• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.4
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• pp.79-84
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• 2005

An experimental investigation for impingement of under-expanded, axisymmetric jets on a flat plate has been conducted, and the surface pressure, the adiabatic wall temperature distributions on the plate have been measured in detail. For the explanation on the wall temperature distributions, the total temperature distributions along a free jet have also been measured with total temperature probes. In this study, the under-expansion ratio and the nozzle-to-plate distance have been considered as experimental parameters. Depending on nozzle-to-plate distances, different distributions of adiabatic wall temperature are shown by the energy separation at a jet edge and a impinged surface. Also, the recovery factor on a stagnation point decreases significantly due to the isolation of fluid particles in a central region.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1631-1636
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• 2004

The supersonic impinging jet has been extensively applied to rocket launching system, gas jet cutting control, gas turbine blade cooling, etc. In such applications, wall temperature of an object on which supersonic jet impinges is a very important factor to determine the performance and life of the device. However, wall temperature data of supersonic impinging jets are not enough to data. The present study describes an experimental work to measure the wall temperatures of a vertical flat plate on which supersonic, dual, coaxial jet impinges. An Infrared camera is employed to measure the wall temperature distribution on the impinging plate. The pressure ratio of the jet is varied to obtain the supersonic jets in the range of over-expanded to moderately under-expanded conditions at the exit of coaxial nozzle. The distance between the coaxial nozzle and the flat plate was also varied. The coaxial jet flows are visualized using a Shadow optical method. The results show that the wall temperature distribution of the impinging plate is strongly dependent on the jet pressure ratio and the distance between the nozzle and plate.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.377-381
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• 2006

This paper describes experimental work to control supersonic jet noise using a mesh screen that is placed at the nozzle exit plane. The mesh screen is a wire-gauze screen that is made of long stainless wires with a very small diameter. The nozzle pressure ratio is varied to obtain the supersonic jets which are operated in a wide range of over-expanded to moderately under-expanded jets. In order to perturb mainly the initial jet shear layer, the hole is perforated in the central part of the mesh screen. The hole size is varied to investigate the noise control effectiveness of the mesh screen. A schlieren optical system is used to visualize the flow fields of supersonic jet with and without the mesh screen device. Acoustic measurement is performed to obtain the OASPL and noise spectra. The results obtained show that the present mesh screen device leads to a substantial suppression of jet screech tones. The hole size is an important factor in reducing the supersonic jet noise. For over-expanded jets, the noise control effectiveness of the mesh screen appears more significant, compared to correctly and under-expanded jets

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.8
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• pp.84-91
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• 2005

An experimental investigation has been carried out to examine heat-transfer characteristics of an axisymmetric, under-expanded, sonic jet impinging on a flat plate and the local measurement of surface pressures and heat transfer coefficients on a plate have been achieved together with a visualization test of shock structure in a jet. Heat transfer coefficients on a plate have been found to be changed significantly depending on the under-expansion ratio as much as the nozzle-to-plate distance. These phenomena could be explained by the wall pressure measurement and the shock visualization.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.165-172
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• 2004

LE-7A is the main engine of the H-IIA launch vehicle. Under its development, the nozzle suffered from two troubles during startup and shutdown transients of the engine. One is a large side load, which damages the actuator of the nozzle, and the other is damage on regenerative cooling tubes due to high heat load. It has been considered that these problems are caused by a peculiar separation pattern called Restricted Shock Separation (RSS). RSS is observed in several rocket nozzles, for example, LE-7A nozzle, Vulcain nozzle and so on. Their contours are not conventional truncated perfect (TP) nozzle - LE-7A nozzle is a compressed truncated perfect (CTP) nozzle and Vulcain nozzle is a thrust optimized (TO) nozzle. Although it is believed that the occurrence of RSS is affected by the nozzle contour, the mechanisms are not clarified sufficiently yet. In the present paper, a parametric numerical study is carried out to investigate the mechanisms of the occurrence of RSS in CTP nozzles during startup transient. The results show that RSS is caused by the adverse pressure gradient downstream of the Mach disk. The adverse pressure gradient is caused by the interaction of the pressure wave and Mach disk. The method to avoid the occurrence of RSS is also examined. A small step inside the nozzle affects the position of the separation point and prevents RSS. The result shows that the possibility that RSS can be suppressed by controlling the position of the separation point.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.10
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• pp.112-117
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• 2004

