• Journal of the Korea Institute of Military Science and Technology
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• v.8 no.3 s.22
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• pp.116-123
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• 2005

An experimental investigation on the static and dynamic stall characteristics of elliptic airfoil was performed by PIV velocity field measurements. The flow Reynolds number was $3.13{\times}10^5$ and the reduced frequency of the pitch oscillation ranged from 0.075 to 0.125. The onset of static stall was caused by boundary layer separation which started at the trailing edge and progressed toward the leading edge. However, dynamic stall was caused by the vortex shed at the leading edge region and the flow field showed a vortex dominated flow with turbulent separation and alternate vortex shedding. The increase of reduced frequency increased the dynamic stall angle of attack and intensified the flow hysteresis in the down-stroke phase.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.14 no.3
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• pp.51-59
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• 2006

The air purity-sterilizer was developed and the CFD and experimental studies were carried out in order to investigate the performance of a air purity-sterilizer. Overhaul and exchange efficiency were increased by the modularization of the air purity-sterilizer. The good performance was validated by the hot-wire measurements and flow simulations in the room. Mean velocities at the exit of the air purity-sterilizer were 0.91, 1.62, 1.99, and 6.14 m/sec according to the fan mode. And the flow visualization of pured air was shown by using CFD flow simulation in the room of 24, 50 pyeong. The results show that the air purity-sterilizer has a high performance enough to produce air purity-sterilizer on a commercial scale.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.138-138
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• 2022

Understanding a stream's or river's discharge is essential for a variety of hydrological and geomorphological applications at various sizes. However, depending on the stream environment and flow conditions, it is crucial to use the appropriate techniques and instruments. This will ensure that discharge estimations are as reliable as possible. This study presents developed smart system for continuous measurement of open channel discharge and evaluate streamflow measurement over various techniques. This includes developed smart flow meter as flow point measurements, smart water level sensor (installed on Hydraulic Structure ? Weir) and current meters. Advantages and disadvantages of each equipment are presented to ensure that the most appropriate method can be selected. we found that smart water level sensor is more prominent once used during flood event as compared to smart flow meter and current meters, while current meters seems to show better accuracy once applied for open channel.

• The KSFM Journal of Fluid Machinery
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• v.2 no.2 s.3
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• pp.19-26
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• 1999

Thermal output in a nuclear power plant is verified with calorimetric heat balance on the secondary plant. The calorimetry involves the precise measurement of the feedwater flow rate. However, the correct indication of feedwater flow rate obtained by a pressure-difference measurement across a venturi can be affected by instrument errors, fouling or a poorly developed velocity profile. This can result in an inaccurate mass flow rate and consequently an inaccurate estimate of power. The purpose of this study is to develop verification methods with accuracy better than $0.5\%$ for high precision flow measurement to be used for measuring feedwater flow rate. This chemical tracer method is a testing process that uses tracers which can be applied to quantify losses in electrical output due to the incorrect measurements of feedwater flow rate. And this system has good response to the variation of the flow rate. Accuracy of better than 0.5 percent can be expected for feedwater flow measurement, providing that the system can be stabilized during the test. This methodology is applicable to other flow systems well.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.311-317
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• 2005

Measurements of the leakage flow in the shrouded cavity were performed in axial compressor cascades at $Re=2.6{\times}10^5$. This paper describes the effects of the leakage flow tangential velocity on kinematics of the leakage flow in the shrouded cavity and consequent overall loss and exit flow turning at stator blade row downstream. Flow data and flow visualization images consistently indicate that leakage flow circumferentially migrates 2, 4 and 5 blade passages in the direction of rotation for ${\upsilon}_y/c=0.09$, 0.35 and 0.45, respectively where ${\upsilon}_y$ is the leakage tangential velocity and c is the mainstream velocity. The leakage flow contracts to a jet across the seal-tooth resulting in an increase in the leakage axial velocity-doubling the leakage axial velocity in upstream cavity compared to that in the downstream cavity. Consequently, two flow regions are distinguished before and after the seal-tooth. As increasing the leakage tangential velocity, the overall loss downstream of stator blade row decreases and the exit flow turning in the range of span. from the hub endwall to 15% increases while the decreases in the flow turning from 15% to 30% span is observed.

