• Title/Summary/Keyword: Rotational Reynolds number

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Performance Evaluation of Rotational Flow of a 2×2 Microfluidic Centrifuge with varying Inlet Conditions and Chamber Sizes (마이크로 유체 원심분리기의 입구 조건과 챔버 크기에 따른 회전 유동 성능 평가)

  • Jeon, Hyeong Jin;Kwon, Bong Hyun;Kim, Dae Il;Kim, Hyung Hoon;Go, Jeung Sang
    • Journal of the Korean Society of Visualization
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    • v.12 no.1
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    • pp.43-48
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    • 2014
  • This paper describes the measurement of performance evaluation of rotational flow varying chamber size and Reynolds number. Through the experimental visualization of the flow rotation, the number and position of flow rotation in the $2{\times}2$ microfluidic centrifuge were examined. At a chamber width of 250${\mu}m$, single flow rotation was obtained over at a Reynolds number of 300, while at a chamber width of 500 ${\mu}m$, single flow rotation did not appear. For performance evaluation, the intensity in microchamber was measured during 20 sec. At a chamber width of 250 ${\mu}m$, performance of rotational flow increased as Reynolds number increased. However, the variation of intensity in microchamber remained unchanged at a chamber width of 500 ${\mu}m$. The numerical analysis showed that the threshold centrifugal acceleration to obtain rotational flow for ejected particles was 200g.

Heat transfer characteristics between a rotating flat plate and an impinging water jet (회전전열평판과 충돌수분류간의 열전달특성에 관한 실험적 연구)

  • 전성택;이종수;최국광
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.10 no.5
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    • pp.509-522
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    • 1998
  • An experimental investigation is reported on the heat transfer coefficient from a rotating flat plate in a round turbulent normally impinging water jet. Tests were conducted over a range of jet flow rates, rotational speeds, jet radial posetions with various combinations of three jet nozzle diameter. Dimensionless correlation of average Nusselt number for laminar and turbulent flow is given in terms of jet and rotational Reynolds numbers, dimensionless jet radial position. We suggested various effective promotion methods according to heat transfer characteristics and aspects. The data presented herein will serve as a first step toward providing the information necessary to optimize in rational manner the cooling requirement of impingement cooled rotating machine components.

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Three-dimensional Laminar Flow Past a Rotating Cylinder (회전하는 원형 실린더 주위의 층류 유동장에 관한 수치적 연구)

  • Lee, Yong-Suk;Yoon, Hyun-Sik;Doo, Jeong-Hoon;Ha, Man-Yeong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.33 no.11
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    • pp.827-833
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    • 2009
  • The present study numerically investigates three-dimensional laminar flow past a rotating circular cylinder placed in a uniform stream. For the purpose of a careful analysis of the modification of flow by the effect of the rotation on the flow, numerical simulations are performed at a various range of rotational coefficients ($0{\leq}{\alpha}{\leq}2.5$) at one Reynolds number of 300. As ${\alpha}$ increases, flow becomes stabilized and finally a steady state beyond the critical rotational coefficient. The 3D (three dimensional) wake mode of the stationary cylinder defined at this Reynolds number has been disorganized according to ${\alpha}$, which were observed by the visualization of 3D vortical structures. The variation of the Strouhal number is very weak when the wake pattern is changed according to the rotational coefficient. As ${\alpha}$ increases, the lift increases, whereas the drag decreases.

Three-dimensional Laminar Flow past a Rotating Cylinder (회전하는 원형 실린더 주위의 층류 유동장에 관한 수치적 연구)

  • Lee, Yong-Suk;Doo, Jeong-Hoon;Ha, Man-Yeong;Yoon, Hyun-Sik
    • Proceedings of the KSME Conference
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    • 2008.11b
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    • pp.2733-2737
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    • 2008
  • The present study numerically investigates three-dimensional laminar flow past a rotating circular cylinder placed in a uniform stream. For the purpose of a careful analysis of the modification of flow by the effect of the rotation on the flow, numerical simulations are performed at a various range of rotational speeds($0{\leq}{\alpha}{\leq}2.5$) at one Reynolds number of 300. As $\alpha$ increases, flow becomes stabilized and finally a steady state beyond the critical rotational speed. The 3D (three dimensional) wake mode of the stationary cylinder defined at this Reynolds number has been disorganized according to $\alpha$, which were observed by the visualization of 3D vortical structures. The variation of the Strouhal number is significant when the wake pattern is changed according to the rotational speed. As $\alpha$ increases, the lift increases, whereas the drag decreases.

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A new rotational force model for quasi-steady theory of plate-like windborne debris in uniform flow

  • Lin, Huatan;Huang, Peng;Gu, Ming
    • Wind and Structures
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    • v.35 no.2
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    • pp.109-120
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    • 2022
  • The force coefficients of rotating plates in the acceleration stage will vary with rotation rate from 0 to stable rotation rate w0, which are important for quasi-steady theory of plate-like windborne debris to simulate the trajectory. In this paper, a wind tunnel experiment is carried out to study the effects of geometry and the Reynolds number on the variations of mean force coefficients of rotating plates. The rotational lift coefficients are sensitive to both geometry effect and Reynolds number effect, while the rotational drag and moment coefficients are only sensitive to geometry effect. In addition, new empirical formulas for the rotational lift coefficient and moment coefficients are proposed. Its accuracy is verified by comparing the predicted results with existing test data. Based on the experimental data of rotating plates, a new rotational force model for quasi-steady theory, which can be applied to a wider scope, is proposed to calculate the trajectory of plate-like windborne debris. The results show that the new model provides a better match with the tested trajectories than previous quasi-steady theories.

