• Journal of the korean Society of Automotive Engineers
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• v.15 no.3
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• pp.81-88
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• 1993

This report describes the experimental research on the flow phenomena of the aq uaous polymer solution within the Cuette flow of the concentric, cylinders type with a wide circular gap. We have investigated the phenomena of the fluid flow through torque measuring in the system that the inner cylinder is stationary and the outer one is rotating. Geometrical parameters of the system are the gap ratio of t/R$_{0}$=0.2 and Aspect ratio of l/t=100. The torque increases considerably in about 420-480RPM, So, it is considered a turbulent transition boundary, the higher plymer concentration is, the lower torque value is and the higher transition Reynolds number is. In each of the polymer concentration, the unstable boundary of torque, that is, idiosyncrasies of torque is observed around 220-280RPM. and the boundary is looked upon as a resonant vibration which is caused by the inner cylinder and tortional vibration of torque sensor.r.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.5
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• pp.637-645
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• 1999

Horizontal two-phase flow pressure drop within rectangular channels with small gap heights have been examined experimentally. The gap heights range from 0.4mm to 4mm corresponding to aspect ratios(the channel height divided by the width) from 0.02 to 0.2. Water and air were used as the test fluids with the superficial velocity ranges being 0.03-2.39m/s and 0.05-18.7m/s, respectively. The experimental results In rectangular channels were compared with the Lockhart-Martinelli correlation, which are widely used for conventional round tube. The Lockhart-Martinelli correlation turned out to be Inappropriate to represent the present experimental data. In this respect, considering the aspect ratio and gap-height effects, an empirical correlation on two-phase flow pressure drop was proposed. The proposed correlation successfully covers the bubbly, plug, slug and annular flow regimes.

• Tribology and Lubricants
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• v.33 no.3
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• pp.85-91
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• 2017

This work studies the flow behaviors in the gap between the friction pad and separator in wet-clutch systems. The fluid volume of the lubricant is modeled using the entire system of wet-clutch pack of a dual clutch transmission that has larger outer radius of odd gear shifts and smaller inner radius of even gear shifts. Flow behaviors in the gap of the clutch pad are computed using the gear shift modes that consider the real relative velocities between the friction pad and separator. Flow behaviors in the gap of the disengaged clutch pad are mainly investigated for the wet-clutch system, whereas the engaged clutch pad is modeled with no fluid rate through the contacting surfaces. The developed hydrodynamic fluid pressures and velocity fields in the clutch pad gap are computed to obtain the relevant information for managing flow rates in wet-clutch packs under dual operating conditions during gear shifts. These hydrodynamic pressures and velocity fields are compared on the basis of each gear level and gap location, which is necessary to determine the effects of groove patterns on the friction pad. Shear stresses in the gap locations are also computed on the basis of the gear level for the inner and outer clutch pads. The computed results are compared and used for the design of cooling capacity against frictional heat generation in wet-clutch pack systems.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.7
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• pp.585-595
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• 2011

The flow characteristics of synthetic jet depending on rectangular and circular jet exit configuration are investigated using numerical computation with cross flow. In rectangular slot, synthetic jet generates the strong vortex but supplies fewer momentum and effectiveness of flow control is reduced along flow direction. In circular slot, regular vortex is formed from slot center to end. It affects the wider region than rectangular slot. The distribution of wall shear stress is considered in order to indicate the effectiveness of flow control device for flow separation delay. Consequently, circular slot is a more suitable candidate for delaying flow separation. In order to derive the optimal shape of a circular slot exit, hole gap and diameter that affect the flow structure and flow control were analyzed. As a result, consider the hole diameter and gap of circular slot exit design, effectiveness of the flow control can be increased.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.2
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• pp.132-138
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• 2011

In the present article, we investigate numerically turbulent flow of air through compound rectangular channels. Large eddy simulation(LES) is employed for unsteady turbulence modeling. LES gives better predictions for the axial mean velocity distribution than those of other turbulent models. Strong large-scale quasi-periodic flow oscillations are observed in most of the geometries investigated. Such large-scale flow oscillations in compound rectangular channels are similar to the quasi-periodic flow pulsation through the gaps between fuel rod bundle in nuclear reactor. It exists in any longitudinal connecting gap between two flow channels. The frequency of this flow oscillation is determined by the geometry of the gap. The large scale cross motions through the rectangular compound channels induce significant heat transfer enhancement of the compound channel flow.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.795-800
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• 2000

