• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.4
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• pp.290-296
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• 2018

In this study, the cold test and the numerical analysis were carried out according to the shape parameters of the test model in order to confirm the operation range of high altitude environment simulation test facility for the supersonic vehicle. The blockage ratio, angle and length ratio were considered as the design parameters. The blockage rate is expected to be limited in the region of more than 40% due to the normal shock and expansion fan. It was confirmed that the angle of model should be selected at the size of 45 degrees or less due to the influence of the strong shock wave. There was no difference in performance between the lengths of 8 times the model diameter. Finally, we obtained the performance database according to the shape parameters of the conical test model and confirmed the operable range of the semi-freejet type high altitude environment simulation test facility.

• Journal of Aerospace System Engineering
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• v.16 no.5
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• pp.17-25
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• 2022

The pintle injector has many advantages in the key characteristics of a liquid rocket engine, such as combustion stability, combustion efficiency, and wide range of comprehensive thrust control, design and manufacture, and test fired under supercritical conditions. The pintle injector is manufactured with a rectangular, single-row orifice for thrust control and production considerations. In order to verify the combustion performance of the pintle injector and its potential as a commercial injector, the combustion characteristics were analyzed by varying the TMR (Total Momentum Ratio) and BF (Blockage Factor). The result of the hot firing test showed that the heat flux increased as TMR increased, and it confirmed that the characteristic velocity efficiency was more affected by BF than TMR. Suppose a single-row pintle injector with efficiency characteristics insensitive to changes in TMR can achieve high efficiency at low fuel differential pressure conditions. In that case, the variable pintle injector's design flexibility can be increase.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.1
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• pp.62-70
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• 2009

In this paper, the fluid flow behavior past a pair of rectangular cylinders placed in a two dimensional horizontal channel has been investigated using Lattice-Boltzmann Method(LBM). The LBM has built up on the D2Q9 model and the single relaxation time method called the Lattice-BGK(Bhatnagar-Gross-Krook)model. Streamlines, velocity, vorticity and pressure contours are provided to analyze the important characteristics of the flow field for a wide range of non dimensional parameters that present in our simulation. Special attention is paid to the effect of spacing(d) between two cylinders and the blockage ratio A(=h/H), where H is the channel height and h is the rectangular cylinder height. for different Reynolds numbers. The first cylinder is called upstream cylinder and the second one as downstream cylinder. The downstream fluid flow fields have been more influenced by its blockage ratios(A) and Reynolds numbers(Re) whereas the upstream flow patterns(in front of downstream cylinder) by the gap length(d) between two cylinders. Moreover, it is observed that after a certain gap, both upstream and downstream flow patterns are almost similar size and shape. The simulation result has been compared with analytical solution and it is found to be in excellent agreement.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.1
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• pp.71-82
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• 2002

A time-iterative compressible Navier-Stokes code is developed to analyze the flowfield of a two-dimensional ejector nozzle system. A parametric study has been made for two controlling parameters, duct to nozzle area ratio and nozzle pressure ratio. Results show that there is an optimum area ratio for an efficient pumping of secondary flow. At high area ratios, a freestream flow directly passes through the mixing duct without giving adequate pumping. While at low area ratios, jet boundary is acting as a blockage to incoming flow. The nozzle pressure ratio variation shows that the pumping rate increases as the pressure ratio increases provided there is no interaction between the shroud wall and the shock cell structure.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.4
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• pp.397-404
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• 2012

In this research, a numerical study was carried out on the mixing and flow characteristics of a vane-type static mixer for the reduction of $NO_x$ in the SCR systems from the diesel exhaust environments. The mixer was located at a distance of 57 times the pipe diameter away from the inlet. The analyses were performed by changing various parameters such as vane angles, blockage ratio, and location of the vane. Flow characteristics through the mixer were characterized by the uniformity index, swirl number, and pressure drop. The results show that uniformity index, pressure coefficient and swirl number are substantially influenced by the vane angle, blockage ratio and position of the vane of the mixer. In particular, the swirl number was increased when the vane was located near the pipe wall, or the vane angle was increased or scale was extended.

