• Title/Summary/Keyword: Reynolds Number

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Prediction of Turbulent Swirling Flow Using A Low-Reynolds-number Reynolds Stress Model (저레이놀즈수 레이놀즈응력모델을 이용한 난류선회류의 유동해석)

  • Kim J. H.;Kim K. Y.
    • Journal of computational fluids engineering
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    • v.6 no.4
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    • pp.35-42
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    • 2001
  • In this study, numerical calculations are carried out in order to evaluate the performance of low-Re Reynolds stress model based on SSG model for a swirling turbulent flow in a pipe. The results are compared with those of k-ε model, GL model and the experimental data. The results show that low-Re Reynolds stress model and GL model give better results than k-ε model. In the region near the wall, low-Re Reynolds stress model improves the predictions. However, there is no large difference between the predictions with two Reynolds stress models.

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A Study on the Near Wake of a Square Cylinder Using Particle Image Velocimetry (II)- Turbulence Characteristics - (PIV기법을 이용한정사각실린더의 근접후류에 관한 연구 (II)- 난류유동 특성 -)

  • Lee, Man-Bok;Kim, Gyeong-Cheon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.10
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    • pp.1417-1426
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    • 2001
  • Turbulent flow characteristics in the near wake of a square cylinder have been studied experimentally by using a Digital PIV method. Experiments are performed at the Reynolds numbers of 1600 and 3900 based on the free-stream velocity and the square height. The ensemble averaged turbulence statistics are acquired from 2030 realizations of instantaneous fluctuating velocity field after the conventional Reynolds decomposition. The differences in turbulent intensity and Reynolds shear stress profiles fur both oases indicate that the effect of Reynolds number seems to be descernible mainly due to the occurrence of transition in the separated shear layer. Because of the periodic nature of vortex shedding process, transverse velocity fluctuations contribute dominantly , to turbulent kinetic energy distribution. A comparison with previous LDV data obtained at much higher Reynolds number shows a fairly good agreement each other. It turns out that the effect of Reynolds number diminishes as increasing Reynolds number, which is a well-known feature of a sharp-edged bluff body wake. The streamwise variation of turbulence intensities are compared with those from a circular cylinder along the centerline at the same Reynolds number. The overall magnitudes and the decay rates of turbulence intensities are quite similar, but some differences are noticeble especially in the transverse intensity variation.

The Effect of Reynolds Number on the Three-Dimensional Flow Measurements with a Two-Stage Cone-Type Five-Hole Probe in a Non-Nulling Mode (Reynolds 수가 2단 원추형 5공프로브를 이용한 3차원 유동 측정에 미치는 영향 - 저속 유동장에서의 보정 결과 -)

  • Lee, Sang-U;Jeon, Sang-Bae
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.1
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    • pp.27-38
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    • 2002
  • The effects of Reynolds number on the non-nulling calibrations of a cone-type ave-type probe in low-speed flows have been investigated at Reynolds numbers of 2.04$\times$10$^3$, 4.09$\times$10$^3$and 6.13$\times$10$^3$. The calibration is conducted at the pitch and yaw angles in ranges between -35 degrees and 35 degrees with an angle interval of 5 degrees. In addition to the calibration coefficients, reduced pitch and yaw angles, static and total pressures, and velocity magnitude are obtained through a typical non-nulling reduction procedure. The result shows that each calibration coefficient, in general, is a function of both the pitch and yaw angles, so that the pre-existing calibration data in a nulling mode are not enough in accounting far the full non-nulling calibration characteristics. Due to interference of the probe stem, the calibration coefficient are more sensitive to Reynolds number at positive pitch angles than at negative ones. The calibration data reduced in this study may serve as a guide line in the estimation of uncertainty intervals resulted from the Reynolds number effects at low Reynolds numbers.