A CCFL(Counter Current Flow Limit) test have been performed in narrow annular gaps with large diameter, because it has been confirmed that the CCFL phenomena affected the critical power in hemispherical narrow gap geometries from the SONATA(Simulation Of Naturally Arrested Thermal Attack)-IV (In-Vessel)/VISU(Visualization)-II experiments. The objectives of the CCFL experiments are to investigate the small gap sizes(1, 2mm) effect on CCFL under the large diameter condition and to confirm the findings of the VISU-II study that global dryout in hemispherical narrow gaps was induced by the CCFL. The test section was made of acrylic resin to allow visual observation on the two-phase flow behaviors inside annular gaps. It was observed from visualization that a part of water supplied was accumulated in the upper plenum and a significant increase in the differential pressure across the gap was occurred, which was the definition of the CCFL occurrence in this experimental study. From the experimental results in annular gap with large diameter it can be known that an increase in the differential pressure was not big at small air flow-rates. When the CCFL was occurred, the differential pressure across gaps was increased significantly and a water accumulated in the upper plenum. The occurrence of CCFL was correlated using the Wallis parameter.

• Journal of Mechanical Science and Technology
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• v.15 no.7
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• pp.941-950
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• 2001

A study of counter-current two-phase flow in narrow rectangular channels has been performed. Two-phase flow regimes were experimentally investigated in a 760mm long and 100mm wide test section with 2.0 and 5.0mm gap widths. The resulting flow regime maps were compared with the existing transition criteria. The experimental data and the transition criteria of the models showed relatively good agreement. However, the discrepancies between the experimental data and the model predictions of the flow regime transition become pronounced as the gap width increased. As the gap width increased the transition gas superficial velocities increased. The critical void fraction for the bubbly-to-slug transition was observed to be about 0.25. The two-phase distribution parameter for the slug flow was larger for the narrower channel. The uncertainties in the distribution parameter could lead to a disagreement in slug-to-churn transition between the experimental findings and the transition criteria. For the transition from churn to annular flow the effect of liquid superficial velocity was found to be insignificant.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1897-1902
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• 2003

An 1/21.6 scaled experimental facility was prepared utilizing the results of a scaling analysis to simulate the APRI400 reactor and insulation system. The behaviors of the boiling-induced two-phase natural circulation flow in the insulation gap were observed, and the liquid mass flow rates driven by natural circulation loop were measured by varying the wall heat flux, upper exit slot area and configuration. And non-heating experiments have also been performed and discussed to certify the hydraulic similarity of the heating experiments by injecting air equivalent to the steam generated in the heating experimental condition.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1863-1868
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• 2004

The present study concerns a computational study of fully developed laminar flow of a Newtonian fluid through an eccentric annulus with a combined bulk axial flow and inner cylinder rotation. This study considers the identical flow geometry as in the calculation of Escudier et $al.^{(3)}$ An unexpected feature of the calculations for eccentricity ${\varepsilon}$)0.7 is the appearance of a second peak in the axial velocity, located in the narrowing gap. The distribution of the axial component of the surface shear stress has a maximum in the narrowing gap and a minimum in the widening gap.

• Journal of computational fluids engineering
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• v.10 no.1
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• pp.73-79
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• 2005

Micro sensor is very useful for flow measurements in a number of engineering applications. Especially, it is necessary for the development of MEMS. This paper presents the 3D numerical simulation of flows around a micro flow sensor, which is mounted on a flat plate. The effects of the sensor configuration (i.e. bottom gap) and the Reynolds number on the flow field are numerically investigated. The numerical results indicate that the bottom gap clearly affects the flow fields over the top surface of the sensor. The Reynolds numbers also show a significant influence on the flow nature, especially on the recirculation zone at downstream of the sensor. The present results illustrate a certain improvement on the flow field for the sensor installed at O.5mm above the wall with four pillars, comparing with that directly mounted on the wall.