• Journal of Mechanical Science and Technology
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• v.15 no.12
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• pp.1784-1793
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• 2001

The flow fields around an elliptic cylinder of axis ratio AR=2 adjacent to a free surface were investigated experimentally using a water channel. The main objective is to understand the effect of the free surface on the flow structure in the near-wake. The flow fields were measured by varying the depth of cylinder submergence, for each experimental condition, 350 velocity fields were measured using a single-frame PIV system and ensemble-averaged to obtain the spatial distribution of turbulent statics. For small submergence depths a large-scale eddy structure was observed in the near-wake, causing a reverse flow near the free surface, downstream of the cylinder. As the depth of cylinder submergence was increased, the flow speed in the gap region between the upper surface of the cylinder and the free surface increased and formed a substantial jet flow. The general flow structure of the elliptic cylinder is similar to previous results for a circular cylinder submerged near to a free surface. However, the width of the wake and the angle of downward deflection of the shear layer developed from the lower surface of the elliptic cylinder are smaller tan those for a circular cylinder.

• Journal of Advanced Marine Engineering and Technology
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• v.18 no.1
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• pp.81-91
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• 1994

Combustion noise involved with chemical heat release and turbulent process in turbopropulsion systems, gasturbine, industrial furnaces and internal engines is indeed noisy. The experimental study reported in this paper is made to identify a dominant combustion noise in jet flames. Gaseous propane and kerosene fuel have been used with air as the oxidizer in a different jet combustion systems. Combustion and aerodynamic noise are studied through far field sound pressure measurements in an anechoic chamber. And also mean temperature and velocities and turbulent intensities of both isothermal and reacting flow fields were measured. It is shown that axial mean velocity of reacting flow fields is higher about 1 to 3m/sec than that of cold flow in a gaseous combustor. As the gaseous fuel flow rate increases, the acoustic power increases. But the sound pressure level for the spray flame decreases with increasing equivalence ratio. The influence of temperature in the combustion fields due to chemical heat release has been observed to be a dominant noise source in the spray flame. The spectra of combustion noise in gaseous propane and kerosene jet flame show a predominantly low frequency and a broadband nature as compared with the noise characteristics in an isothermal air jet.

• Journal of Electrical Engineering and Technology
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• v.5 no.2
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• pp.329-336
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• 2010

The paper describes the electrical and optical properties of underwater discharges in highly inhomogeneous electric fields caused by 1.2/50 ${\mu}s$ impulse voltages as functions of the polarity and amplitude of the applied voltage, and various water conductivities. The electric fields are formed by a point-to-plane electrode system. The formation of air bubbles is associated with a thermal process of the water located at the tip of the needle electrode, and streamer coronas can be initiated in the air bubbles and propagated through the test gap with stepped leaders. The fastest streamer channel experiences the final jump across the test gap. The negative streamer channels not only have more branches but are also more widely spread out than the positive streamer channels. The propagation velocity of the positive streamer is much faster than that of the negative one and, in fact, both these velocities are independent of the water conductivity; in addition the time-lag to breakdown is insensitive to water conductivity. The higher the water conductivity the larger the pre-breakdown energy, therefore, the ionic currents do not contribute to the initiation and propagation of the underwater discharges in the test conditions considered.

• Journal of Magnetics
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• v.11 no.2
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• pp.74-76
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• 2006

Dynamic behaviors of transverse domain walls (TDWs) in rectangular shaped thin-film magnetic nanowires with different widths under applied magnetic fields less than the Walker field were studied by micromagnetic simulations. It was found that the velocity of stable TDWs in the viscous region increases from 147 to 419 m/s and their mass decreases from $6.24{\times}10^{-23}\;to\;2.70{\times}10^{-23}kg$ with increasing strength of the applied magnetic field ranging from 5 to 20 Oe for the nanowire with a dimension of 10 nm in thickness and $5{\mu}m$ in length, and 50 nm in width. With increasing the width of nanowires from 50 to 125 nm at a specific field strength of 5 Oe, the TDW's velocity also increases from 147 to 246 m/s and its mass decreases from $6.24{\times}10^{-23}\;to\;5.91{\times}10^{-23}kg$.

• 한국연소학회:학술대회논문집
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• 2004.11a
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• pp.70-75
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• 2004

The effect of electric fields on the stability of non-premixed laminar lifted flame in coflow jets has been investigated by applying high voltage alternative current (AC) to the nozzle of propane fuel. The stable lifted flame which exist in far field of jets, the liftoff height was not effected by applied voltage. This implies that the cold jet between the nozzle and flame base can be analyzed with the previous cold jet theory. Flame liftoff and reattachment velocities were also measured as function of applied voltage and frequency. The fuel jet velocity at flame liftoff and reattachment increased with increasing voltage, implying that the range of flame srability can be extended with the AC charging. However the liftoff velocity increased with frequency of AC charging on nozzle, whereas the reattachment velocity decreases with frequency. The liftoff and reattachment velocities were correlated linearly with voltage considering the effects of frequency.