A Study on the Inlet Pressure Build-Up at Bearing Entrance (베어링 입구에서 발생하는 선단압력에 관한 연구)

  • 김종수;김경웅
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.8
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    • pp.1921-1930
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    • 1993
  • In order to evaluate the inlet pressure correctly, the full Navier-Stokes equations are solved numerically for the computational domain which covers the cavity region between pads as well as the bearing film. A nonuiform grid system is adopted to reduce the number of grid points, and the numerical solutions are obtained for a wide range of Reynolds number in laminar regime with various values of the distance between pads. The numerical results show that the inlet pressure is significantly affected by Reynolds number and the distance between pads. An expression for the loss coefficient in terms of Reynolds number and non-dimensional distance between pads is obtained on the basis of the numerical results. It is found that the inlet pressure over the whole range of numerical solutions can be fairly accurately estimated by applying the formula for the loss coefficient to the extended Bernoulli equation.

Experimental investigation on flow field around a flapping plate with single degree of freedom

  • Hanyu Wang;Chuan Lu;Wenhai Qu;Jinbiao Xiong
    • Nuclear Engineering and Technology
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    • v.55 no.6
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    • pp.1999-2010
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    • 2023
  • Undesirable flapping motion of discs can cause the failure of swing check valves in nuclear passive safety systems. Time-resolved particle image velocimetry (PIV) was employed to investigate the flow characteristics around a free-to-rotate plate and the motion response, with the Reynolds numbers, based on the hydraulic diameter of the channel, from 1.32 × 104 to 3.95 × 104. Appreciable flapping motion (±3.52°) appeared at the Reynolds number of 2.6 × 104 with the frequency of 5.08 Hz. In the low-Reynolds-number case, the plate showed negligible flapping. In the high-Reynolds-number case, the deflection angle increased with reduced flapping amplitude. The torque from the fluid determined the flapping amplitude. In the low-Reynolds-number case, Karman vortices were absent. With increasing Reynolds numbers, Karman vortices developed behind the plate with larger deflection angles. Strong interaction between the wake flow from the leading and trailing edge of the plate was observed. Based on power spectrum density (PSD) analysis, the vortex shedding frequency coincided with the flapping frequency, and the amplitude was positively correlated to the strength of the vortices. Proper orthogonal decomposition (POD) modes evince that, in the case of appreciable motion, coherent structures exhibited a larger spatial scale, enhancing the magnitude of the external torque on the plate.

Forced Convection Cooling Across Rectangular Blocks in a Parallel Channel (블럭이 부착된 수평 유로에서의 강제대류 열전달 해석)

  • 조한승;유재석
    • Journal of Energy Engineering
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    • v.2 no.3
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    • pp.251-257
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    • 1993
  • The purpose of this study is to obtain an improved interpretation of heat transfer phenomena between blocks and fluids in the parallel conducting plates. Flow is two-dimensional, incompressible steady laminar flow over rectangular blocks, representing finite heat source on parallel plate. Heat transfer phenomena, temperature of blocks and heat transfer into the flow field are investigated for different spacings between blocks and Reynolds numbers. Results indicate that Nusselt number on the far upstream corner of the block was higher than that of any part of the block. As Reynolds number and spacings of blocks increased, Nusselt number increased. The distribution of local Nusselt number on the top surface of the conducting plate is similar to the case with insulated plate. Temperature of the block which has heat source in half cubage was approximately twice as high as temperature of the block which has heat source in whole cubage. As Reynolds number and spacings of blocks increased, overall temperature decreased. The peak value of block temperature occurred at position shifted to the right or upper right from center. The maximum temperature of block can be expressed as a function of Reynolds number, spacings between blocks, position of maximum temperature of each block and then it is possible to predict the maximum temperature of blocks.

