• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.227-230
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• 2006

The method of mass flow rate measurement using a critical nozzle is well established in the flow satisfying ideal gas law. However, in the case of measuring high-pressure gas flow, the current method shows invalid discharge coefficient because the flow does not follow ideal gas law. Therefore an appropriate equation of state considering real gas effects should be applied into the method. The present computational study has been performed to give an understanding of the physics of a critical nozzle flow for high-pressure hydrogen gas and find a way for the exact mass flow prediction. The two-dimensional, axisymmetric, compressible Navier-Stokes equations are computed using a fully implicit finite volume method. The real gas effects are considered in the calculation of discharge coefficient as well as in the computation. The computational results are compared with the previous experimental data and predict well the measured mass flow rates. It has been found that the discharge coefficient for high-pressure hydrogen gas can be corrected properly adopting the real gas effects.

• 한국전산유체공학회지
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• 제15권3호
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• pp.39-45
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• 2010

The turbulent flows in a tunnel mock-up($10L{\times}0.5W{\times}0.25H$ m3 : scale reduction 1/20) with rectangular cross section were investigated. The instantaneous velocity fields of Re = 49,029, 89,571 were measured by the 2-D PIV system which is consisted of double pulsed Nd:Yag laser and the tracer particles in the straight-duct mock-up where the flows were fully developed. The mean velocity profiles were taken from the ensemble averages of 1,000 instantaneous velocity fields. Simultaneously, numerical simulations(RANS) were performed to compare with experimental data using STREAM code. Non-linear eddy viscosity model (NLEVM : Abe-Jang-Leschziner Eddy Viscosity Model) was employed to resolve the turbulent flows in the duct. The calculated mean velocity profiles were well compared with PIV results. In the log-law profiles, the experimental data were in good agreement with numerical simulations all the way to the wake region except the viscous sub-layer (near wall region).

• 대한기계학회논문집B
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• 제38권9호
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• pp.773-779
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• 2014

가스터빈 희박 예혼합 연소기에서 발생하는 연소 불안정 현상을 모델링하기 위해서는 화염의 동 특성에 대한 정량적, 정성적 분석이 필수적이다. 이를 위하여 화염전달함수가 전산유체역학을 통하여 모델링되었다. 기존 화염전달함수의 연구 결과로부터, 화염전달함수의 결과는 화염의 구조에 크게 의존하는 것으로 알려졌다. 본 연구에서는 실제 계측된 화염의 구조와 유사한 형상을 갖도록 열전달 조건을 최적화한 후, 동일 조건에서 화염전달함수가 모델링되었다. 화염의 형상을 정확하게 예측할 수 있다면, 이로부터 전달함수의 이득값과 위상차의 모델링 결과 역시 실험값과 유사한 거동을 확인할 수 있었다.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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• pp.172-179
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• 2004

Average Bi-directional flow tube was suggested to measure single and two phase flow rate. Its working principle is similar with Pilot tube, however, it makes it possible to eliminate the cooling system which is normally needed to prevent from flashing in the pressure impulse line of Pilot tube when it is used in the depressurization condition. The suggested instrumentation was tested in the air-water vertical test section which has 80mm inner diameter and 10m length. The flow tube was installed at 120 of L/D from inlet of test section. From the test, single air and water flow rate was measured successfully. For the emasurement of two phase flow rate, Chexal drift-flux correlation was used. In the test a new correlation of momentum exchange factor was suggested. The test result shows that the suggested instrumentation using the measured void fraction and Chexal drift-flux correlation can predict the mass flow rates within $10\%$ error of measured data.

• 동력기계공학회지
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• 제4권4호
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• pp.32-40
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• 2000

A study on the fluid flow with ultrasonic forcing was carried out to get the enhancement of turbulence by laying emphasis on the ultrasonic incidence angles and reflectors. A large water tank was made of the transparent acrylic plates and city water of $25^{\circ}C$ was used as working fluid. 7 angles ($30^{\circ},\;45^{\circ},\;60^{\circ},\;90^{\circ},\;120^{\circ},\;135^{\circ},\;150^{\circ}$) as the ultrasonic incidence angle and 4 materials (wood, acryl, glass, iron) as the reflector were selected arid experiments for the above were made. The velocity vector distribution, kinetic energy and turbulence intensity of the turbulence flow fields enhanced by ultrasonic forcing were measured, compared and discussed by using the PIV measurement which was possible to measure the velocities of simultaneous multipoints. In results, it was cleared that the incidence angle of ultrasonic and material of reflector influenced the enhancement of turbulence.