Measurement of Reynolds Number Effects on Cavitation Performance in a Turbopump Inducer (레이놀즈 수가 터보펌프 인듀서 캐비테이션 성능에 미치는 영향 측정)

  • Kim, Junho;Song, Seung Jin
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2017.05a
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    • pp.820-823
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    • 2017
  • This study experimentally investigate how the Reynolds number affect cavitation performance in a turbopump inducer using water. Cavitation performance has been determined by the static pressure measured at the inlet of the inducer. Reynolds number has been varied by varying water temperature and inducer rotational speed to maintain constant non-dimensional thermal parameter. At low non-dimensional thermal parameter, the critical cavitation number is insensitive to Reynolds number. However, at high non-dimensional thermal parameter, the critical cavitation number increased as Reynolds number increases. Thus, cavitation performance is deteriorated as Reynolds number increases when thermal effect exists.

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Experimental Study on the Helical Flow Field in a Concentric Annulus with Rotating Inner Cylinders (안쪽축이 회전하는 환형관내 헬리컬 유동장의 실험적 연구)

  • Hwang, Young-Kyu;Kim, Young-Ju
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.6
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    • pp.822-833
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    • 2000
  • This experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure drops and skin-friction coefficients have been measured for the fully developed flow of water and that of glycerine-water solution (44%) at a inner cylinder rotational speed of $0{\sim}600$ rpm, respectively. The transitional flow has been examined by the measurement of pressure drops and the visualization of flow field, to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients and to understand the flow instability mechanism. The present results show that the skin-friction coefficients have the significant relation with the Rossby numbers, only for laminar regime. The occurrence of transition has been checked by the gradient changes of pressure drops and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, it is gradually declined for turbulent flow regime. Consequently, the critical (axial-flow) Reynolds number decreases as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the excitation of taylor vortices.

Study on the Analysis of Turbulent Flow in a Rotating Square Sectioned $90^{\circ}$ Curved Duct (회전하는 정사각단면 $90^{\circ}$곡관내 난류유동에 관한 수치해석적 연구)

  • 이건휘;최영돈
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.9
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    • pp.2206-2222
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    • 1995
  • In this study, the characteristics of the three-dimensional turbulence flow in a rotating square sectioned 90.deg. bend were investigated by numerical simulation. And a dimensionless number, Coriolis force ratio, primarily subjected to the feature of the flow in the rotating 90.deg. bend was obtained as a result of one-dimensional theory. In the simulation study, low Reynolds number ASM developed by Kim(1991) in the square sectioned 180.deg. bend flow was modified in order to consider the rotational effects in the testing flows. In the near wall region of low Reynolds number, four turbulence models were employed and compared in order to find the most appropriate model for the analysis of the rotating 90.deg. bend flow. By comparison of the results with the experimental data, it is shown that low Reynolds number Algebraic Stress Model with rotating terms reflects most correctly the rotational effects. As the results of this study, centrifugal forces associated with the curvature of the bend and Coriolis forces and centripetal forces associated with the rotation affect directly both the mean motion and the turbulent fluctuations. Their actions on the mean flow are to induce a secondary motion while their effects on turbulence are to modify the pressure strain.

Experimental study on the helical flow field in a concentric annulus with rotating inner cylinders (안쪽축이 회전하는 환형관내 헬리컬 유동장의 실험적연구)

  • Hwang, Young-Kyu;Kim, Young-Ju
    • Proceedings of the KSME Conference
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    • 2000.04b
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    • pp.631-636
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    • 2000
  • The experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ration of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure drops and skin-friction coefficients have been measured for the fully developed flow of water and that of glycerine-water solution (44%) at a inner cylinder rotational speed of $0{\sim}600$ rpm, respectively. The transitional flow have been examined by the measurement of pressure drops and the visualization of flow field, to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients and to understand the flow instability mechanism. The present results show that the skin-friction coefficients have the significant relation with the Rossby numbers, only for laminar regime. The occurrence of transition has been checked by the gradient changes of pressure drops and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, is gradually declined for turbulent flow regime. Consequently, the critical (axial-flow) Reynolds number decreases as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the excitation of taylor vortices.

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A Study on the Axisymmetric Turbulent Boundaty Layer Over a Rotating Cone Submerged in a Free Stream (자유유동중에 놓인 회전하는 원추체 의 난류경계층 유동 에 관한 연구)

  • 박승호;이택식
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.7 no.3
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    • pp.278-285
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    • 1983
  • The momentum transfer in axisymmetric turbulent boundary layer over a rotating cone submerged in a free stream was studied by experiments and numerical analysis. In numerical analysis the velocity profiles were calculated by finite difference method using Prandtl mixing length concept, and the results were compared with experimental results. The agreement was good. By the numerical analysis the wall fircition coefficient was increased as the Reynolds number increased when the rotational speed is large, but the wall friction coefficient was decreased as the rotational speed increased.