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The Study of Turbulence Model of Low-Reynolds Number Flow (저 레이놀즈수 유동장에서의 난류모델에 관한 연구)

  • Yoo C.;Lee J. S.;Kim C.;Rho O. H.
    • 한국전산유체공학회:학술대회논문집
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    • 2004.03a
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    • pp.172-177
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    • 2004
  • In the present work, we have interests on the modification of parallel implemented with MPI(Message Passing Interface) programming method, 3-Dimensional, unsteady, incompressible Navier-Stokes equation solver to analyze the low-Reynolds number flow In order to accurate calculation aerodynamic coefficients in low-Reynolds number flow field, we modified the two-equation turbulence model. This paper describes the development and validation of a new two-equation model for the prediction of flow transition. It is based on Mentor's low Reynolds $\kappa-\omega$ model with modifications to include Total Stresses Limitation (TSL) and Separation Transition Trigger (STT)

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REYNOLDS NUMBER EFFECTS ON TURBULENT PIPE FLOW PART I. MEAN FLOW FIELD AND LOW-ORDER STATISTICS (난류 파이프 유동에서의 레이놀즈 수 영향: Part I. 평균 유동장 및 저차 난류통계치)

  • Kang, Chang-Woo;Yang, Kyung-Soo
    • Journal of computational fluids engineering
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    • v.16 no.4
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    • pp.28-38
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    • 2011
  • Large eddy simulation(LES) of fully developed turbulent pipe flow has been performed to investigate the effect of Reynolds number on the flow field at $Re_{\tau}$=180, 395, 590 based on friction velocity and pipe radius. A dynamic subgrid-scale model for the turbulent subgrid-scale stresses was employed to close the governing equations. The mean flow properties, mean velocity profiles and turbulent intensities obtained from the present LES are in good agreement with the previous numerical and experimental results currently available. The Reynolds number effects were observed in the mean velocity profile, root-mean-square of velocity fluctuations, Reynolds shear stress and turbulent viscosity.

A Study on Critical Reynolds Numbers of Two-Dimensional Closed Cavity by CFD (CFD에 의한 2차원 밀폐캐비티의 임계레이놀즈수에 관한 연구)

  • 김진구;조대환;이영호
    • Journal of Ocean Engineering and Technology
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    • v.11 no.4
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    • pp.122-129
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    • 1997
  • Flow characteristics of two-dimensional closed square cavities near unsteady critical Reynolds numbers were studied numerically at five Reynolds numbers : 8${\times}10^3$, 8.5${\times}10^3$, 9${\times}10^3$, 9.5${\times}10^3$ and $10^4$ were investigated. A convection conservative difference scheme based upon SOLA to maintain the nearly 2nd-order spatial accuracy was adopted on irregular grid formation. Irregular grid number is 80${\times}$80 and its minimum size is about 1/400 of the cavity height(H) and its maximum is about 1/53 H. The result shows that the critical Reynolds number indicating the emergence of flow unsteadiness exists near Re=8.5${\times}10^3$ and their flow patterns reveal periodic fluctuation during transient and fully-developed stages.

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Flow Characteristics of Two-Dimensional Closed Cavity near Unsteady Critical Reynolds Numbers (2차원의 밀폐캐비티의 비정상 임계레이놀즈수 근방의 유동특성)

  • Kim, Jin-Gu;Kim, Chun-Sik;Lee, Yeong-Ho
    • Journal of Advanced Marine Engineering and Technology
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    • v.20 no.5
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    • pp.22-29
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    • 1996
  • Flow characteristics of two-dimensional closed square cavities near unsteady critical Reynolds numbers were studied numerically at four Reynolds numbers : $8{\times}10^3,\;8.5{\times}10^3,\;9{\times}10^3\;and\;9.5{\times}10^3.$ A convection conservative difference scheme based upon SOLA to maintain the nearly 2nd-order spatial accuracy is adopted on irregular grid formation. Irregular grid number is $80{\times}80$ and its minimum size is about 1/400 of the cavity height(H) and its maximum is about 1/53 H. The result shows that the critical Reynolds number indicating the emergence of flow wnsteadiness is ranging from Re=$8{\times}10^3\;to\;8.5{\times}10^3$ and their flow patterns reveal periodic fluctuation during transient and fully developed stages. But macroscopic flow behavior in terms of instantaneous and time-mean characteristics represent remarkable difference.

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