• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.3
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• pp.10-17
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• 2005

An experimental study was conducted at a Mach number of 2.0 to investigate the buzz suppression method on an axisymmetric, external compression supersonic inlet. The inlet model has a fixed geometry with no internal contraction. The inlet configuration was altered by changing the cowling. Results show that source of buzz has been related to the existence in the flow field of velocity discontinuity across a vortex sheet which originates from a shock intersection point. With external compression inlet, buzz can be suppressed by positioning the oblique shock slightly inside or outside of the cowl.

• Geotechnical Engineering
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• v.1 no.2
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• pp.67-74
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• 1985

A study is made on the determination of the total head distribution using the random walk theory within a confined flow system with complicated boundary conditions. Both nonhomogeniety and anisotropy of the aquifer are considered. The overlying on the aquifer may have sheet piles and the impervious boundary may be inclined. Use is made of the Monte Carlo simulation based on the random walk theory to determine the total head at a given Point. A computer program is developed for practical use. The proposed method was evaluated by comparing the results with those obtained by other method, i.e., the conventional flow net, the finite difference method, and the method of fragment. It is found that all the values are in reasonable agreement and the method is sufficiently accurate for practical use.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.10
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• pp.1399-1408
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• 2000

A 2-dimensional temperature field measurement technique using PLIF (Planar Laser Induced Fluorescence) was developed and it was applied to an axisymmetric buoyant jet. Rhodamine B was used as a fluorescent dye. Laser light sheet illuminated a two-dimensional cross section of the jet. The intensity variations of LIF signal from Rhodamine B molecules scattered by the laser light were captured with an optical filter and a CCD camera. The spatial variations of temperature field of buoyant jet were derived using the calibration data between the LIF signal and real temperature. The measured results show that the turbulent jet is more efficient in mixing compared to the transition and laminar jet flows. As the initial flow condition varies from laminar to turbulent flow, the entrainment from ambient fluid increases and temperature decay along the jet center axis becomes larger. In addition to the mean temperature field, the spatial distributions of temperature fluctuations were measured by the PLIF technique and the result shows the shear layer development from the jet nozzle exit.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.128-134
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• 2014

A Experimental study on frequency characteristics of the microphone array covered with Kevlar in closed test section wind tunnel. Microphones that are flush mounted in a closed test section wall of wind tunnel are subject to very high flow noise resulting from the turbulence in the wall boundary layer. At this time the microphones measure the strong hydrodynamic fluctuations generated by the flow. The phenomena are referred to a microphone self-noise and a method for reducing this has studied. In this paper the array that covered with acoustically transparent Kevlar sheet was designed and made to reduce the flow-induced self-noise. For the validation frequency characteristics of the Kevlar, the microphone array was installed on the wall and test was performed for white noise and sine wave of several frequencies using loudspeaker. In addition, the paper compared the signals as a tension of Kevlar. The results were presented that tend to decrease the sound pressure level at high frequency above 3500Hz according to existence of Kevlar.

• Journal of the Korean Society of Combustion
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• v.1 no.1
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• pp.65-73
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• 1996

Flame propagation in a four-valve spark-ignition optical engine was visualized under lean-bum conditions with A/F=18 at 2000rpm. The early flame development in a four-valve pentroof-chamber single-cylinder engine was examined with imaging of the laser-induced Mie scattered light using an image-intensified CCD camera. Flame profiles along the line-of-sight were also visualized through a quartz piston window. Two-dimensional flame structures were visualized with a Proxitronic HF-1 fast motion camera system by Mie scattering from titanium dioxide particles along a planar laser sheet generated by a copper vapor laser. The flame propagation images were subsequently analysed with an image processing programme to obtain information about the flame structure under different tumble flow conditions generated by sleeved and non-sleeved intake ports. This allowed enhancement of the flame images and calculation of the enflamed area, and the displacement of its center, as a function of the tumble flow induced by the pentroof-chamber in the vicinity of spark plug. Image processing of the early flame development quantified the correlation between flame and flow characteristics near the spark plug at the time of ignition which has been known to be one of the most important factors in cyclic combustion variations in lean-burn engines. The results were also compared with direct flame images obtained from the natural flame luminosity of the lean mixture.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.285-288
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• 2009

