• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.3
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• pp.61-68
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• 2010

A small high altitude test facility has been developed to investigate ignition performance of a small gas-turbine combustor under high altitude conditions. Supersonic diffusers and a heat exchanger were used to perform a low pressure and a low temperature condition, respectively. Experimental results showed that the low pressure environment could be controlled by upstream pressure of primary nozzle flow and low temperature environment by mixture ratio of cooled air and ambient air. Ignition performance tests were performed to verify the performance of the facility under simulated high altitude conditions. Conclusively, it was proven that the test facility could be used for ignition performance test of a small gas-turbine combustor under high altitude condition of approximately 6,100m.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.10a
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• pp.33-33
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• 1999

The Coanda effect is the tendency for a fluid jet to atach itself to an adjacent surface and follow its contour without causing an appreciable flow separation. The jet is pulled onto the surface by the low pressure region which develops as entrainment pumps fluid from the region between the jet and the surface. Then the jet is held to the wall surface by the resulting radial pressure gradient which balance the inertial resistance of the jet to turning. The jet may attach to the surface and may be deflected through more than 180 dog, when the radius of the Coanda surface is sufficiently large compared to the height of the exhaust nozzle. However, if the radius of curvature is small, the jet turns through a smaller angle, or may not attach to the surface at all. In general, the limitations in size and weight of a device will limit the radius of the deflection surface. Thus much effort has been paid to improve the jet deflection in a variety of engineering fields. The Coanda effect has long been applied to improve aerodynamic characteristics, such as the drag/lift ratio of flight body, the engine exhaust plume thrust vectoring, and the aerofoil/wing circulation control. During the energy crisis of the seventies, the Coanda jet was applied to reduce vehicle drag and led to drag reductions of as much as about 30% for a trailer configuration. Recently a variety of industrial applications are exploiting another characteristics of the Coanda jets, mainly the enhanced turbulence levels and entrainment compared with conventional jet flows. Various industrial burners and combustors are based upon this principle. If the curvature of the Coanda surface is too great or the operating pressure too high, the jet flow will break away completely from the surface. This could have catastrophic consequences for a burner or combustor. Detailed understanding of the Coanda jet flow is essential to refine the design to maximize the enhanced entrainment in these applications.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.287-293
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• 2004

A numerical simulation is presented for investigating the effects of pressure ratio of $D_2$ injector to supersonic nozzle on the population inversion in the DF chemical laser cavity, while a lasing concurrently takes place. The laser beam is generated between the mirrors in the cavity and it is important to obtain stronger population inversion and more uniform distribution of the excited molecules in the laser cavity in order to produce high power laser beam with good quality. In this study, these phenomena are investigated by means of analyzing the distributions of the DF excited molecules and the F atom used as an oxidant, while simultaneously estimating the maximum small signal and saturated gains and power in the DF chemical laser cavity. For the numerical solution, an 11-species (including DF molecules in various excited states of energies), 32-step chemistry model is adopted for the chemical reaction of the DF chemical laser system. The results are discussed by comparison with two $D_2$injector pressure cases; 192 torr and 388.64 torr. Major results reveal that in the resonator, stronger population inversions occur in the all transitions except DF(1)-DF(0), when the $D_2$injection pressure is lower. But, the higher $D_2$injection pressure provides a favorable condition for DF(1)-DF(0) transition to generate the higher power laser beam. In other words, as the pressure of $D_2$injector increases, the maximum small signal gain in the $V_{1-0}$ transition, which is in charge of generating most of laser power, becomes higher. Therefore, the total laser beam power becomes higher.r.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.11
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• pp.753-760
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• 2019

Sparkjet actuator, also known as plasma synthetic jet actuator, which is a kind of active flow control actuator is considered as being high possibility for the supersonic flow control due to ejecting stronger jet compared to the other active flow control actuators. Sparkjet actuator generates high temperature and high pressure flow inside the cavity by using arc plasma and leads momentum by ejecting such flow through orifice or nozzle. In this research, numerical calculation of sparkjet actuator with respect to the location of electrodes which exists inside the cavity is conducted and the change of the performance of sparkjet actuator is suggested. As the location of electrodes goes closer to the bottom of the cavity, impulse is increased and the average pressure inside the cavity maintains higher. When the location of electrode is 25% and 75% of the entire cavity height, impulse is 2.515 μN·s and 2.057 μN·s, respectively. Each impulse is changed by about 9.92% and -10.09% compared to when the location of electrodes is 50% of the entire cavity height.

