• 한국가시화정보학회지
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• 제10권3호
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• pp.25-29
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• 2012

This paper introduces a new parameter to design the $2{\times}2$ microfluidic centrifuge with single flow rotation positioned at the center of microchamber. The dimensional centrifugal acceleration momentum flux which is defined as the interfacial momentum flux divided by distance from the center of the chamber explains the flow rotation and its threshold provides a reference to expect single flow rotation. Through the numerical and experimental visualization of the flow rotation, the number and position of flow rotation in the $2{\times}2$ microfluidic centrifuge were examined. At a channel width of $50{\mu}m$ and chamber width of $250{\mu}m$, single flow rotation was obtained over at a Reynolds number of 300, while at a channel width of $100{\mu}m$ and chamber width of $500{\mu}m$, single flow rotation did not appear. The numerical analysis showed that the threshold centrifugal acceleration momentum flux to obtain single flow rotation was $3500kg/m{\cdot}s^2$.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2248-2253
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• 2008

A numerical study on oscillatory thermocapillary flow in half-zone has performed to understand the effect of axial rotation. 2d unsteady code is developed to observe the onset of oscillation. 2cs Silicone oil with Prandtl number of 26.5 is used as a working fluid. The critical temperature difference at onset of oscillation is investigated under the different aspect ratios and rotation modes. It is shown that the onset of oscillation is delayed when aspect ratio reduces and rotating speed increases. The oscillatory flow is strongly reduced under top rotation and co-rotation modes, while it is augmented under bottom rotation and counter-rotation modes. It is thought that interaction between return flow and bottom wall is important to explain the oscillatory flow.

• Korea-Australia Rheology Journal
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• 제21권2호
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• pp.119-126
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• 2009

A numerical analysis is performed to investigate the effect of rotation on the blood flow characteristics with four different angular velocities. The artery has a cylindrical shape with 50% stenosis rate symmetrically distributed at the middle. Blood flow is considered a non-Newtonian fluid. Using the Carreau model, we apply the pulsatile velocity profile at the inlet boundary. The period of the heart beat is one second. In comparison with no-rotation case, the flow recirculation zone (FRZ) contracts and its duration is reduced in axially rotating artery. Also wall shear stress is larger after the FRZ disappears. Although the geometry of artery is axisymmetry, the spiral wave and asymmetric flow occur clearly at the small rotation rate. It is caused that the flow is influenced by the effects of the rotation and the stenosis at same time.

• 한국기계기술학회지
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• 제13권4호
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• pp.1-7
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• 2011

The paper concerns numerical study of fully developed laminar flow of a Newtonian water and non-Newtonian fluids, 0.2% aqueous of sodium carboxymethyl cellulose(CMC) solution in eccentric annuli with combined bulk axial flow and inner cylinder rotation. Pressure losses and skin friction coefficients have been measured when the inner cylinder rotates at the speed of 0~200 rpm. A numerical analysis considered mainly the effects of annular eccentricity and inner cylinder rotation. The present analysis has demonstrated the importance of the drill pipe rotation and eccentricity. In eccentricity of 0.7 of a Newtonian water, the flow field is recirculation dominated and unexpected behavior is observed. it generates a strong rotation directed layer, that two opposing effects act to create two local peaks of the axial velocity. The influences of rotation, radius ratio and working fluid on the annular flow field are investigated.

• 대한수학회보
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• 제36권4호
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• pp.707-716
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• 1999

In this pater we study the continuity of rotation numbers of liftings of circle maps with degree one. And apply our result to prove that a positively equicontinuous flow of homeomorphisms on the circle $S^1$ is topologically conjugate to a continuous flow of rotation maps.

• 대한물리의학회지
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• 제10권1호
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• pp.115-120
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• 2015

PURPOSE: Vertebrobasilar insufficiency (VBI) should be carefully assessed in patient for whom manipulation of the cervical spine is to be undertaken. The purpose of this study was to investigate the changes in posterior cerebral artery blood flow velocity following head and body positioning by transcranial doppler ultrasonography (TCD) in healthy subjects. METHODS: Twenty two healthy female (mean age $20.77{\pm}1.30yrs.$) participants volunteered to participate in the study. None of the participants had a history of neck pain or headache within the last 6 months. To evaluate the cerebral blood flow, we measured the mean flow velocity of the posterior cerebral artery unilaterally (right side). The blood flow velocity was measured under 3 different head positions (in a neutral head position, ipsilateral head rotation and contralateral head rotation position) and 2 different body conditions (supine position and sitting position). RESULTS: The mean blood flow velocity of posterior cerebral artery was decreased in body positioning from supine to sitting (p<.05), but the decreased rate of blood flow velocity in posterior cerebral artery did not change significantly between ipsilateral head rotation and contralateral head rotation (p>.05). CONCLUSION: These result of our study show that body positioning (sitting and supine) affect the blood flow velocity in posterior cerebral artery.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.83-86
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• 2002