This work is on numerical and experimental studies on the new type igniter using aerodynamic energy. The aerodynamic igniter consists of a nozzle and a resonance tube. The supersonic jet from a nozzle coming into the resonance tube generates pressure oscillation between the nozzle and the resonator. This oscillation changes the kinetic energy to thermal energy in the resonator under a certain condition. In this study, sonic and supersonic nozzles were tested in two different resonators, results has been compared. And geometrical optimum values of a supersonic nozzle has been suggested to reduce aerodynamic loss and friction in the expanded surface of the nozzle.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.586-591
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• 2003

The present study addresses experimental results to investigate the effect of the jet supply chamber configuration on the sonic/supersonic swirling jets, as the case study. The experiment is carried out using the convergent nozzle with a various different chamber configurations upstream the nozzle throat, which is composed of four tangential inlet holes for the swirling flows. The jet pressure ratio is varied between 3.0 and 7.0. The sonic/supersonic swirling jet flows are specified by the pitot impact and static pressure measurements and visualized using the Shadowgraph method. The results show that the major structures of the sonic/supersonic swirling jet are strongly influenced by the jet supply chamber.

• Fire Science and Engineering
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• v.19 no.2 s.58
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• pp.37-44
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• 2005

We have conducted a numerical simulation under three-dimensional unsteady conditions in order to analyze the characteristics of flow and the distribution of $CO_2$ agent concentration according to the number of $CO_2$ agent nozzle. The engine room of a ship was selected as a protection space, and flow fields and $CO_2$ concentration fields were measured. In case of increasing the number of $CO_2$ nozzle from 2 nozzles to 4 nozzles, the distribution of CO2 concentration showed low, and in case of increasing the number of $CO_2$ nozzle to above 6 nozzles, the recirculating flow affected to all region was generated. In case of increasing the number of $CO_2$ agent nozzle to above 4 nozzles, the iso-concentration line below 0.36 expanded or contracted slightly. Therefor, the proper number and the arrangement of $CO_2$ agent nozzle are considered when $CO_2$ fire fighting system is designed.

• Journal of Powder Materials
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• v.2 no.2
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• pp.120-134
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• 1995

The behavior of the flow about gas atomizers with a supersonic nozzle containing an under-expanded or over-expanded jet is very important with respect to performance and stability characteristics. Since detailed experiments are expensive, computational fluid mechanics have been applied recently to various relating flow field. In this study, a higher order upwind method with the 3rd order MUSCL type TVD scheme is used to solve the full Reynolds Wavier-Stokes equations. To delineate the purely exhaust jet effects, the melt flow is not considered. Comparison is made with some experimental data in terms of density fields. The influence of the exhaust-jet-to freestream pressure ratio and the effect of the protrusion length of the melt orifice are studied. The present study leads us to believe that the computational fluid mechanics should be considered as powerful tool in predicting the gas atomizer flows.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1499-1504
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• 2004

The effects of absorbing materials on the characteristics of supersonic jet noise were experimentally investigated using a convergent-divergent nozzle with a design Mach number of 2.0. Overall sound pressure levels (OASPL) and noise spectra were obtained at far-field locations. Schlieren optical system was used to visualize the flow-fields of supersonic jets. In order to investigate the effect of absorbing materials, baffle plates of different materials (metal, grass wool and polyurethane foam) were installed at the exit of the nozzle. Experiment was carried out over a wide range of nozzle pressure ratios from 2.0 and 18.0, which corresponds to over- and under-expanded conditions. The results obtained show that the screech tone amplitude and the overall sound pressure level reduce by using the baffle plates of absorbing materials, compared with the metal baffle plate. It is also found that the characteristics of supersonic jet noise are strongly dependent on the size of baffle plate.