고속 헬륨 제트 유동의 실험적 분석을 위한 4차원 디지털 스펙클 토모그래피 기법 개발

고한서,김용재 한국수소및신에너지학회 2006 한국수소 및 신에너지학회논문집 Vol.17 No.3

A high-speed and initial helium jet flow has been analyzed by a developed four-dimensional digital speckle tomography. Multiple high-speed cameras have been used to capture movements of speckles in multiple angles of view simultaneously because a shape of a nozzle for the jet flow is asymmetric and the initial jet flow is fast and unsteady. The speckle movements between no flow and helium jet flow from the asymmetric nozzle controlled by a solenoid valve have been obtained by a cross-correlation tracking method so that those distances can be transferred to deflection angles of laser rays for density gradients. The four-dimensional density fields for the high-speed helium jet flow have been reconstructed from the deflection angles by a developed real-time tomography method.

압축성 대와류모사를 이용한 고속열차의 공력 및 공력소음의 수치적/실험적 분석

이권기,정철웅,김재환,정민승 한국음향학회 2024 韓國音響學會誌 Vol.43 No.1

Due to technological advances, the cruising speed of high-speed trains is increasing, and aerodynamic noise generated from the flow outside the train has been an important consideration in the design stage. To accurately predict the flow-induced noise, high-resolution generation of sound sources in the near field and low-dissipation of sound propagation in the far field are required. This should be accompanied by a numerical grid and time resolution that can properly consider both temporal and spatial scales for each component of the real high-speed train. To overcome these challenges, this research simultaneously calculates the external flow and acoustic fields of five high-speed train cars of real-scale and at operational running speeds using a three- dimensional unsteady Large Eddy Simulation technique. To verify the numerical analysis, the measurements of the wall pressure fluctuation and numerical results are compared. The Ffowcs Williams and Hawking equation is used to predict the acoustic power radiated from the high-speed train. This research is expected to contribute to noise reduction based on the analysis of the aerodynamic noise generation mechanism of high-speed trains.

LBM 기법을 이용한 고속열차 공기저항 전산해석

변성준(Sung Jun Byun),Stephane Cyr,김석원(Suk Won Kim),권혁빈(Hyeok-bin Kwon) 한국철도학회 2014 한국철도학회 학술발표대회논문집 Vol.2014 No.5

고속철도 차량의 공기저항과 유동 특성의 정확한 예측은 차량의 설계에 매우 중요한 요소이다. 본 연구에서는 고속열차 형상의 공기저항을 정량적으로 평가하기 위해 LBM(Lattice Boltzmann Method) 기법을 이용하여 4 량 편성의 1/20 축소형 HEMU-430X 고속열차 주위의 유동장에 대한 전산해석을 수행하였다. 해석에 사용된 프로그램은 자동차분야에서 공력과 유동해석에 많이 사용되고 있는 Exa Co.의 PowerFLOW이며, 실험에 사용된 속도 조건은 69.44 m/s로써 비압축성 난류 영역에 해당되어 비압축성 VLES(very large eddy simulation) 모델을 이용하였다. 전산해석을 통해 얻어진 열차의 공기저항계수는 풍동실험 결과와 비교하여 해석기법의 정확도를 평가하였으며, 열차 주위의 비정상 유동 특성 및 LBM 기법의 고속열차 적용 타당성에 대해서도 논하였다. For high-speed trains, estimation of aerodynamic drag as well as understanding of flow structure around trains is very important to design aerodynamic shape. In this study, LBM(Lattice Boltzmann Method) has been employed to assess the aerodynamic drag of high-speed train quantitatively, and numerical simulation around the high-speed train has been conducted. Incompressible VLES(Very Large Eddy Simulation) model has been used in simulating by PowerFLOW of Exa Co. in accordance with the flow Mach number about 0.2 which corresponds to freestream velocity 70m/s. The aerodynamic drag coefficient from numerical simulation has been compared with that from wind tunnel experiment to evaluate the accuracy of the numerical methods. The unsteady flow characteristics around high-speed train as well as the application of LBM to high-speed train have also been discussed.