• Journal of Ocean Engineering and Technology
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• v.26 no.3
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• pp.61-65
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• 2012

Air-water flow measurements are of importance for the coastal and ocean engineering fields. Although kinematic investigations of the multi-phase flows have been conducted for long time, velocity measurements still are concerned with many researchers and engineers in coastal and ocean areas. In the present study, an imaging technique using shadowgraphy and fiber optic probe for velocity measurements of air bubbles is introduced. The shadow graphy image technique is modified from the typical image velocimetry methods, and optical fibers are used for the well-known intrusive coupled phase-detection probe system. Since the imaging technique is a non-intrusive optical method from the air, it is usually applied for 2D flows. On the other hand, the double fiber optic probes touch flows regardless of flow patterns. The results of the flow measurements by both methods are compared and discussed. The methods are also applied to the measurements of overtopping flows by a breaking wave over the structure fixed on the free surface.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.690-695
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• 2001

The three-dimensional spatial structures of impeller flow created by a six bladed Rushton turbine have identified based on the volumetric velocity information from multi-plane stereoscopic PIV measurements. A total of 10 planes with 2 mm space with a 50 mm by 64 mm size of the field of view were targeted. To reduce the depth of focus, we adopted an angle offset configuration which satisfied the Scheimpflug condition. The distortion compensation procedure was utilized during the in situ calibration. Phase-locked instantaneous data were ensemble averaged and interpolated in order to obtain mean 3-D, volumetric velocity fields on a 60 degree sector of a cylindrical ring volume enclosing the turbine blade. Using the equi-vorticity surface rendering, the spatial structure of the trailing vortices was clearly demonstrated. Detail flow characteristics of the radial jet reported in previous studies of mixer flows were easily identified.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.9
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• pp.698-706
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• 2006

Experiment and numerical calculation have been peformed to investigate mixed convection heat transfer between inclined parallel plates. Particle image velocimetry (PIV) with thermo-sensitive liquid crystal (TLC) tracers is used for visualizing and analysis. This method allows simultaneous measurement of velocity and temperature fields at a given instant of time. Quantitative data of the temperature and velocity are obtained by applying the color-image processing to a visualized image, and neural network is applied to the color-to-temperature calibration. The governing equations are discretized using the finite volume method. The results are presented for the Reynolds number ranges from 0.004 to 0.062, the angle of inclination, ${\Theta}$, from 0 to 45 degree and Prandtl number of the high viscosity fluid is 909. The results show velocity, temperature and mean Nusselt numbers distributions. It is found that the periodic flow of mixed convection between inclined parallel plates is shown at $0^{\circ}{\leq}{\Theta}<30^{\circ}$, Re<0.062, and the flow pattern can be classified into three patterns which depend on Reynolds number and the angle of inclination. The minimum Nusselt numbers occur at Re=0.05 regardless of the angle of inclination.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.4 s.175
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• pp.839-847
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• 2000

This paper presents modal analysis and mean conveying velocity (M.C.V.) control of bowl parts feeder activated by piezoactuators. Bowl parts feeders are being widely used in many industry fields for automatic assembly line. In general, the electromagnet has been and being used as exciting actuator of these vibratory bowl feeders. However, because of complexity of its mechanism and limited capability of the electromagnet actuator, there exist various impending problems such as severe noise, nonlinear motion of parts, passive characteristics and so forth. As one of solutions for these problems, piezoelectric actuators as new actuating technology have been proposed recently to excite the bowl parts feeder. In this paper, modal analysis of the proposed model has been performed to examine the modal characteristics of the model by using commercial FEM software and modeling with respects to MCV is constructed. Finally, MCV of the parts is to be controlled to track the desired one with PID controller.

• Journal of the Korean Society of Visualization
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• v.12 no.1
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• pp.35-42
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• 2014

Magnetic resonance velocimetry (MRV) is a versatile flow visualization technique using magnetic resonance imaging machine developed for the medical purpose. Recently, MRV is often utilized to analyze engineering flows due to its superior features of MRV such as capabilities of measuring flows with complicated, opaque flow geometry unlike optical techniques, 3-dimensional volumetric velocity vectors within a few hours, and etc. The purpose of this study was to validate the MRV data and evaluate the accuracy of the mean velocity profiles that we acquired for a turbulent flow in a circular pipe using a MR machine installed in Korea Basic Science Institute, Ochang, Korea. In addition, we briefly describe a procedure of parameter optimization for the operation of MRV. The results indicate that the MRV measurements provided well resolved mean velocity fields with a quite reasonable accuracy according to the inner and outer layer scaling laws of the turbulent pipe flows.