• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.10
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• pp.954-961
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• 2008

An experimental study has been conducted to investigate the flow field around the wing having a circular damage hole. The damage was represented by a circular hole passing through the model with 10% airfoil chord diameter and normal to the chord. The hole was centered at quarter or half chord. The PIV flow fields and static pressure measurements on the wing upper and lower surface were carried out at Rec=2.85×105 based on the chord length. The PIV results showed the two types of flow structures around a damage hole were formed. The first one was a weak jet that formed an attached wake behind the damage hole. The second one resulted from increased incidence; this was a strong jet where the flow through the hole penetrates into the free-stream resulting in extensive separation of oncoming boundary layer flow and development of a separated wake with reverse flow. The surface pressure data showed a big pressure alteration near the circular damage hole. The severity of pressure alteration was increased as a damage hole located nearer to the leading edge.

• Journal of the Korean Society of Marine Environment & Safety
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• v.17 no.1
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• pp.29-37
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• 2011

PIV measurements of the velocity field, pressure field, vorticity, and turbulent intensity in the rear of curved section of an oil fence with current speed showed that the flow directions in the rear of flow boundary area were similar to those in the front of it. As the current speed increased, the patterns of pressure distribution were changed, and the turbulent flow became more irregular. CFD simulations under the same conditions as the PIV tests showed that the flow patterns of the wake were similar to those by PIV tests in speed of 0.3 m/s and less, but were distinctively deviated from those in 0.4 m/s due to the flexibility of the oil fence, which was not properly taken care of in CFD modeling.

• Journal of the Korean Society for Marine Environment & Energy
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• v.9 no.2
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• pp.85-91
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• 2006

This study deals with the flow over a flat plate with repeated roughness elements of 2-dimensional rectangular shape, which can be applied into the study on the natural geographical roughness and the turbulent flow on roughened solid surface. Part 1 of the study showed that the ratio between the spacing and the height of roughness elements plays a crucial role in developing the flow pattern near wall surface. The present study complements the turbulence characteristics, the utilization of friction velocity as well as integral parameters. Results confirmed that k-type roughness(s/H=7 or 14) is certainly a more effective means than d-type roughness (s/H=3.5) in thickening the viscous region.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.6
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• pp.852-860
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• 1986

The effect of placing a worktable in a vertical laminar flow clean room is invesgiated by a numerical simulation. The model clean room is assumed to be a rectangular square of 2m*2m, in which a worktable of 0.8m long and 0.1m thick is located at 0.7m above the floor. Major parameters are the horizontal position of the table and the inlet flow velocity. The flow is assumed to be laminar throughout the clean room. Navier-Stokes equations with the pressure terms are directly solved by the SIMPLE algorithm. Boundary conditions at the two exits are given in terms of pressure conditions. The flow pattern, pressure loss due to viscous friction, the ratio of flow rates through each exit and pressure imbalance at the exits are calculated. All of the flow characteristics are seen to vary substantially with the location of the table, but are quite insensitive to the inlet flow velocity(Reynolds number). As an example, the flow rate through each exit can very by as much as 30% depending on the location of the table.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.3
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• pp.53-64
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• 2018

In this study, computational simulation was performed to investigate the characteristics of air/fuel mixing according to the shape of the injector exit when the transverse jet was injected into a supersonic flow. Non-reacting flow simulation was conducted with fixed mass flow rate and the same cross-sectional area. To validate the results, free stream Mach number and jet-to-crossflow memetum ratio are set to 3.38 and 1.4, respectively, which is same as the experimental condition. Further, separation region, structure of the under-expended jet, jet penetration height, and flammable region of hydrogen for five different injectors compared.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.3
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• pp.702-715
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• 1990