Numerical simulations are conducted for laminar flow past a sphere rotating In the transverse direction, in order to investigate the effect of the rotation on the characteristics of flow over a sphere. The Reynolds numbers considered are Re=100, 250 and 300 based on the free-stream velocity and the sphere diameter, and the rotational speeds are in the range of $0{\leq}{\omega}{\leq}1$, where ${\omega}^{\ast}$ is the maximum velocity on the sphere surface normalized by the free-stream velocity. At ${\omega}^{\ast}=0$ (without rotation), the flow past the sphere experiences steady axisymmeoy, steady planar-symmetry and unsteady planar-symmetry, respectively, at Re=100, 250 and 300. However, with rotation, the flow becomes planar-symmetric for all the cases investigated and the symmetry plane is orthogonal to the axis of the rotation. The flow is also steady or unsteady depending on both the Reynolds number and the rotational speed, and the vortical structures behind the sphere are significantly modified by the rotation. For example, at Re=300, hairpin vortices completely disappear in the wake at ${\omega}^{\ast}=0.4\;and\;0.6$, and at ${\omega}^{\ast}=1$ vortical structures of a high frequency are newly generated due to the shear layer instability. It is also shown that with increasing rotational speed, the time-averaged drag and lift coefficients increase monotonically.

• 한국자기공명학회논문지
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• 제20권2호
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• pp.61-65
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• 2016

Undesirable convective flow in an NMR tube inhibits the accurate measurement of diffusion coefficients by NMR spectroscopy. To minimize the convection effects, various methods have been suggested, and it has been known that the use of sample rotation can be useful. However, it has not been clearly examined that the convection suppressing effect of the sample rotation under the different spinning speeds. In this study, the relation between convective flow and the sample rotation was investigated using PGSE NMR diffusion experiments to reveal the feasibility for controlling the convective flow in an NMR tube by sample rotation itself. The viscosity effect was also examined using solvents with four different viscosities, acetone-$d_6$ chloroform-d, pyridine-$d_5$, and $D_2O$. The sample rotation showed apparent convection suppressing effects at all temperature range for the low viscosity solvents, acetone-$d_6$ and chloroform-d, even at the faster than 5 Hz spinning rate. The similar patterns were also observed for pyridine-$d_5$ and $D_2O$, which have higher viscosity. This effect was observed even at high temperatures where convective flow arises conspicuously.

• Nuclear Engineering and Technology
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• 제53권7호
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• pp.2207-2220
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• 2021

Lead alloy is used as coolant in Lead-based cooled Fast Reactor (LFR). The natural characteristics of lead alloy are combined with the simple structural design of LFR. This constitutes the inherent safety characteristics of LFR. The main work of this paper is to take the main coolant pump (MCP) in the lead-cooled fast reactor (LFR) as the research object, and to study the flow pattern distribution of the internal flow field under the reverse rotation pump condition, the reverse rotation positive-flow braking condition and the reverse rotation negative-flow braking condition. In this paper, the double-outlet volute type and the space guide vane are selected as the potential designs of the CLEAR-I MCP. In this paper, the CFD method is used to study the potential reverse accident of the MCP. It is found that the highest flow velocity in the impeller appears at the impeller outlet, and the Q-H curves of the two design programs basically coincide. The space guide vane type MCP has better hydraulic performance under the reverse rotation positive-flow condition, the Q-H curves of the two designs gradually separate with increasing flow rate, and the maximum flow velocity inside the space guide vane type MCP is obviously lower than that of the double-outlet volute type. For the reverse rotation test of MCP, only the condition of the forward rotating pump of the main coolant pump is tested and verified. For the simulation of the MCP in LBE medium, it proved that the turbulence model and basic settings selected in the simulation are reliable.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.2095-2100
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• 2003

This Experimental study concerns the characteristics of vortex flow in a concentric annulus with a diameter ration of 0.52, whose outer cylinder is stationary and inner one is rotating. Pressure losses and skin-friction coefficients have been measured for fully developed flow of bentonite-water solution(5%) when the inner cylinder rotates at the speed $0{\sim}400rpm$. The results of present study reveal the relation of the bulk flow Reynolds number Re and Rossby number $R_o$ With respect to the skin friction coefficients. The effect of rotation on the skin friction coefficient is significantly dependent on the flow regime. In all flow regime, the skin friction coefficient is increased by the inner cylinder rotation. The critical (bulk flow) Reynolds number $Re_c$ decreases as the rotational speed increases. Thus, the rotation of the inner cylinder promotes the onset of transition due to the excitation of Taylor vortices.