Fundamental studies on free stream acceleration effect on drag force in bluff bodies

이영빈,노주현,김규홍,이동호 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.3

This paper describes fundamental studies on free stream acceleration effect on drag force in bluff bodies. The flow with gradual velocity increase assumed an accelerated flow. The wind tunnel tests were conducted in order to investigate the difference of aerodynamic characteristics between non-accelerated flow and accelerated flow. The experimental models were a circular cylinder and a square cylinder. In an accelerated flow, the condition of free stream was an acceleration of about 3.6m/s². Experimental Reynolds number varied between form 4.0×10⁴ to 1.64×10^5. The pressure distributions and the aerodynamic force were measured in both case of nonaccelerated flow and accelerated flow. In case of a circular cylinder, the drag of accelerated flow is lower than that of non-accelerated flow in the low Reynolds number regime. Then, it becomes higher than that of non-accelerated flow in the high Reynolds number regime. On the other hand, in case of a square cylinder, the drag of accelerated flow is higher than that of non-accelerated flow in the whole Reynolds number regime. If a separation point can be movable such as the circular cylinder, the additional momentum due to flow acceleration leads to delay separation and to decrease the drag in the low Reynolds number regime. If a separation point is nearly fixed such as a square cylinder, the additional momentum due to acceleration always affects to increase the drag than that of non-accelerated flow. Based on this research, it is expected that the roof shape of high speed train where the separation point is movable has the advantages to reduce the effect of accelerated flow such as strong crosswind/gust.

Experimental Study on the Mechanism of the Combined Action of Cavitation Erosion and Abrasion at High Speed Flow

X.Wang,Y. A. Hu,Z. H. Li 한국콘크리트학회 2020 International Journal of Concrete Structures and M Vol.14 No.1

A new experimental method on simulating the combined action of cavitation erosion and abrasion was proposed to investigate the erosion mechanism of overflow structure induced by the said processes. An automatic sand mixing device was invented for high-pressure and high-speed flow based on the characteristics of Venturi cavitation generator and hydraulic Bernoulli principle. The experimental system for the combined action of cavitation erosion and abrasion was designed and constructed, and high-speed sand mixing flow only appeared in the test section. A series of tests on the combined and single action of cavitation erosion and abrasion on hydraulic concrete and cement was carried out by using the invented experimental device. Results show that the wear of concrete surface exhibited the combined characteristics of cavitation erosion and abrasion under their joint action. The damage degree of concrete surface under the combined action was more severe than that under a single action. The mass loss of concrete under the combined action was higher than sum of mass losses of concrete under two single actions. The promotion and enhancement between cavitation erosion and abrasion existed in high-speed sand mixing flow. A power exponential relationship was observed between erosion mass loss and flow speed, and the velocity indexes approximated 4.5. Small and light sand particles easily follow water flow. Thus, the strong coupling effect of cavitation erosion and abrasion resulted from the presence of small sand particles. Given the different mechanisms of cavitation erosion and abrasion, presenting the skeleton structure formed by cavitation erosion was notably difficult under the action of abrasion. Meanwhile, abrasion wear easily occurred under the impact of cavitation erosion, and this result is due to the mechanism of the combined action of both processes.

유동해석을 통한 고속차량 오물수거 효율화 고찰

장진영,김재문 한국산학기술학회 2023 한국산학기술학회논문지 Vol.24 No.12

High-speed rail vehicles are generally maintained within a limited period between the end of operation and the next operation, including waste collection. The waste collection system for high-speed rail vehicles entails the centralized gathering of waste generated during operation into an internal tank. Subsequently, the accumulated waste is collected after the vehicle is stationed at the depot. The waste collection equipment within the current high-speed rail maintenance depot can experience increased operational time and issues, such as leaks due to aging and performance degradation from prolonged use. Accordingly, maintenance work on high-speed rail vehicles is influenced by the time required for waste collection tasks. Securing maintenance time by minimizing the duration of waste collection work is crucial for ensuring the safety and efficiency of vehicle operations. The waste collection system generates a vacuum in the waste collection well and collects it by sucking it from the tank installed in the vehicle to the waste collection well. In this process, the effects of distance, pipe thickness, and vacuum pressure. have a significant impact on efficiency. Therefore, to reduce the waste collection time, the efficiency must be verified under conditions appropriate for this environment. This paper considers the efficiency of high-speed vehicle waste collection through flow analysis of piping and vacuum.

Parametric Study on the Design of Turbocharger Journal Bearing - Aeration Effects

Chun, Sang-Myung Korean Tribology Society 2006 KSTLE International Journal Vol.7 No.2

Turbocharger bearings are under the circumstance of high temperature, moreover rotated at high speed. It is necessary to be designed overcoming the high temperature. So the type of oil inlet port, the inlet oil temperature and the sort of engine oil should be designed, controlled and selected carefully in order to reduce the bearing inside temperature. In this study, the influence of aerated oil on a high-speed journal bearing is also examined by using the classical thermohydrodynamic lubrication theory coupled with analytical models for viscosity and density of air-oil mixture in fluid-film bearing. Convection to the walls and mixing with supply oil and re-circulating oil are considered. The considered parameters for the study of bubbly lubrication are oil inlet port's type, oil aeration level and shaft speed. It is found that the type of oil inlet ports and shaft speed play important roles in determining the temperature and pressure, then the friction and load of journal bearing at high speed operation. Also, the results show that, under extremely high shaft speed, the high shear effects on aerated oil and the high temperature effects are canceled out each other. So, the bearing load and friction show almost no difference between the aerated oil and pure oil.

