• Title/Summary/Keyword: dimensionless velocity

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Flows Characteristics of Developing Turbulent Pulsating Flows in a curved Square Duct (곡관덕트내의 입구영역에서 난류 맥동유도의 유동특성)

  • 봉태근
    • Journal of Advanced Marine Engineering and Technology
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    • v.23 no.4
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    • pp.533-542
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    • 1999
  • In this study the flow characteristics of developing turbulent pulsating flows in a square-sec-tional 180。 curved duct are investigated experimentally. The experimental study of air flow in a square-sectional curved duct is carried out to measure axial velocity distribution secondary flow velocity profiles and wall shear stress distributions by using a Laser Doppler Velocimetry system with the data acquisition and processing system of Rotating Machinery Resolver (RMR) and PHASE software at the entrance region of the duct which is divided into 7 sections from the inlet(${{\o}}=0_{\circ}$) to the outlet (${{\o}}=180_{\circ}$) in $30_{\circ}$ intervals. The results obtained from the study are summarized as follows: (1) The time-averaged critical Dean number of turbulent pulsating flow(De ta, cr) is greater than $75{\omega}+$ It is understood that the critical Dean number and the critical Reynolds number are related to the dimensionless angular frequency in a curved duct. (2) Axial velocity profiles of turbulent pulsating flows are of an annular type similar to those of turbulent stead flows. (3) Secondary flows of trubulent pulsating flows are strong and complex at the entrance region. As velocity amplitudes(A1) become larger secondary flows become stronger. (4) Wall shear stress distributions of turbulent pulsating flows in a square-sectional $180_{\circ}$ curved duct are exposed variously in the outer wall and are stabilized in the inner wall without regard to the phase angle.

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Hydraulic Relation of Discharge and Velocity in Small, Steep Mountain Streams Using the Salt-dilution Method (Salt-dilution 방법을 이용한 산지소하천의 유량과 유속 관계 분석)

  • Yang, Hyunje;Lee, Sung-Jae;Im, Sangjun
    • Journal of Korean Society of Forest Science
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    • v.107 no.2
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    • pp.158-165
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    • 2018
  • Reach-average velocity prediction in steep mountain streams is important for understanding fluvial processes and practical applications of erosion control in mountain streams. little studies have been conducted in reach-average velocity, but hydraulic researches have been carried out to examine the relationship between discharge and reach-average velocity in torrent reaches using a relatively large amount of discharge data. In this study, a total of 87 data were measured in 8 torrent reaches. Salt-dilution method was used to estimate discharge. Reach-average velocity was calculated from harmonic mean of travel time that were measured by salt-dilution technique. In order to exlpore the hydraulic relation, both discharge and velocity were non-dimensionalized by using $D_{50}$, $D_{84}$, ${\sigma}_{pro}$ and $IPR_{90}$. It also indicated that ${\sigma}_{pro}$ and $IPR_{90}$ were good variables as roughness height for develop the relationship between non-dimensional discharge and velocity in mountain streams. Generally, reach-average velocity could increase exponentially as discharge increases.

Experimental analysis of the sedimentation processes in the movable weir by changing the channel slope considering weir operation (가동보 운영 및 하상경사 변화에 의한 보 상류 퇴사과정의 실험적 분석)

  • Lee, Kyung Su;Jang, Chang-Lae
    • Journal of Korea Water Resources Association
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    • v.51 no.8
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    • pp.729-737
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    • 2018
  • This study investigates the sediment processes the Improved-pneumatic-movable weir through laboratory experiments considering changing channel slopes. Experimental results show that the delta migrates towards the weir and the delta height increases as time passes. Moreover, as the delta approaches the weir, the delta migration speed decreases. As the dimensionless delta location increases, the effective height of dimensionless delta and the dimensionless reservoir capacity increases. Therefore, under the same slope conditions, the sediment deposition volume of the delta is small as the channel slope is mild. This means that the channel slope affects the development of the delta in the upstream of the Improved-pneumatic-movable weir. At the beginning of the experiment, the foreset slope is mild. However, the foreset slope of the delta increases with water depth as the delta migrates downstream. Moreover, as the slope is mild, the ratio of delta front length to delta height is close to 1, and the dimensionless delta height and the dimensionless delta migration speed decrease. As the delta height increases, the water depth, the velocity approaching to the weir and the delta migration speed decrease.

Vaporization Characteristics of Supercritical Hydrocarbon Fuel Droplet in Convective Nitrogen Environments (유동이 있는 초임계 질소 환경에서 탄화수소 연료 액적의 기화 특성)

  • Lim Jong-Hyuk;Lee Bong-Su;Koo Ja-Ye
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.10
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    • pp.1279-1287
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    • 2004
  • The vaporization characteristics of a liquid heptane droplet in a supercritical nitrogen flow are numerically studied. The transient conservation equations of mass, momentum, energy, and species are expressed in an axisymmetric coordinate system. The governing equations are solved time marching method with preconditioning scheme. The modified Soave-Redlich-Kwong equation of state is employed for taking account of real gas effects such as thermodynamic non-ideality and transport anomaly. Changing the convective velocity and ambient pressure, several parametric studies are conducted. The numerical results show that the two parameters, Reynolds number and dimensionless combined parameter(${\mu}$s/${\mu}$d)(equation omitted), have influence on supercritical droplet vaporization.

