speed reduction were compensated, resulting in uniform fluid flow.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.501-517
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• 2020

Three-dimensional numerical simulations were performed to study the effects of flow direction and flow velocity on the flow regime behind a curved pipe represented by a curved circular cylinder. The cylinder is based on a previous study and consists of a quarter segment of a ring and a horizontal part at the end of the ring. The cylinder was rotated in the computational domain to examine five incident flow angles of 0-180° with 45° intervals at Reynolds numbers of 100 and 500. The detailed wake topologies represented by λ2 criterion were captured using a Large Eddy Simulation (LES). The curved cylinder leads to different flow regimes along the span, which shows the three-dimensionality of the wake field. At a Reynolds number of 100, the shedding was suppressed after flow angle of 135°, and oblique flow was observed at 90°. At a Reynolds number of 500, vortex dislocation was detected at 90° and 135°. These observations are in good agreement with the three-dimensionality of the wake field that arose due to the curved shape.

• 한국가스학회지
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• 제20권4호
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• pp.65-77
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• 2016

Fischer-Tropsch 반응기 내 복잡한 반응과 흐름을 상세히 모델링하는 것은 CFD 분야에 있어 도전적 과제이다. Fischer-Tropsch 반응은 여러 가지 탄소수를 가진 탄화수소들을 만들어내는데, 탄화수소에는 무수히 많은 이성질체가 존재하는 이유로 모든 화학종에 대해서 각각의 반응속도식을 도출해 적용하는 것은 어렵다. 이의 극복을 위해 기존 연구들에서 사용된 반응속도식 모델링 방법론들을 분석한 뒤, 화학종별 상세한 반응속도식 적용을 위해 non-Anderson-Schulz-Flory 방법론을 선정하여 상세 모델링을 진행하였다. 또한 반응 특성상 다상 흐름 형태를 띠는데, 다상 흐름 모델링의 경우 상간의 간섭이나 분산상의 분포 및 유동 형태 등에 따라 적합한 모델링 방법론이 다르다. 그러나 기존 연구들에서는 타당성에 대한 논의나 근거 제시 없이 각양각색의 내부 흐름 모델링 방법론이 사용되고 있다. 실험을 통해 내부 흐름 형태를 관찰한 뒤 유동 형태에 따른 모델링을 진행하는 것이 최선이나, 자원 여건상 어려움이 있어, 본 연구에서는 전통적인 유체역학 이론에 근거해 내부 흐름 형태를 먼저 추론하고 Mixture 모델 방법론을 선정하여 체계적인 CFD 모델링을 진행함으로써, 사용된 방법론에 대한 근거를 마련하고자 하였다. 10가지 실험조건에서 진행한 실험 결과와 본 연구의 시뮬레이션 결과를 비교하였으며, 이를 통해 본 연구가 제안하는 체계적 모델링 방법론의 타당성을 입증하였다.

• 한국산학기술학회논문지
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• 제20권12호
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• pp.519-524
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• 2019

본 연구에서는 대풍량 곡물건조기에 사용되는 수평형 집진기의 집진효율 향상과 최적화를 위한 연구의 선행과정으로 Computational Fluid Dynamics(CFD)를 이용하여 집진기 내부의 유동 특성 분석과 원뿔형 허브의 각 변화가 집진기의 집진성능에 미치는 영향을 해석하였다. 최근 집진기 입구에 원뿔형 허브와 고정 베인을 설치하여 선회유동(Swirl Flow)을 발생시켜 이물질을 공기와 분리시키는 수평형 사이클론 집진기(Horizontal type Cyclone Dust collector)가 개발되었다. 이 집진기는 크기가 비교적 작고 설치가 용이하고 비교적 배압이 낮아 추가 동력을 필요로 하지 않으며 베인의 선회력을 이용하기 때문에 대풍량 배습용 송풍기에도 적용할 수 있는 장점을 가지고 있다. 그러나 수평형 집진기 형상으로 인해 발생하는 집진기 내부의 배압 문제와 분진 퇴적 문제를 해결하기 위해서 3차원 유동해석을 이용하여 집진기 내부 형상 변화에 따른 유동 특성에 관한 연구를 진행하였다. 실제 곡물건조기에 적용 가능한 수평형 집진기 설계를 위한 기초 자료를 제공하였으며, 향후 연구 예정인 고정 베인 설계, 주분리관 및 중간분리관의 설계에 적용하고자 한다.