PIV System for the Flow Pattern Anaysis of Artificial Organs ; Applied to the In Vitro Test of Artificial Heart Valves

Lee, Dong-Hyeok,Seh, Soo-Won,An, Hyuk,Min, Byoung-Goo The Korean Society of Medical and Biological Engin 1994 의공학회지 Vol.15 No.4

The most serious problems related to the cardiovascular prothesis are thrombosis and hemolysis. It is known that the flow pattern of cardiovascular prostheses is highly correlated with thrombosis and hemolysis. Laser Doppler Anemometry (LDA) is a usual method to get flow pattern, which is difficult to operate and has narrow measure region. Particle Image Velocimetry (PIV) can solve these problems. Because the flow speed of valve is too high to catch particles by CCD camera, high-speed camera (Hyspeed : Holland-Photonics) was used. The estimated maximum flow speed was 5m/sec and maximum trackable length is 0.5 cm, so the shutter speed was determined as 1000 frames per sec. Several image processing techniques (blurring, segmentation, morphology, etc) were used for the preprocessing. Particle tracking algorithm and 2-D interpolation technique which were necessary in making gridrized velocity pronto, were applied to this PIV program. By using Single-Pulse Multi-Frame particle tracking algorithm, some problems of PIV can be solved. To eliminate particles which penetrate the sheeted plane and to determine the direction of particle paths are these solving methods. 1-D relaxation fomula is modified to interpolate 2-D field. Parachute artificial heart valve which was developed by Seoul National University and Bjork-Shiely valve was testified. For each valve, different flow pattern, velocity profile, wall shear stress and mean velocity were obtained.

A Study on Aero-Acoustics of High-Speed Turbomachinery for Different Rotational Speeds

송지훈(Ji-Hun Song),이동렬(Dong-Ryul Lee) Korean Society for Precision Engineering 2020 한국정밀공학회지 Vol.37 No.12

This study is to numerically investigate the Aero-Acoustics of Turbocharger compressor. The turbocharger compressor is high-speed turbomachinery that rotates faster than 200,000 RPM. The Aero-Acoustics with five different rotational speeds (120,000, 150,000, 180,000, 200,000, and 220,000 RPM) is used herein. The fluid domain is designed by CATIA V5R21 and analyzed by ANSYS FLUENT V19.1 with compressible momentum equation. The Pressure-velocity coupling method of the solver is the coupled algorithm and calculated by a pressure-based method. Numerical analysis of the aero-acoustics by broadband noise sources model provides calculated sound-source and acoustic-level based on steady RANS. At the industrial site, it is important to quickly analyze the noise source. APL (Acoustic Power Level) with five different rotational speeds and sound characteristics based on flow factor at the compressor wheel was numerically calculated for the noise-based design. The maximum APL is located at blade tips in case of 120,000, 150,000 and 180,000 RPM. In the case of 200,000 RPM, the maximum APL is located at splitter tips. At more than 220,000 RPM, the maximum APL is located at the balancing cutting section of the wheel. In order to optimally design the high-speed turbomachinery, cutting sections and side locations of the wheel are essential factors to reduce physical noise.

Secondary flow control using endwall jet fence in a high-speed compressor cascade

Huaping Liu,Shuai Jiang,Yongchuan Yu,Dongfei Zhang,Huanlong Chen 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.10

This paper proposes a secondary flow control concept using Endwall jet fence (EJF). A parametric investigation concerning the variations of the jet location along the axial and pitch-wise direction as well as the skew angle is conducted numerically to validate the potential of EJF in a high-speed compressor cascade with an inlet Mach number of 0.67. And then the interaction mechanisms between the EJF and the endwall secondary flow are discussed in detail. The results show that the EJF could reduce the corner separation and losses significantly by inputting transverse momentum component, inducing a concentrated jet vortex to block the pitch-wise migration of the passage vortex as well as enhancing the energy exchange between the endwall boundary layer and the mainstream. The jet location and the skew angle are important for the influence of EJF on the cascade performance. In this work, a maximum total pressure loss reduction of 11.6 % is obtained by the EJF located at 30 % of the axial chord and 10 % of the pitch with a skew angle of β = 40°, whereas the jetto-inflow mass flow ratio is only about 0.4 %, validating the high efficiency of this flow control concept. For the off-design points, the EJF also shows appreciable potential on the endwall secondary flow control and loss reduction.