Non-dimensional analysis fo interior ballistics (공내탄도학의 무차원해석)

  • ;;Lee, Hung Joo;Min, Sung-Ki
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.1 no.3
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    • pp.125-130
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    • 1977
  • This is a dimensionless analysis of interior ballistics for the design of gun tube. One of the characteristics of this analysis is to ues the .ETA.$_{j}$ number which means a relative quantity of virtual work to the kimetic energy of projectile at the muzzle. In order to apply the concept of virtual work, it is assumed that the projectile is moved from the beginning to the end of bore under constant pressure of the certain travel distance of projectile. The principle of the analysis is induced from the Le Duc equation, which expresses velocity as a function of projectile travel and is based on the translation of a hyperbolic curve. From this non-dimensional analysis, the optimum design parameters of pressure in the bore, velocity and acceleration of projectile can be obtained from the table of figure without computation. This method was verified by the experimental work.k.

STEADY NONLINEAR HYDROMAGNETIC FLOW OVER A STRETCHING SHEET WITH VARIABLE THICKNESS AND VARIABLE SURFACE TEMPERATURE

  • Anjali Devi, S.P.;Prakash, M.
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.18 no.3
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    • pp.245-256
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    • 2014
  • This work is focused on the boundary layer and heat transfer characteristics of hydromagnetic flow over a stretching sheet with variable thickness. Steady, two dimensional, nonlinear, laminar flow of an incompressible, viscous and electrically conducting fluid over a stretching sheet with variable thickness and power law velocity in the presence of variable magnetic field and variable temperature is considered. Governing equations of the problem are converted into ordinary differential equations utilizing similarity transformations. The resulting non-linear differential equations are solved numerically by utilizing Nachtsheim-Swigert shooting iterative scheme for satisfaction of asymptotic boundary conditions along with fourth order Runge-Kutta integration method. Numerical computations are carried out for various values of the physical parameters and the effects over the velocity and temperature are analyzed. Numerical values of dimensionless skin friction coefficient and non-dimensional rate of heat transfer are also obtained.

A Study on Flow Characteristics of Developing Laminar Pulsating Flows in a Square Duct (정4각단면덕트 입구영역에서 층류맥동유동 유동특성에 관한 연구)

  • 박길문
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.5
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    • pp.1683-1696
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    • 1991
  • 본 연구에서는 정4각단면덕트 입구영역에서 층류맥동유동(laminar pulsating flows)의 유동특성을 이론 및 실험적으로 규명하기 위하여, 이론적 방법으로 덕트 입 구영역에서의 층류맥동유동에 대한 운동량방정식을 유도한 후 비선형인 대류항을 선형 화 시켜서 라플라스변환으로 속도분포식의 해를 구하였고, 실험적인 방법으로는 시험 덕트 크기는 횡단면의 가로*세로가 40mm*40mm이고, 길이가 4000mm인 정4각단면덕트 입구영역에서 송풍기에 의한 공기흡입유동으로 층류진동유동을 발생하며 이들 두유동 을 합성시켜 발생한 층류맥동유동에 대하여 열선유속계의 열선신호로부터 얻어진 속도 파형을 고찰하여 덕트내의 맥동유동에 대한 임계레이놀즈수를 결정하고 속도분포를 측 정하였다. 그리고 이론적으로 얻어진 속도분포식과 열선유속계로 측정한 속도분포를 비교검토하여 정확성을 검증하고, 이들 해석결과로 부터 층류맥동유동의 입구길이(en- trance lenght)식을 결정하여 제안하였다.

An Experimental Study on Inner Flow between Shrouded Corotating Disks (밀폐된 동시회전원판 내부유동에 관한 실험적 연구)

  • Yu, Seung-Chul;Joo, Won-Gu
    • Proceedings of the KSME Conference
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    • 2000.04b
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    • pp.637-643
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    • 2000
  • The shrouded corotating disk flow has a simple figure on geometric basis, but has various and complicated forms of flow. this complicated flows can be variously applied to not only information storage device, but also turbomachinery which is greatly influenced by centrifugal force. This study measured its velocity to measure inner flow field with unique flow field univluenced, using LDV and subminiature hot-wire. The result of experiment shows that distribution limits of solid body rotation region, dimensionless velocity gradient and distribution limits of disk surface boundary layer(Ekman layer) are changed by the gap of disks and rotating speed. Circulating vortex which is near the shroud is effected by the gap of disks and rotating speed.

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n Analysis of Elastohydrodynamic lubrication in Line Contacts-the effect of temperature variation (유체 온도 변화를 고려한 선 접촉면사이의 탄성유체윤활 해석)

  • 서민호;임윤철
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 2001.11a
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    • pp.364-373
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    • 2001
  • This paper describes the variation of lubricant's temperature effects on elastohydrodynamic lubrication. The Newton-Raphson technique was used to solve the simultaneous system of Reynolds and elasticity equations. To show effects of lubricant's temperature, average temperature across the oil film was calculated using the energy equation. Pressure distribution, film shape, and temperature distribution were obtained for fully flooded conjunctions, and various dimensionless speed parameters while load and material parameters were held constant. Minimum film thickness were obtained for various material properties while load and velocity were held constant. It is drawn that the thermal effects have a strong influence on a minimum film thickness under high rolling velocity and slip ratio.

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Two-Dimensional Analysis of Enthalpy Flow in a Pulse Tube (맥동관의 엔탈피유동에 대한 2차원 해석)

  • 백상호;장승철;정은수
    • Progress in Superconductivity and Cryogenics
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    • v.1 no.1
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    • pp.42-47
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    • 1999
  • Enthalpy transport in a pulse tube was investigated by two-dimensional analysis of mass. momentum an energy equations of the gas as well as energy conservation of the tube wall. The mean temperature of the gas and the tube wall was obtained directly by assuming that the outer surface of a pules tibe wall is adiabatic. Axial profile of mean temperature is small. but it deviates significantly from linear profile when the dimensionless frequency is large. Effect of operating frequency. tube wall thickness, velocity ratio and velocity phase angle between both ends of a pulse tube on net enthalpy flow were shown.

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