• 한국추진공학회지
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• 제8권2호
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• pp.62-72
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• 2004

본 연구에서는 우선 전산 결과의 신뢰성을 검증하기 위하여 동일 조건의 실험결과와 비교하였다. 그 결과를 살펴보면 전산결과와 실험결과가 대체적으로 잘 일치하였다. 다음으로 압력면 및 흡입면의 원호반경, 피치 코드비등의 설계인자에 따른 유동해석을 실시하였다. 익렬내의 유동 및 성능 특성은 익렬 앞전 및 노즐 끝단에서 발생하는 충격파와 익렬 내부에서 발생하는 박리에 의해 주로 좌우되었다. 그리고 노즐 끝단에서 발생하는 충격파와 박리는 익렬 내부 유로 면적에 의해서 좌우되었으며, 익렬 앞전에서 발생하는 충격파는 노즐이 차지하고 있는 익렬 개수에 의해 영향을 받았다.

• 대한기계학회논문집B
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• 제27권1호
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• pp.84-94
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• 2003

It is known that tip clearance flows reduce the pressure rise, flow range and efficiency of the turbomachinery. So, the clear understanding about flow fields in the tip region is needed to efficiently design the turbomachinery. The Navier-Stokes code with the proper treatment of the boundary conditions has been developed to analyze the three-dimensional steady viscous flow fields in the transonic rotating blades and a numerical study has been conducted to investigate the detail flow physics in the tip region of transonic rotor, NASA Rotor 67. The computational results in the tip region of transonic rotors show the leakage vortices, leakage flow from pressure side to suction side and their interaction with a shock. Depen ding on the operating conditions, toad distributions and the position of shock-wave on the blade surface are very different close to the blade tip of the transonic compressor rotor. The load distribution and the shock-wave position close to the blade tip had the close relationship with the starting position of leakage vortex and the direction of leakage flow.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2005년도 후기학술대회논문집
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• pp.230-231
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• 2005

As environmental problems are important, automotive industries are developing various techniques to prevent air pollution. One of these is Positive Crankcase Ventilation (PCV) system. It removes blowby gas which includes about 30% hydrocarbon of total generated quantity. In this system, a PCV valve is attached in a manifold suction tube to control the flow rate of blowby gas which generates differently according to various operating conditions of an automotive engine. As this valve is very important, designers are feeling to design it because of both small size and high velocity. For this reason, we numerically investigated to understand both spool dynamic motion and internal fluid flow characteristics. As the results, spool dynamic characteristics, i.e. displacement, velocity, acting force, increase in direct proportion to the magnitude of differential pressure and indicate periodic oscillating motions. And, the velocity at the orifice region decreases according to the increase of differential pressure because of energy loss which is caused by the sudden decrease of flow area at the orifice region and the increase of flow volume in the front of spool head. Finally, the mass flow rate at the outlet decreases with the increase of spool displacement. We expect that PCV valve designers can easily understand fluid flow inside a PCV valve with our visual information for their help.

• 대한기계학회논문집B
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• 제39권10호
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• pp.817-824
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• 2015

본 논문은 수직 오리피스 노즐의 유동 및 물질전달 특성에 대한 실험적 연구를 목적으로 한다. 구동유체 및 부유체의 유량, 용존산소 농도 그리고 소비 전력을 측정하였으며, 고속 카메라를 이용한 직접 촬영 기법으로 수직 혼합유동의 가시화 이미지를 획득하였다. 측정자료를 이용하여 질량비, 총괄 산소전달 계수 그리고 물질전달 성능계수를 도출하였다. 구동압력이 증가하면 질량비는 약간 감소하는 반면에, 산소전달 계수와 소비전력은 증가하였다. 구동압력이 증가하고 질량비가 작아지면, 기포의 미세화가 촉진되고 확산도가 증대되기 때문에 산소 전달율이 증가하였다.

• 한국가시화정보학회지
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• 제10권1호
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• pp.15-20
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• 2012

PCV(Positive Crankcase Ventilation) system is designed to remove blowby gas. In this system, a PCV valve is attached in a manifold suction tube to control the flow rate of blowby gas which generates various operating conditions of an automotive engine. As this valve plays a crucial role, the demand in its design is high owing to the small size and high velocity. For this reason, a numerical investigation was carried out to understand both the spool dynamic motion and internal fluid flow characteristics. As a result, the spool dynamic characteristics(i.e. displacement, velocity, acting force), increase in direct proportion to the magnitude of the pressure difference and indicate periodic oscillating motions. Moreover, the velocity at the orifice region decreases according to the increase in differential pressure due to energy loss caused by the sudden decrease of flow area at the orifice region and the increase of flow volume in front of the spool head. Finally, the mass flow rate at the outlet decreases with the increase of spool displacement.