• 한국공작기계학회논문집
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• 제11권6호
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• pp.75-82
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• 2002

Design for a quiet operation of fluid power system requires the understanding of noise and vibration characteristics of the system. It's not easy to analyze noise problem in hydraulic cylinder used in typical actuator Because they've got complex fluid dynamics. One of the fundamental problems associated with the hydraulic system is the pulsating flow in pipe lines, which can be tackled by the analysis under simplifying assumptions. The present study focuses on theoretic analysis and experimental study on the dynamics of laminar pulsating flow in a circular pipe. We analyze the propagation characteristics of the pressure pulse within a hydraulic pipe line taking into account the pulsating flow frequency variation. We also measure instantaneous pressure pulses within pipe line to identify the transfer functions. We conduct series of experiments to investigate the propagation characteristics of pressure pulse for various pressure of pulsating flow. The working fluid of the present study is ISO VG46 and the temperature ranges from 20 to $60^{\circ}$ with normal pressure at 4000kPa. The flow rate is measured by using an ultrasonic flow meter. Pressures at fixed upstream and downstream positions are measured concurrently. The electric signals of the pressure sensor are stored and analyzed using a system analyzer(PKE 983 series). The frequency is varied in the range of 10~500Hz. The Reynolds number is kept below 2,000. In the present study, boundary condition was varied by installing a surge tank and an orifice at the end of pipe. Experimental and theoretical results were compared each other under various boundary conditions.

• Journal of Korean Neurosurgical Society
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• 제61권6호
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• pp.689-699
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• 2018

Objective : The goal of this study was to compare several parameters, including wall shear stress (WSS) and flow pattern, between unruptured and ruptured anterior communicating artery (ACoA) aneurysms using patient-specific aneurysm geometry. Methods : In total, 18 unruptured and 24 ruptured aneurysms were analyzed using computational fluid dynamics (CFD) models. Minimal, average, and maximal wall shear stress were calculated based on CFD simulations. Aneurysm height, ostium diameter, aspect ratio, and area of aneurysm were measured. Aneurysms were classified according to flow complexity (simple or complex) and inflow jet (concentrated or diffused). Statistical analyses were performed to ascertain differences between the aneurysm groups. Results : Average wall shear stress of the ruptured group was greater than that of the unruptured group (9.42% for aneurysm and 10.38% for ostium). The average area of ruptured aneurysms was 31.22% larger than unruptured aneurysms. Simple flow was observed in 14 of 18 (78%) unruptured aneurysms, while all ruptured aneurysms had complex flow (p<0.001). Ruptured aneurysms were more likely to have a concentrated inflow jet (63%), while unruptured aneurysms predominantly had a diffused inflow jet (83%, p=0.004). Conclusion : Ruptured aneurysms tended to have a larger geometric size and greater WSS compared to unruptured aneurysms, but the difference was not statistically significant. Flow complexity and inflow jet were significantly different between unruptured and ruptured ACoA aneurysms.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 춘계학술대회논문집
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• pp.159-164
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• 2009

The water droplet motion and the interaction between the droplets in a PEMFC air flow channel with multiple pores, through which water emerges, is studied numerically by solving the equations governing the conservation of mass and momentum. The liquid-gas interface is tracked by a level set method which is based on a sharp-interface representation for accurately imposing the matching conditions at the interface. The method is modified to implement the contact angle conditions on the walls and pores. The dynamic interaction between the droplets growing on multiple pores while keeping the total water flow rate through pores constant is investigated by conducting the computations until the droplet motion exhibits a periodic pattern. The numerical results show that the droplet merging caused by increasing the number of pores is not effective for water removal and that the contact angle of channel wall strongly affects water management in the PEMFC air flow channel.

• 한국가시화정보학회지
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• 제8권3호
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• pp.49-55
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• 2010

Thermal flows inside a laser printer are affected by generated heat from a fuser and boards. Thus, the effect of fans has been investigated to control the thermal flows and behaviors of toners. In order to analyze the phenomena experimentally, a PIV (Particle Image Velocimetry) has been used, and then the flow inside the printer has been predicted by the CFD (Computational Fluid Dynamics) in this study to determine the efficient flow distribution by an optimum design of the printer. The determined optimum design has been confirmed by the developed PIV technique so that the efficiency of the laser printer can be improved by the proposed design.