• Journal of Information Processing Systems
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• v.15 no.4
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• pp.820-832
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• 2019

Estimation of accurate blood volume flow in ultrasound Doppler blood flow spectrograms is extremely important for clinical diagnostic purposes. Blood volume flow measurements require the assessment of both the velocity distribution and the cross-sectional area of the vessel. Unfortunately, the existing volume flow estimation algorithms by ultrasound lack the velocity space distribution information in cross-sections of a vessel and have the problems of low accuracy and poor stability. In this paper, a new robust ultrasound volume flow estimation method based on multigate (RMG) is proposed and the multigate technology provides detail information on the local velocity distribution. In this method, an accurate double iterative flow velocity estimation algorithm (DIV) is used to estimate the mean velocity and it has been tested on in vivo data from carotid. The results from experiments indicate a mean standard deviation of less than 6% in flow velocities when estimated for a range of SNR levels. The RMG method is validated in a custom-designed experimental setup, Doppler phantom and imitation blood flow control system. In vitro experimental results show that the mean error of the RMG algorithm is 4.81%. Low errors in blood volume flow estimation make the prospect of using the RMG algorithm for real-time blood volume flow estimation possible.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.1
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• pp.54-62
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• 2009

The present study investigates the behaviour of overtopping flows falling on the leeside of a caisson breakwater with dissipating blocks through laboratory measurements. The falling overtopping flows in the leeside are expected to directly affect the leeside stability of the breakwater. This study focuses on not the resultant stability but the characteristic pattern of the overtopping flows depending on wave conditions through examining front velocity and plunging distance in the leeside. Regular waves were used to investigate the dependence of the overtopping flow pattern on wave conditions and a modified image velocimetry combining the shadowgraphy and cross-correlation method was employed for measurements of image and velocity. From the measurements, it is shown that the plunging distance and front velocity of the overtopping flow in the breakwater leeside increase as the wave period or height increases. From non-dimensional relationships between the variables, empirical formula for the velocity and overtopping distance are suggested.

• Journal of Mechanical Science and Technology
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• v.16 no.9
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• pp.1147-1155
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• 2002

Discharge flows from a centrifugal pump impeller with a specific speed of 150 [rpm, m$^3$/min, m] were experimentally investigated. A large axisymmetric collector instead of a volute casing was installed to obtain circumferentially uniform flow, i.e. without interaction of the impeller and the volute. The unsteady flow was measured at the impeller exit and vaneless diffuser using a hot film probe and a pressure transducer. The flow at impeller exit showed pronounced jet-wake flow patterns. The wake, which was on the suction/hub side at high flow rate, became enlarged pitchwisely on both the hub and the shroud side as the flow rate decreases. The pitchwise non-uniformity of the flow rapidly decreased along the downstream and the non-uniformity almost disappeared at radius ratio of 1.18 for medium flow rate. The mean vaneless diffuser flow was reasonably predicted using a one dimensional analysis when an empirical constant was used to specify the skin friction coefficient. The data can be used for a centrifugal pump impeller design and validation of CFD codes and flow modeling.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.5
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• pp.675-684
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• 2002

Two-dimensional, angle-resolved LDV(Laser Doppler Velocimetry) measurements of the turbulent rotating flow field in a confined cylinder have been performed. The configurations of interest are flows between a rotating upper disk with a rod attached by a disk or impeller($\theta$ = 45$^{\circ}$, 90$^{\circ}$) and a stationary lower disk in a confined cylinder. The mean flow velocity as well as the turbulent intensity of the flow field have been measured. The results show that the flow is strongly dependent on the position of the impellers or the disk, negligibly affected by the Reynolds number in turbulent flow. It is observed that the mixing effect of the axial flow impeller($\theta$ = 45$^{\circ}$) is better than that of the radial flow impeller($\theta$ = 90$^{\circ}$) or a disk.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.2
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• pp.1-8
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• 2002

The flow and combustion patterns have been investigated inside the gasoline engine cylinder with the swirl or tumble flow, whereas the air flow characteristics, which are generated in the part of intake system before entering into the intake manifold, have not been known completely. It is necessary to analyze the flow field in the intake system consisting of air rater, throttle valve and intake manifold. The throttle valve, used to control the intake air flow rate, is important because it makes various mass flow rate and flow patterns. Three-dimen-sional How characteristics such as velocities, turbulent intensities and Reynolds shear stresses are measured by the hot wire anemometer at the exit of the throttle valve with the variation in the valve opening angle($15^{\circ}$, $45^{\circ}$, $75^{\circ}$ and $90^{\circ}$) and the Reynolds numbers (45000, 70000 and 140000). There are a lot of changes in flow characteristics at $75^{\circ}$ due to the large recirculation flow comparing with those of the other cases, and the streamwise velocity is especially enforced strongly below the valve shaft. The other component velocities are relatively large near the centerline parallel to the valve shaft. The effects of the Reynolds number on the flow field are not severe.