• Proceedings of the Korean Vacuum Society Conference
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• 1998.02a
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• pp.120-120
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• 1998

Boron nitride (BN) films have attracted a growing interest for a variety of t technological applications due to their excellent characteristics, namely hardness, c chemical inertness, and dielectrical behavior, etc. There are two crystalline phases 1551; of BN that are analogous to phases of carbon. Hexagonal boron nitride (h-BN) has a a layered s$\sigma$ucture which is spz-bonded structure similar to that of graphite, and is t the stable ordered phase at ambient conditions. Cubic boron nitride (c-BN) has a z zinc blende structure with sp3-bonding like as diamond, 따ld is the metastable phase a at ambient conditions. Among of their prototypes, especially 삼Ie c-BN is an i interesting material because it has almost the same hardness and thermal c conductivity as di없nond. C Conventionally, significant progress has been made in the experimental t techniques for synthesizing BN films using various of the physical vapor deposition 밍ld chemical vapor deposition. But, the major disadvantage of c-BN films is that t they are much more difficult to synthesize than h-BN films due to its narrow s stability phase region, high compression stress, and problem of nitrogen source c control. Recent studies of the metalorganic chemical vapor deposition (MOCVD) of I III - V compound have established that a molecular level understanding of the d deposition process is mandatory in controlling the selectivity parameters. This led t to the concept of using a single source organometallic precursor, having the c constituent elements in stoichiometric ratio, for MOCVD growth of 삼Ie required b binary compound. I In this study, therefore, we have been carried out the growth of h-BN thin f films on silicon substrates using a single source precursors. Polycrystalline h-BN t thin films were deposited on silicon in the temperature range of $\alpha$)() - 900 $^{\circ}$C from t the organometallic precursors of Boron-Triethylamine complex, (CZHs)3N:BRJ, and T Tris(dimethylamino)Borane, [CH3}zNhB, by supersonic molecular jet and remote p plasma assisted MOCVD. Hydrogen was used as carrier gas, and additional nitrogen w was supplied by either aDlIDonia through a nozzle, or nitrogen via a remote plasma. T The as-grown films were characterized by Fourier transform infrared spectroscopy, x x-ray pthotoelectron spectroscopy, Auger electron spectroscopy, x-ray diffraction, t transmission electron diffraction, optical transmission, and atomic force microscopy.roscopy.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.2
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• pp.45-52
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• 2002

An experimental investigation on the structure and dynamic behavior of two dimensional over-expanded air jets exiting into water was carried out. The hish speed digital video imaging and static pressure distribution measurement were made to characterize the structure and time-dependant behavior of the jets. Mach number at the jet exit was 2.0 and was slightly less than the value predicted by the ideal nozzle calculation. Variance of jet spreading angle at different stagnation condition was measured as a function of mass flow rate. Periodic nature of the air jet distortion in water was observed and the frequency of the repetition was approximately 5-6 Hz for all cases tested. Three characteristic length scales were defined to characterize jet structure. $L_1$, maximum width of the plume when the periodic instability occurs, $L_2$, width of the jet where secondary reverse flow entrained jet flow and $L_3$, distance from the jet exit to the location where entrainment of the secondary reverse flow occurs. The ratio of $L_1$ and $L_2$ decreased with increasing stagnation pressure, i.e. mass flow rate. $L_3$ increased with increasing stagnation pressure. The temporal behavior of static pressure measurements also showed peak around frequency of 5, which corresponds the frequency obtained by visual measurements