• 대한조선학회논문집
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• 제41권4호
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• pp.9-16
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• 2004

In the cavitation tunnel, the first corner playes role for the flow direction to execute 90-degree turn. So, energy loss is serious, and the cavitation phenomena well occur in the guide vane surface. In this paper, the flow in the first corner was numerically calculated. From the calculation result, cavitation phenomena mainly occurred in the suction side of the last guide vane and vicinity that vane and tunnel wall adjoin each other. And bubbles occurred from all guide vanes if the flow velocity in the test section reaches the any critical value. We could analogize with our experience in the water tunnel that bubbles that occurred in time not vanish, and become miniature in the flow although the pressure recover. So, they circulate with flow in the tunnel, and come into view in the test section. Therefore, first corner must be designed for bubbles not to appear in the test section according to the flow condition like velocity and pressure demanded by the experiment. We analyzed flow in case that the first elbow configuration was redesigned and some of the existing guides vanes were eliminated. And we presented that first elbow can be easely designed for the improvement of tunnel performance through the computational analysis.

• 열처리공학회지
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• 제35권1호
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• pp.27-32
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• 2022

Microbubble technology has been widely applied in various industrial fields. Recently, research on many types of microbubble application technology has been conducted experimentally, but there is a limit in deriving the optimal design and operating conditions. Therefore, if the computational fluid dynamics (CFD) analysis of multiphase flow is used to supplement these experimental studies, it is expected that the time and cost required for prototype production and evaluation tests will be minimized and optimal results will be derived. However, few studies have been conducted on multiphase flow CFD analysis to interpret fluid flow in microbubble generators using swirl flow. In this study, CFD simulation of multiphase flow was performed to analyze the air-water mixing process and fluid flow characteristics in a microbubble generator with a dual-chamber structure. Based on the simulation results, it was confirmed that a negative pressure was formed on the central axis of rotation due to the strong swirling flow. And it could be seen that the air inside the suction tube was introduced into the inner chamber of the microbubble generator. In addition, as the high-speed mixed fluid collided with external water sucked by the negative pressure near the outlet, a large amount of microbubbles was ejected due to the shear force between the two flows flowing in opposite directions.

• 한국유체기계학회 논문집
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• 제15권1호
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• pp.58-63
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• 2012

Three dimensional unsteady numerical calculations were performed to investigate unsteadiness of the tip leakage flow in an axial compressor. The first stage of the four-stage low-speed research axial compressor was examined. Since this compressor has a relatively large tip clearance, the unsteadiness of the tip leakage flow is induced. Through the results from the unsteady calculations, the process of the induced unsteady tip leakage flow was investigated. It was shown that the leakage flow that occurred at a rotor blade tip clearance affected the pressure distribution on the pressure side near the tip of the adjacent blade, thus caused the fluctuation of the pressure difference between the pressure side and suction side. Consequently, the unsteady tip leakage flow was induced at the adjacent rotor blade. The unsteady feature of the tip leakage flow was changed as the operating point was moved. The interface between the tip leakage flow and the main flow only affected the trailing edge region at the design point whereas the interface influenced up to the leading edge at the low flow rate point. As the flow rate decreased, additionally, it was seen that the vortex size of the tip leakage flow increased and the relatively large length scale disturbance occurred. On the other hand, using frequency analysis, it was shown that the unsteadiness was not associated with the rotor speed and was about 40% of the blade passing frequency. This feature was explained in the rotor relative frame of reference, and the frequency decreased as the flow rate decreased.

• 대한기계학회논문집B
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• 제29권5호
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• pp.625-632
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• 2005

This paper describes the shape optimization of a stator blade in a single-stage transonic axial compressor. The blade optimization has been performed using response surface method and three-dimensional Navier-Stokes analysis. Two shape variables of the stator blade, which are used to define a stacking line, are introduced to increase an adiabatic efficiency. Data points for response evaluations have been selected by D-optimal design, and linear programming method has been used for an optimization on a response surface. Throughout the shape optimization of a stator blade, the adiabatic efficiency is increased to 5.8 percent compared to that of the reference shape of the stator. The increase of the efficiency is mainly caused by the pressure enhancement in the stator blade. Flow separation on the blade suction surface of the stator is also improved by optimizing the stator blade. It is noted that the optimization of the stator blade is also useful method to increase the adiabatic efficiency in the axial compressor as well as the optimization of a rotor blade, which is widely used now.

• 한국수소및신에너지학회논문집
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• 제28권3호
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• pp.308-314
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• 2017

Jet pump in automotive fuel tank module is used to deliver fuel to fuel pump so that the pump is operated without aeration in suction side. In this study, three dimensional simulation model of jet pump is developed to understand performance variation over design parameters. Performance of jet pump is also investigated experimentally in terms of operating pressures. The experimental data is used to verify the three dimensional simulation model of jet pump. Verification results show that the three dimensional simulation model of jet pump is about 1% error with experiment. The simulations are conducted in terms of throat ratio and primary flow induction angle. As the throat ratio is increased, the flux ratio is trade-off at 3 times of throat diameter. On the other hand, as primary flow induction angle is increased, vapor pressure inside the nozzle is decreased. In summary, the results show that liquid jet pump has to be optimized over design parameters. Additionally, high velocity of induced flow is able to evolve cavitation phenomena inside the jet pump.