In order to understand spray characteristics with inflowing air from the compressor in the APU gas turbine combustor, we performed spray visualization test by using ND-Yag Laser sheet beam. The sector combustor which size is 1/6 of the real combustor was manufactured. Turbo blower is used as an air supplying device to simulate gas turbine air flow condition. In the case of 75 m/s combustor inlet air flow condition, spray angle way increased and dispersed widely than without airflow condition.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.4 no.4
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• pp.39-47
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• 2005

In this paper, a novel high power micropump using active check valves in place of conventional passive check valves employed at the inlet and outlet ports is presented. It actively controls open/close motion of check valves using piezoelectric actuator for expansion/contraction of pump chamber. A prototype micropump having an effective size of $17mm{\times}8mm{\times}11mm$ is fabricated. Frequency-dependent flow rate characteristics, bi-directional flow characteristics and load characteristics are experimentally investigated using a timing control method for valve closing motion. From the obtained experimental results, it is ascertained that optimal values of the phase shift compared to the voltage to drive pump chamber are $15^{\circ}$ for inlet check valve and $195^{\circ}$ for outlet. Based on the obtained results, a sheet-type active shuttle valve that has a unified valve-body for inlet and outlet check valves is proposed. A micropump with an effective size of $10mm{\times}10mm{\times}10mm$ is fabricated and the basic characteristics are experimentally investigated.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.117-120
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• 2008

Numerical simulations and experiment of a hydrodynamic and thermally developed turbulent flow through square ducts (3.0 ${\times}$ 3.0 cm) with twisted tape inserts and with twisted tape inserts plus interrupted ribs are conducted to investigate regionally averaged heat transfer and friction factors. Turbulent swirl flows having Reynolds numbers ranging from 8,900 to 29,000, a rib height-to-channel hydraulic diameter(e/D$_h$) of 0.067, and a length-to-hydraulic diameter(L/D$_h$) of 30, are considered. The square ribs are arranged to follow the trace of the twisted tape and along the flow direction defined as axial interrupted ribs. The twisted tape has 0.1 mm thick carbon steel sheet with diameter of 2.8 cm, length of 90 cm, and 2.5 turns. Each wall is composed of isolated aluminum sections, and two cases of surface heating are set. The results show that uneven surface heating enhances the heat transfer coefficient over uniform heating conditions, and square ducts with twisted tape inserts plus interrupted ribs produces the best overall transfer performance.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.11
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• pp.1533-1537
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• 2014

$WO_3/Ag/WO_3$ multilayer was researched by using RF magnetron sputtering with transparent electrode. Process gas flow ratio with $Ar/O_2$ were selected the optimum conditions at 70sccm/2sccm and $WO_3$ thin film at its conditions was appeared at transmittance about 80% in the visible light region to the average. $WO_3/Ag/WO_3$ multilayer thin films were fabricated from the same process condition which was the same gas flow ratio of Ar and $O_2$ $WO_3/Ag/WO_3$ thin films were appeared transmittance about 93% and sheet resistance about $6.41{\Omega}/{\square}$. From the SEM images, each thin films were appeared when $WO_3$ is 40nm and $O_2$ is 10nm.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.21 no.1
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• pp.45-50
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• 2013

In this study, lumped-vortex element method and thin airfoil theory were used to analyze aerodynamic characteristics of airfoils with relative motion that had camber lines of NACA $44{\times}{\times}$ airfoil in 2-dimensional unsteady incompressible potential flow. Velocity disturbance due to airfoil was calculated by lumped-vortex element model and force distribution on airfoil by unsteady Bernoulli's equation. Variables in relative motion were considered the period p, the amplitude of flapping $A_f$ and pitching $A_p$, and the phase difference between flapping and pitching ${\phi}_p$ and the angle of attack ${\alpha}$. Due to movement of an airfoil, dag was induced in 2-dimensional unsteady incompressible potential flow. The numerical results show that the aerodynamic characteristics of the airfoil with flapping and pitching at the same time are illustrated. Especially the mean lift coefficient became smaller, but drag coefficient became larger.