• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.571-574
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• 2010

Large-eddy simulation has been conducted to simulate turbulent boundary-layer flows over an array of regularly distributed obstacles considering various cases of a wind incident angle. The effect of wind direction was investigated in the square cube array that periodic boundary condition was imposed. Characteristics of the turbulent flow over the obstacle array have been found to be very sensitive to the direction of prevailing wind or of mean wind or of mean pressure gradient but varied with height, specially below the urban canopy. Turbulent statistics are changed sensitively with the direction of mean pressure gradient around 10 degree.

• The KSFM Journal of Fluid Machinery
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• v.4 no.2 s.11
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• pp.29-34
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• 2001

Experimental and numerical studies are conducted to investigate the flow field over a NACA0012 airfoil with ground effects. In experiment, the ground is simulated by a moving belt system. From the comparison between the experimental and numerical results, it is concluded that the velocity gradient over the ground plane causes the increments in pressure coefficient on lower surface of the airfoil and reduces the suction peak at the leading edge.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.2023-2028
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• 2004

The effects of nozzle-lip thickness on the relationship between screech tone and broadband shock-associated noise were experimentally investigated using a convergent-divergent nozzle with a design Mach number of 2.0. Overall sound pressure levels (OASPL) and noise spectra were obtained at far-field locations. Schlieren optical system was used to visualize the flow-fields of supersonic jets. A baffle plate was installed at the exit of the nozzle and its size was varied to obtain different nozzle-lip thicknesses. Experiment was carried out over a wide range of nozzle pressure ratios from 2.0 and 18.0, which corresponds to over- and under-expanded conditions. The results obtained clearly show that the screech tones are influenced by the nozzle-lip thickness. It is found that the screech tone and its peak amplitude are strongly dependent on whether the jet is over-expanded and under-expanded at the nozzle exit.

• Journal of the Korea Institute of Military Science and Technology
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• v.5 no.2
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• pp.83-90
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• 2002

An experimental study was conducted to investigate the effects of a leading edge extension(LEX) on the vortex flow field over a delta wing by measuring the total pressure distribution in a subsonic wind tunnel. Freestream velocity was 40m/sec and Reynolds number per meter was $1.76{\times}10^6$. The wing with the LEX experienced a strong interaction between the LEX and wing vortices. As the angle of attack increased, the coupled vortex field of these two vortices maintained its strength and concentricity much better than the vortex field over the wing without the LEX.

• Journal of ILASS-Korea
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• v.20 no.2
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• pp.82-87
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• 2015

A nozzle with vortex generator was used to develop the low pressure nozzle with high atomization performance and the nozzle atomized the liquid by centrifugal shear forces. In order to analyze the atomization characteristics, a shadowgraphy method was used and the measurement of droplet size was performed by using laser diffraction analyzer. The liquid injection pressure was fixed as 0.03 bar which is very low pressure and the gas injection pressures were changed from 0 bar to 2.0 bar. As a result, the breakup was achieved at the air injection pressure of 0.25 bar and over. The nozzle with the orifice diameter of 0.4 mm and the orifice gap of 0.25 mm presented small droplet diameters under 50 at the air injection pressure of 0.75 bar.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.196-201
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• 2004

Adhesive joints have been widely used for fastening thin adherends because they can distribute the load over a larger area than mechanical joints, require no hole, add very little weight to the structure and have superior fatigue resistance. However, the fatigue characteristics of adhesive joints are much affected by applied pressure during curing operation because actual curing temperature is changed by applied pressure and the adhesion characteristics of adhesives are very sensitive to manufacturing conditions. In this study, cure monitoring and torsional fatigue tests of adhesive joints with an epoxy adhesive were performed in order to investigate the effects of the applied pressure during curing operation. From the experiments, it was found that the actual curing temperature increased as the applied pressure increased, which increased residual thermal stress in the adhesive layer. Therefore, the fatigue life decreased as the applied pressure increased because the mean stress during fatigue tests increased due to the residual thermal stress.

• Journal of Mechanical Science and Technology
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• v.18 no.6
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• pp.1036-1041
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• 2004

A newly designed pressure-scanning slit viscometer is developed to combine an optical device without refraction while measuring blood viscosity over a range of shear rates. The capillary tube in a previously designed capillary viscometer was replaced with a transparent slit, which is affordable to mount optical measurement of flowing blood cells. Using a pressure transducer, we measured the change of pressure in a collecting chamber with respect to the time, p(t), from which the viscosity and shear rate were mathematically calculated. For water, standard oil and whole blood, excellent agreement was found between the results from the pressure-scanning slit viscometer and those from a commercially available rotating viscometer. This new viscometer overcomes the drawbacks of the previously designed capillary viscometer in the measuring whole blood viscosity. First, the pressure-scanning slit viscometer can combine an optical instrument such as a microscope. Second, this design is low cost and simple (i.e., ease of operation, no moving parts, and disposable).

• 한국가시화정보학회:학술대회논문집
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• 2004.11a
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• pp.10-13
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• 2004

The PSP(pressure sensitive paint) technique has recently received a large attention as a new revolutionary optical method to measure absolute pressure distribution on a model surface. The PSP technique can be applied to quantitatively investigate flow structure using a CCD camera and image processing technique. In the static calibration, the luminescent intensity of PSP coatings was measured from 0kPa to 11kPa with 0.5, 1, 2kPa increments. In this study, the low-pressure PSP technique was applied to an oblique impinging jet to measure pressure field variations on the impingement plate with varying angle of an oblique jet. The flow structure over the impingement plate was visualized using a surface tracing method. As a result, the detail pressure field distributions of the oblique low-speed impinging jet were visualized effectively using the PSP technique.

• Tribology and Lubricants
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• v.4 no.1
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• pp.69-73
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• 1988

The effects of journal speed and bearing load on pressure distribution and the temperature distribution of bearing surface are investigated experimentally. The journal bearing which has 219.94mm diameter, length-to-diameter ratio of L/D=0.8 and clearance ratio of 0.004 is used. Journal has a built-in pressure transducer for the measurement of pressure distribution in the mid plane of bearing. Bearing surface temperatures are measured at 60 points. The bearing load is varied from 300 N to 5900 N and journal speed from 300 rpm to 2500 rpm. As the load is increased under constant speed, the location of maximum pressure moves to the site of minimum film thickness, and maximum pressure and absolute value of minimum pressure are increased. The temperature distribution in vicinity of oil inlet shows that heated lubricant's carry-over exists around the oil inlet.

• Journal of the Korean Ceramic Society
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• v.30 no.4
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• pp.309-315
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• 1993

Gas pressure sintering is a promising process in various densification methods of high strength Si3N4 ceramics. Environmental influences on gas pressure sintering of Si3N4 was investigated with the variationof packing powder, specimen container and N2 gas pressure. The specimens had higher density, larger weight loss and inhomogeneous color in graphite specimen container than in SN26 crucible. The variations of sintering densities in various packing powders (Si3N4, SN26, AlN, BN) were very small but SiC powder was synthesised in graphite crucible with Si3N4 packing powder, aluminium oxynitride compounds were synthesised in SN26 crucible with AlN packing power. Also N2 gas pressure over 20kg/$\textrm{cm}^2$ reduced the densification of Si3N4 in one step-gas pressure sintering. As the result of two step-gas pressure sintering at 700kg/$\textrm{cm}^2$ for 15min., relative density of 99.9% and 3-point bending strength of 1090MPa and dense microstructure of 3~4${\mu}{\textrm}{m}$ grain size were obtained.