• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.5
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• pp.456-465
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• 2015

Dual-bell nozzle can overcome the performance losses of the conventional bell-shaped nozzles which induced by off-design operations with either over-expanded or under-expanded exhaust flow and minimize the losses of the specific impulse. In United States, Rocketdyne analyzed thrust characteristics according to the shape of the expansion nozzle and NASA conducted hot firing tests with various altitudes. DLR, which is one of the research institute of the Europe, is carrying out research for the different cases of inflection angle, nozzle length and expansion ratio. MAI of Russia applied the slot nozzle to the expansion region in order to reduce the performance losses. In Asia, both the Japan and the India are researching on the dual-bell nozzle and Mitsubishi cooperation of the Japan registered its patent. In this paper, concepts and performance of dual-bell nozzle, which can compensate altitude, are investigated and trends of current research are summarized. It is necessary for Korea to research on the dual-bell nozzle for lucrative space development.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.3
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• pp.304-314
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• 2004

An experimental study has been conducted to measure the temperature fields and the local film cooling effectiveness for two and three staggered rows of the rectangular shaped-holes with various blowing rates. The hydraulic diameter of rectangular-shaped hole is 10mm. To compare with the film cooling performance of rectangular-shaped hole, two kinds of circular holes are tested. One has the same hydraulic diameter as the rectangular hole and the other has the same cross sectional area. Also, rectangular holes with expanded exit with same inlet area as rectangular ones are tested. Temperature fields are measured using a thermocouple rake attached on three-axis traversing system. Adiabatic film cooling effectiveness on the surface are obtained based on experimental results of thermochromic liquid crystals. The film cooling effectiveness is measured for various blowing rates and compared with the results for the cylindrical holes. In case of 2 rows, the rectangular holes has better performance than circular holes due to its slot-like geometry. In case of 3 rows, the effecta of hole shape is not clear.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.192-197
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• 2004

Recently, fluidic thrust vectoring methods have been preferably employed to control the movement of propulsive systems due to relatively simpler design and lower cost than mechanical thrust vectoring methods. For An application of the thrust vectoring to flight bodies, it is necessary to understand very complicated exhaust flows which are often subject to shock waves and boundary layer separation. But researches for the thrust vector control using counterflow have been few. In the present study, experiments have been performed to investigate the characteristics of supersonic jets controlled by a thrust vectoring method using counterflow. The primary jet is expanded through a two-dimensional primary nozzle shrouded by collars, and is deflected by the suction of the air near nozzle into an upper slot placed between the primary nozzle and the upper collar. A shadowgraph method is used to visualize the supersonic jet flowfields. Primary nozzle pressure ratios and suction nozzle pressure ratios are varied from 3.0 to 5.0, and from 0.2 to 1.0 respectively. The present experimental results showed that, for a given primary nozzle pressure ratio, a decrease in the suction nozzle pressure ratio produced an increased thrust vector angle. As the suction nozzle pressure ratios were increased and decreased, the hysteresis of the thrust vectoring was observed through the wall pressure distributions

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.3 s.118
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• pp.305-314
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• 2007

In this paper, we suggested a CPW-fed UWB antenna with uni-planar sectoral structure. The area where radiation device face ground is designed to have the shape of tapered slot based on exponential function. We modified a rectangular bow-tie dipole structure antenna and thus formed a multi-resonant mode. From this, we expanded the impedance bandwidth and made a feature satisfying VSWR of less than 2 between $3.1\sim10.6GHz$. The test result showed that the return loss less than -10 dB was met in the full-band UWB system and maximum gain of $0.9\sim3.1dB$ was made with the half-power beamwidth of $40.1\sim89.9^{\circ}$ on XY plane(Theta, $Phi=90^{\circ}$) and the full band. By using CPW-fed structure with no ground on the back of the substrate, the suggested antenna is easy to design and its miniaturization is also possible.