• Title/Summary/Keyword: Mean flow field

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Experimental Study on Flow Noise Generated by Axisymmetric Boundary Layer ( I ) - Wall Pressure Fluctuations on Axisymmetric Noses and on a Cylinder in an Axial Flow - (축대칭 물체의 경계층 유동소음에 대한 실험적 연구 ( I ) - 축대칭 물체 전두부 및 실린더 벽면 섭동압력 -)

  • Lee, Seung-Bae;Kim, Hooi-Joong;Kwon, O-Sup;Lee, Sang-Kwon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.7
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    • pp.945-956
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    • 2000
  • The axisymmetric bodies considered in this study have hemispherical and ellipsoidal noses. The near-field pressure fluctuations over each nose model at $Re_D=2.43{\times}10^5$ were investigated in the laminar separation region and developing turbulent boundary layers using a 1/8' pin-holed microphone sensor. The wall pressure fluctuations were also measured in an axisymmetric boundary layer on a cylinder parallel to mean flow at a momentum thickness Reynolds number of 850 and a boundary layer thickness to cylinder radius ratio of 1.88.

A Field Test on the Steady State Thermal Performance for the Forced Convection of Large Size Electric Air Heater (대형 전기온풍기 정상상태 열적성능의 현장시험에 관한 연구)

  • 최창용;김홍건
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • 2002.10a
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    • pp.99-103
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    • 2002
  • A field test was peformed to estimate the thermal performance of the forced convection electric air heater by the experiment. Air temperature, flow rate and electrical power input were measured with the related measurement sensors, and acquisition methods for the measured data were studied to effectively estimate the thermal performance of the tested air heater. To determine the mean air temperature at the flow cross-section, measuring positions were chosen by considering the flow velocity profile and the equally divided cross-sectional area. From the experimental results, thermal efficiency is obtained as an indication of the tested electric air heater performance.

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Effect of Multi-directional Random Waves on Characteristics of 3-D Wave Field around Permeable Submerged Breakwaters (다방향 불규칙파가 투과성 잠제 주변의 3차원 파동장에 미치는 영향)

  • Hur, Dong-Soo;Lee, Woo-Dong
    • Journal of Ocean Engineering and Technology
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    • v.26 no.2
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    • pp.68-78
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    • 2012
  • This study proposes an improved 3-D model that includes a new non-reflected wave generation system for oblique incident and multi-directional random waves, which enables us to estimate the effect of the various wave-types on 3-D wave fields in a coastal area with permeable submerged breakwaters. Then, using the numerical results,the three-dimensional wave field characteristics around permeable submerged breakwaters are examined in cases of oblique incident and multi-directional random waves. Especially, the wave height, mean surface elevation and mean flow around the submerged breakwaters are discussed in relation to the variation of incident wave condition.

Numerical Analysis of Tip Leakage Flows in Axial Flow Turbine Rotors (축류터빈 동익 내부의 누설유동에 관한 수치해석)

  • Chung, H.T.
    • Journal of Power System Engineering
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    • v.9 no.1
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    • pp.23-29
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    • 2005
  • Numerical analysis of three-dimensional viscous flow-fields in the turbine rotor passages was carried out to investigate flow physics including the interaction between secondary vortices, tip leakage vortex, and the rotor wake. The blade tip geometry was accurately modeled adopting the embedded H grid system. An explicit four-stage Runge-Kutta scheme was used for the time integration of both the mean flow and turbulence equations. The computational results for the entire turbine rotor flows, particularly the tip clearance flow and the secondary flows, were interpreted and compared with the experimental data from the Penn State turbine stage. The predictions for major features of the flow field have been found to be in good agreement with the experimental data.

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A study on the dynamic instabilities of a smart embedded micro-shell induced by a pulsating flow: A nonlocal piezoelastic approach

  • Atabakhshian, Vahid;Shooshtaria, Alireza
    • Advances in nano research
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    • v.9 no.3
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    • pp.133-145
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    • 2020
  • In this study, nonlinear vibrations and dynamic instabilities of a smart embedded micro shell conveying varied fluid flow and subjected to the combined electro-thermo-mechanical loadings are investigated. With the aim of designing new hydraulic sensors and actuators, the piezoelectric materials are employed for the body and the effects of applying electric field on the stability of the system as well as the induced voltage due to the dynamic behavior of the system are studied. The nonlocal piezoelasticity theory and the nonlinear cylindrical shell model in conjunction with the energy approach are utilized to mathematically modeling of the structure. The fluid flow is assumed to be isentropic, incompressible and fully develop, and for more generality of the problem both steady and time dependent flow regimes are considered. The mathematical modeling of fluid flow is also carried out based on a scalar potential function, time mean Navier-Stokes equations and the theory of slip boundary condition. Employing the modified Lagrange equations for open systems, the nonlinear coupled governing equations of motion are achieved and solved via the state space problem; forth order numerical integration and Bolotin's method. In the numerical results, a comprehensive discussion is made on the dynamical instabilities of the system (such as divergence, flutter and parametric resonance). We found that applying positive electric potential field will improve the stability of the system as an actuator or vibration amplitude controller in the micro electro mechanical systems.