• 한국유체기계학회 논문집
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• 제9권1호
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• pp.9-18
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• 2006

In the range of very low specific speed ($n_s<0.25$, non-dimensional), the performance of a centrifugal pump is much different from that of a centrifugal pump of normal ns and the efficiency of the pump drops rapidly with the decrease of $n_s$. In order to examine the reason of unstable performance characteristics of the very low $n_s$- centrifugal pump, the internal flow of the pump with a semi-open impeller is measured by a PTV(Particle Tracking Velocimetry) system. The purpose of this study is to make clear the internal flow characteristics and to obtain basic knowledge of the pump performance. The results show that the leakage flow through tip clearance give a strong effect on the flow pattern of impeller passage. A large vortex in the impeller passage and a strong reverse flow at impeller outlet are formed in the range of small flow rates, and the vortex and the reverse flow together reduce the absolute tangential velocity at the impeller outlet and cause the performance instability.

• 한국해양공학회지
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• 제14권4호
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• pp.9-16
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• 2000

This paper deals with the numerical and experimental study on the characteristics of the flow around a sunken vessel. Numerical simulation of the two dimensional steady flow on the midship section are carried out by the CFD code which is developed by using finite volume method and which includes the standard $textsc{k}$-$\varepsilon$ model with standard wall function. A experimental study is also carried out for the 1/100 scale model in circulating water channel. A velocity fields around the ship are measuremed by using particle image velocimetry technique. And the fluid forces acting on the ship hull by uniform current are measured by two axis load cell. The computed and measured velocity fields on the midship section are compared with each other in the view point of velocity dstribution and reattachement length, which shows good agreement in quality. The drag force on the vessel also showed the same tendency in both computational and experimental results. However, the quantitative disagreements are shown due to the three dimensional effect of the experiment. The result are used to determine the functional efficiency and stability of the vessel as a artificial reef.

• 대한조선학회논문집
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• 제28권2호
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• pp.118-131
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• 1991

자유수면 근처에서의 박리유동 현상을 수치 시뮬레이션 방법과 유선 가시화 시험 방법으로 연구하였다. 수치 시뮬레이션은 물체표면에서 유기되고 확산(diffusion) 및 대류(convection)에 의해 유동중으로 박리되어 방출되는 보오티시티(vorticity)를 다수의 보오텍스로 치환하여 유동의 변화와 유체력을 구하는 보오텍스블럽 법을 사용하여 수행하였다. 이 방법으로 대규모의 와류의 생성 및 변화를 추정할 수 있으며 또한 자유수면과 와류유동의 상호간섭현상 그리고 동 유체력 등을 추정할 수 있었다. 유선 가시화 시험은 해사기술연구소의 공동수조에서 수행하였으며, 직류 전원에 의해 얻어진 수소기포를 가시화 입자로 이용하였다. 조명장치는 할로겐 램프를 이용하였고, 연속사진을 가시화의 결과로 사용하였다. 또한 자유수면의 시간적 공간적 변화를 파고계를 이용하여 계측하고 이로부터 와류유동의 변화 주기를 추정하였다.

• 설비공학논문집
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• 제11권6호
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• pp.749-757
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• 1999

Holographic interferornetric tomography can provide reconstruction of instantaneous three dimensional gross flow fields. The technique however confronts ill-posed reconstruction problems in practical applications. Experimental data are usually limited in projection and angular scanning when a field is captured instantaneously or under the obstruction of test models and test section enclosures. An algorithm, based on a series expansion method, has been developed to improve the reconstruction under the ill-posed conditions. A three-dimensional natural convection flow around two interacting isothermal cubes is experimentally investigated. The flow can provide a challenging reconstruction problem and lend itself to accurate numerical solution for comparison. The refractive index fields at two horizontal sections of the thermal plume with and without an opaque object are reconstructed at a limited view angle of 80" The experimental reconstructions are then compared with those from numerical calculation and thermocouple thermometry. It confirms that the technique is applicable to reconstruction of reasonably complex, three-dimensional flow fields.elds.

• 해양환경안전학회지
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• 제23권2호
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• pp.200-207
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• 2017

선박에서 제어판을 가지는 목적은 선박의 운동을 제어하는데 있다. 제어판은 단동타의 형태일수도 있고 고정된 부분과 이동하는 부분의 조합에 의해 구성될 수도 있다. 이러한 제어판은 그 고유의 목적에 맞도록 역할을 수행하는 기능을 가지며, 유체와 상대적인 운동과 원초적인 기능에 의해 조정력을 증가시키는 것이다. 이러한 힘과 모멘트는 영각의 변화와 회전에 의해서 생성되고 선박의 조종성능을 결정한다. 본 논문에서는 플랩러더와 물분사러더의 2차원 유동특성을 회류수조에서 PIV기법을 이용하여 각각 계측하였다. 모델시험은 플랩러더와 물분사러더를 NACA0012의 영각과 플랩각을 변화시키면서 수행하였다. 2프레임 입자추적기법은 유동장에서 속도분포를 득하는데 이용되었다. 전체실험에서 레이놀즈수 $Re{\fallingdotseq}3.0{\times}10^4$를 적용하였으며 상호비교를 통해 계측된 결과값을 비교평가하였다.