• Journal of the Society of Naval Architects of Korea
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• v.32 no.1
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• pp.83-93
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• 1995

A numerical and experimental investigation on the flow characteristics in the rectangular duct of an MHD propulsion system has been carried out. In numerical analysis, three-dimensional, steady-state, viscous, incompressible electrically conducting fluid flow under the influence of uniformly applied magnetic and electric fields was treated using a finite-difference technique. It was found from the numerical study that when the Lorentz force is weak, the typical parabolic velocity profile under a laminar flow condition changes to an M shaped profile near the electrode region and that the pressure increases linearly from the inlet toward the outlet of the MHD duct under constant electro-magnetic field. In experiment, thrust of the MHD propulsion system can be controlled easily by varying electrode current. The measured pressure gradient along the MHD duct is proportional to the Lorentz force, which is in agreement with the numerical results.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.3
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• pp.360-368
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• 2010

A SCR catalytic filter system is used for reducing $NO_x$ and soot emissions simultaneously from diesel combustors. The amount of ammonia (as a reducing agent) must be controlled with the amount of $NO_x$ to obtain an optimal $NO_x$ conversion. Hence, gas mixing between ammonia and exhaust gases is vital to ensure that the SCR catalyst is optimally used. If ammonia mass distribution is not uniform, slip potential will occur in rich concentration areas. At lean areas, on the other hand, the catalyst is not fully active. The better mixing is indicated by the higher uniformity of ammonia mass distribution which is necessary to be considered in SCR catalytic filter system. The ammonia mass distributions are depended on the flow field of fluids. In this study, the velocity field of gaseous flow is investigated to characterize the transport of ammonia in SCR catalytic filter system. The influence of different injection placements on the ammonia mass distribution is also discussed. The results show that the ammonia mass distribution is more uniform for the injector directed radially perpendicular to the main flow of inlet at the gravitational direction than that at the side wall for both laminar (Re = 640) and turbulent flows (Re = 4255). It is also found that the mixing index decreases as increasing the heating temperature in the case of ammonia injected at the side wall.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.5
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• pp.567-576
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• 1999

An experimental study has been conducted to investigate the effects of the free stream turbulence intensity and Reynolds number on the heat transfer and flow characteristics In the linear turbine cascade. Profiles of the time-averaged velocity, turbulence intensity, and Reynolds stress were measured in the turbine cascade passage. The static pressure and heat transfer distributions on the blade suction and pressure surfaces were also measured. The experiments were made for the Reynolds number based on the chord length, Rec = $2.2{\times}10^4$ to $1.1{\times}10^5$ and the free stream turbulence intensity, $FSTI_1$ = 0.6% to 9.1 %. The uniform heat flux boundary condition on the blade surface was created using the gold film Intrex and the surface temperature was measured by liquid crystal, while hot wire probes were used for the flow measurements. The results show that the free stream turbulence promotes the boundary layer development and delays the flow separation point on the suction surface. It was found that the boundary layer flows on the suction surface for all Reynolds numbers tested with $FSTI_1$ = 0.6% are laminar. It was also found that the heat transfer coefficient on the blade surface increases as the free stream turbulence intensity increases and the flow separation point moves downstream with an increasing Reynolds number. The results of skin friction coefficients are in good agreement with the heat transfer results in that for $FSTI_1{\geq}2.6%$, the turbulent boundary layer separation occurs.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.4
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• pp.221-226
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• 2016

Since arterial disease in the upper extremity is less common than that in the lower extremity, experimental and numerical investigations related to upper extremity have been rarely performed. We created a three-dimensional model of the arteries, larger than approximately 1 mm, in a Korean adult's left hand (from brachial to digital arteries), from 3T magnetic resonance imaging (MRI) data. For the first time, a three-dimensional computational fluid dynamic method was employed to investigate blood flow velocity, blood pressure variation, and wall shear stress (WSS) on this complicated artery system. Investigations were done on physiological blood flows near the branches of radial and deep palmar arch arteries, and ulnar and superficial palmar arch arteries. The flow is assumed to be laminar and the fluid is assumed to be Newtonian, with density and viscosity properties of plasma.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.11
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• pp.999-1007
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• 2013

The present work reports numerical results of the pressure drop and heat transfer characteristics of pipes with various shapes such as circular, elliptical, circumferential wavy and twisted using a three-dimensional simulation. Numerical simulations are calculated for laminar to turbulent flows. The fully developed flow in pipes was modeled using steady incompressible Reynolds-averaged Navier-Stokes (RANS) equations. The friction and Colburn factor of each pipe are compared with those of a circular tube. The overall flow and heat transfer calculations are evaluated by the volume and area goodness factor. Finally, the objective of the investigation is to find a pipe shape that decreases the pressure loss and increases the heat transfer coefficient.