This paper describes behaviors of two-phase open channel flow inside the flash chamber of a horizontal Multi-Stage-Flash evaporator numerically along with the experimental observations. Bubble trajectories and the velocity and temperature distributions of the liquid phase were predicted by using the particle-source-in-cell(PSI-Cell) method with the appropriate bubble motion/growth equations. Size and number of bubble nuclei embedded in the incoming liquid(brine) were taken into account as important parameters in addition to the conventional ones such as the velocity, degree of inlet superheat, inlet opening height, and the liquid level. Bubble motions, which are unsteady, appeared to be mostly determined by the buoyancy and the drag forces. The calculations, though a number of simplifying assumptions were made, reasonably simulated the hydrodynamic behaviors of the two-phase horizontal stream observed in the experiments. The simulated temperature distributions also agreed fairly well with the other's measurements. Non-equilibrium allownaces, evaluated from the simulated temperature distributions, were within the range of those obtained from the existing correlations, and reduced with the increases of the number and size of incoming bubble nuclei due to vigorous flashing.

• KEPCO Journal on Electric Power and Energy
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• v.2 no.2
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• pp.211-221
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• 2016

The increase of world's population and economic development are the keys drivers behind growing demand for energy. Especially the demand for electricity would eventually result in an increase of coal usage. Therefore ultra supercritical circulating fluidized bed boiler has been developed as solutions of economic eco-friendly technologies for coal and of increasing supplies of low grade fuels. Ultra supercritical circulating fluidized bed boiler has an once through type of steam cycle different from drum type in subcritical circulating fluidized bed boiler. Also, the duplication of a proven commercial module with 100-300 MWe subcritical circulating fluidized bed might be the key for design of 500~800 MWe ultra supercritical circulating fluidized bed boiler. After 2017, ultra supercritical circulating fluidized bed boiler might become standard model over subcritical circulating fluidized bed boiler. Therefore, this paper will help you to understand ultra super critical circulating fluidized bed (USC-CFB) through describing the background, status and prospect of the CFB technology.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.10
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• pp.1075-1081
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• 2011

A leak-detection method has been developed by measuring the pressure variation between the inner and outer heattransfer tubes of a double-wall tube steam generator. An experiment was carried out to measure the leak rate in the gap between two surfaces pressed with a hydraulic press in order to simulate the phenomena, and a correlation was determined for the leak rate in a micro gap. However, in the correlation, the gap width and friction coefficient were coupled with the surface roughness, which affects the two parameters. The two parameters were separated using a surface-contact model to develop a correlation for the friction coefficient. The correlation was compared with the existing correlations used for crack analysis. Although the applied ranges of Reynolds numbers were different, the developed correlation for Reynolds numbers of 0.1.0.35 showed similar tendencies to existing correlations used for higher Reynolds numbers.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.10
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• pp.1061-1066
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• 2011

In this study, the flow characteristics of an injection nozzle installed in a high-pressure holder for improving productivity were determined. The inlet velocity, nozzle inflow angle, and nozzle outlet diameter were selected as design factors having an influence on the flow characteristics, and numerical analysis was conducted for these factors. As the inlet velocity is high and the nozzle outlet diameter is small, the pressure and velocity of the injected flow are high. In the case of the nozzle inflow angle, the variation of flow characteristics according to angle was slight, but the highest pressure and velocity were found at $15^{\circ}$. In addition, the possibility of chip elimination by the injected flow was analyzed on the basis of the numerical results.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.2
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• pp.1-7
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• 2002

In the modern propulsion systems, requited thrust is obtained using a nozzle. Sometimes shock and induced boundary layer separation is generated in an over-expanded convergent-divergent supersonic nozzle. It occurs because the nozzle expansion ratio is too large for a given nozzle pressure ratio (NPR). This phenomenon can be explained that it redefines effective nozzle geometry, shorer nozzle geometry and lower pressure ratio, in a given pressure ratio. Numerical studies were conducted about a fixed geometry 2D nozzle in overexpanded condition and compared with Hunter's experimental result. For the numerical simulation of the supersonic nozzle, Navier-Stokes equations are considered and as a turbulent model, $\kappa$-$\varepsilon$ /$\kappa$-$\omega$ blended SST two equation turbulent model is used. The characteristics of $\lambda$-shape shock systems due to the interaction of shock and boundary layer was investigated in a low NPR. And the result of comparison of thrust value shows that a fixed geometry nozzle can cover required flight mission.