Experimental study of unsteady thermally stratified flow (비정상 열확산 현상 의 실험적 연구)

  • 이상준;정명균
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.9 no.6
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    • pp.767-776
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    • 1985
  • Unsteady thermally stratified flow caused by two-dimensional surface discharge of warm water into a oblong channel was investigated. Experimental study was focused on the rapidly developing thermal diffusion at small Richardson number. The basic objective were to study the interfacial mixing between a flowing layer of warm water and an underlying body of cold water and to accumulate experimental data to test computational turbulence models. Mean velocity field measurements were carried out by using NMR-CT (Nuclear Magnetic Resonance-Computerized Tomography). It detects quantitative flow image of any desired section in any direction of flow in short time. Results show that at small Richardson number warm layer rapidly penetrates into the cold layer because of strong turbulent mixing and instability between the two layers. It is found that the transfer ofheat across the interface is more vigorous than that of momentum. It is also proved that the NMR-CT technique is a very valuable tool to measure unsteady three dimensional flow field.

Micro Holographic PTV Analysis of Three-dimensional Dean Flows in a Curved Micro-tube (마이크로 홀로그래픽 PTV를 이용한 미세곡관 내부 Dean 유동의 3차원 유동해석)

  • Kim, Seok;Lee, Sang-Joon
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03b
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    • pp.689-690
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    • 2008
  • In the present study, a micro holographic PTV (HPTV) system was used to experimentally investigate the structure of 3D flow within a curved micro-tube with varying Dean number. The employed HPTV system incorporated a high-speed digital camera to measure the temporal evolution of the 3D velocity fields of micro-scale fluid flows. With increasing Dean number, flow in the curved tube is transformed from a steady flow to a secondary flow with two counter-rotating vortices. In this study, to analyze the 3D flow characteristics in the curved section of tube at a high Dean number, the trajectories of fluid particles were obtained experimentally using the whole 3D velocity field data obtained by the micro HPTV technique. The mean velocity field distribution was then obtained by ensemble averaging the instantaneous velocity fields. These results would be helpful in the design of various passages within micro-scale devices or micro-chips and in understanding the mixing phenomena that occur in curved conduits along the trajectories of fluid particles.

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A Study on the Mixing Characteristics in Complex Turbulent Flow by a Laser Induced Fluorescence Method (레이저 형광여기법(LIF)를 이용한 복잡 난류유동장의 혼합특성에 관한 연구)

  • Kim, Kyung-Chun;Jeong, Eun-Ho
    • Proceedings of the KSME Conference
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    • 2001.06e
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    • pp.542-547
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    • 2001
  • A non-intrusive Planar Laser-Induced Fluorescence(PLIF) technique was applied to study the turbulent mixing process in a Rushton turbine reactor. Instantaneous and ensemble averaged concentration fields are obtained by measuring the fluorescence intensity of Rhodamine B tracer excited by a thin Nd:Yag laser sheet illuminating the whole center plane of the stirred tank. The gray level images captured by a 14-bit cooled CCD camera can be transformed to the local concentration values using a calibration matrix. The dye injection point was selected at the tank wall with three quarter height (3/4H) from the tank bottom to observe the mixing characteristics in upper bulk flow region. There exist distinct two time scales: the rapid decay of mean concentration in each region after the dye infusion reflects the large scale mixing while the followed slow decay reveals the small scale mixing. The temporal change of concentration probability functions conjectures the two sequential processes in the batch type mixing. An inactive column of water existed above the impeller disk, in which the fluid rotates with the shaft but is isolated from the mean bulk flow.

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Reduction of Normal Shock-Wave Oscillations by Turbulent Boundary Layer Flow Suction (경계층 유동의 흡입에 의한 수직충격파 진동저감)

  • Kim, Heuy Dong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.22 no.9
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    • pp.1229-1237
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    • 1998
  • Experiments of shock-wave/turbulent boundary layer interaction were conducted by using a supersonic wind tunnel. Nominal Mach number was varied in the range of 1.6 to 3.0 by means of different nozzles. The objective of the present study is to investigate the effects of boundary layer suction on normal shock-wave oscillations caused by shock wave/boundary layer interaction in a straight duct. Two-dimensional slits were installed on the top and bottom walls of the duct to bleed turbulent boundary layer flows. The bleed flows were measured by an orifice. The ratio of the bleed mass flow to main mass flow was controlled below the range of 11 per cent. Time-mean and fluctuating wall pressures were measured, and Schlieren optical observations were made to investigate time-mean flow field. Time variations in the shock wave displacement were obtained by a high-speed camera system. The results show that boundary layer suction by slits considerably reduce shock-wave oscillations. For the design Mach number of 2.3, the maximum amplitude of the oscillating shock-wave reduces by about 75% compared with the case of no slit for boundary layer suction.

The Flow Characteristics of Parallel Plane Jets Using Particle Image Velocimetry Technique (I) - Unventilated Jet - (PIV기법을 이용한 병렬 평면제트의 유동특성 (I) - 유입이 제한된 제트 -)

  • Kim, Dong-Keon;Yoon, Soon-Hyun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.3
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    • pp.302-310
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    • 2003
  • Experiments were conducted to show the characteristics of the flow on unventilated parallel plane jets. Measurements of mean velocity components and turbulent intensities were carried out with a particle image velocimetry to investigate the flow field generated by the air issued from two identical plane parallel nozzles and mixed with the ambient air. The measurements range of these experiments were Reynolds number of 5300 based on the nozzle width and the cases of nozzle-to-nozzle distance were four times. six times and eight times the width of the nozzle. Results show that a recirculation zone with a sub-atmospheric static pressure was bounded by the inner shear layers of the individual jets and the nozzles plate. The positions. where maximum value of mean turbulent intensities and mean turbulent kinetic energy show, were at the same position with the merging point. The spread of jets in the merging region increases more rapidly than that of Jets in the converging and the combined region. As nozzle-to-nozzle distances were increased. it was shown that merging and combined lengths were shorter.