• Nuclear Engineering and Technology
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• v.54 no.3
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• pp.860-866
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• 2022

An accurate prediction of the pressure drop along the flow paths is crucial in the design of advanced passive systems cooled by heavy liquid metal coolants. To date, a generic pressure drop correlation over spacer grids by Rehme has been applied extensively, which was obtained from substantial experimental data with multiple types of components. However, a few experimental studies have reported that the correlation may give large discrepancies. To provide a more reliable correlation for ring-type spacer grids, the current numerical study aims at figuring out the most critical factor among four hypothetical parameters, namely the flow area blockage ratio, number of fuel rods, type of fluid, and thickness of the spacer grid in the flow direction. Through a set of computational fluid dynamics simulations, we observed that the flow area blockage ratio dominantly influences the pressure loss characteristics, and thus its dependence should be more emphasized, whereas the other parameters have little impact. Hence, we suggest a new correlation for the drag coefficient as C_B = C_ν,m/ε^2.7, where C_ν,m is formulated by a nonlinear fit of simulation data such that C_ν,m = -11.33 ln(0.02 ln(Re_b)).

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.6
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• pp.317-323
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• 2013

A multi-perforated tube indicates the existence of multiple holes of various shapes on the surface of a long cylinder-type or rectangular tube, and a hole installed on the surface is called an orifice, as it is relatively small in size, compared with the surface area of the tube. In this study, the flow characteristics of a circular multi-perforated tube with many orifices on the surface were investigated experimentally and numerically. The volume flowrate issuing from each orifice, discharge angle, effective flow area ratio, and the flow fields around the orifices were measured and visualized, with the variation of the orifice area ratio, at the same blockage ratio. The volume flowrate distributions along the flow direction of the multi-perforated tube tends to be more uniform, as larger orifices were positioned at the inlet side of the multi-perforated tube, compared with no orifice area change along the flow direction.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.12
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• pp.3344-3351
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• 1995

The stability of diffusion flame formed behind a bluff body with fuel injection slits was experimentally investigated in various fuel injection angles, fuel injection ratios, grids and extension ducts. The flame stability limits, temperature distributions and length of recirculation zones, direct photographs of flames were measured in order to discuss the stabilization mechanism of the diffusion flame. The results from this study are as follows. The fuel injection angle is an important factor in determining the flame stability. Stability limits can be improved by variety of the fuel injection ratio. When the grid and extension duct are set, stability characteristics are varied with the blockage ratios, grid intervals, and grid numbers. The recirculation zone not only serves as a steady ignition source of combustion stream but also governs the stabilization mechanism.

• International Journal of Fluid Machinery and Systems
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• v.8 no.3
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• pp.124-131
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• 2015

The good performance of a vortex shedder is defined by strong and stable vortex generated under the condition of most linearity in Strouhal number and low power loss. In this paper, the flow past a bluff body of circular cylinder with a slit normal to the flow has been analyzed focusing on drag coefficient, linearity of Strouhal number and flow resistance (K-factor). The ANSYS/FLUENT package is used for flow simulation and the integration method of computational code to iSIGHT platform is employed for automated design cycle. This study results the design with (0.20~0.267) blockage ratio and 0.10 slit ratio as the best shedder for vortex flowmeter and this results are in well agreement with the experiment. As the combination of GAMBIT, FLUENT, and iSIGHT substitutes the design parameters automatically according to the input data, this method designs effectively the vortex shedder with less design cycle time and low manufacturing cost eliminating the human intervention bottleneck.

• Proceedings of the KSR Conference
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• 2000.11a
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• pp.506-513
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• 2000

The tunnel booming noise generated by a train moving into a tunnel has been one of the most serious constraints in the development of the high-speed trains. It is well known that the nose shape of the train has the significant influence on the intensity of the booming noise. In this study, the nose shape has been optimized by using the response surface methodology and the axi-symmetric compressible Euler equations. The parametric studies are also performed with respect to the slenderness ratio, the blockage ratio and the train speed to investigate their sensitivities to the optimization results. The results show that it is possible to define more general design space by introducing the Hicks-Henne shape functions, resulting in the more effective nose shape than that of Maeda. The mechanism and the aspects of the train-tunnel interaction were also investigated from the results of the parametric study.