• The Journal of the Petrological Society of Korea
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• v.19 no.1
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• pp.51-65
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• 2010

The Dongmakgol Tuff is a stratigraphic unit which is composed of voluminous ignimbrites in the Cheolwon basin. The ignimbrites belong to pumice-rich vitric tuffs that show eutaxitic to parataxitic fabrics from fiamme or pumice clasts. They are almost densely welded and strongly flattened, but often parallel aligned and stretched. Also they exhibit flow indicators such as flow lineations, imbrications, tensional cracks and boudins from their alignment and/or elongation, and lithic and pumice clasts show lateral grading in their average maximum diameter. Flow direction map from the lineations, asymmetric structures and lateral grading diagram indicate that the Dongmakgol Tuff has a source from its southwestern part near a boundary between southern Dongmakri and northern Gomunri, and is considered that the ignimbrites took emplacement processes of laminar flows during the final stage of flowage and the flow lineations are from the result of shear stress during that times.

• Journal of Welding and Joining
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• v.26 no.4
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• pp.85-91
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• 2008

The grooving corrosion is caused mainly by the different microstructures between the matrix and weld which is formed during the rapid heating and cooling cycle in welding. By this localized corrosion reaction of pipes, it evolves economic problems such as the early damage of industrial facilities and pipe lines of apartment, and water pollution. So lots of researches were carried out already about grooving corrosion mechanism of ERW carbon steel pipe but there is seldom study for water hammer happened by fluid phenomenon and corrosion rate by flow velocity. In this study, the analysis based on hydrodynamic and fracture mechanics was carried out. ANSYS, FLUENT and STAR-CD were used for confirmation of flow phenomenon and stress on the pipe. As the results, fatigue failure is able to be happened by water hammer and grooving corrosion rate is increased cause by turbulent. Grooving corrosion is happened on the pipe, then friction loss of fluid is occurred from corroded part. Erosion can be happened enough in corroded region of microscopic size that wear "V" form. Also pipe is able to be damaged by water hammer effects because of corroded region is general acting as a notch effects. Corrosion depth was more than half of total thickness, it can be damaged from water hammer pressure.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.3
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• pp.725-733
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• 1990

An analysis of laminar mixed convection flow adjacent to the inclined flat surface which is subjected to a uniform temperature in a uniform free stream is performed. Nonsimilar boundary layed equation are derived by using the mixed convection parameters such that smooth transition from the purely forced convection limit to the purely free convection limit is possible. The governing equations are solved by a finite difference method using the coupled box scheme of sixth order. Numerical results are presented for prandtl numbers of 0.7 and 7 with the angle of inclination ranging from 0 to 90 degree from the vertical. The velocity distributions for the buoyancy assisting flow exhibit a significant overshoot above the free stream value in the region of intense mixed convection and the velocity field is found to be more sensitive to the buoyancy effect than the temperature field. The separation point near the wall was obtained for the buoyancy opposing flow. The local Nusselt number increases for buoyancy assisting flow and decreases for opposing flow with increasing value of the local Grashoff number in the mixed convection parameter. For large Prandtl number, the Nusselt number and the friction factor decrease significantly near the separation point. Present numerical predictions are in good agreement with recent experimental results by Ramachandran.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.2
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• pp.98-111
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• 1993

Two-dimensional nonlinear free-surface wave problems are analyzed with consideration of viscosity. Navier-Stokes equation and continuity equation are solved by the application of Finite Analytic Method, and MAC scheme is used far the treatment of free surface. Surface tension effect is also considered and laminar flow is assumed. The free-surface waves in shallow water, the flows around a vortex-pair with free surface and the wave ahead of a rectangular body are simulated to test the present numerical scheme. In the shallow water problem, viscous effect due to the friction on the bottom is observed. In the second problem, the approach of a vortex-pair to the free surface is simulated to examine the interaction of vortex-pair with the free surface. In the third problem, the wave ahead of a semi-infinite floating body is simulated.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.2 no.1
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• pp.37-48
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• 1990

The drag and heat transfer reduction phenomena and degradation effects of drag reducing polymer solutions which are known as the viscoelastic fluids are investigated experimentally for the turbulent circular tube flows. Two stainless steel tubes are used for the experimental flow loops. Aqueous solutions of Polyacrylamide Separan AP-273 with concentrations from 300 to 1000 wppm are used as working fluids. Flow loops are set up to measure the friction factors and heat transfer coefficients of test tubes in the once-through system and the recirculating flow system. Test tubes are heated by power supply directly to apply constant heat flux boundary conditions on the wall. Capillary tube viscometer and falling ball viscometer are used to measure the viscous characteristics of fluids and the characteristic relaxation time of a fluid is determined by the Powell-Eyring model. The order of magnidude of the thermal entrance length of a drag reducing polymer solution is close to the order of magnitude of the laminar entrance length of Newtonian fluids. Dimensionless heat transfer coefficients of the viscoelastic non-Newtonian fluids may be represented as a function of flow behavior index n and newly defined viscoelastic Graetz number. As degradation continues viscosity and the characteristic relaxation time of the testing fluids decrease and heat transfer coefficients increase. The characteristic relaxation time is used to define the Weissenberg number and variations of friction factors and heat transfer coefficients due to degradation are presented in terms of the Weissenberg number.