• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.265-271
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• 2007

A small supersonic wind tunnel was designed and built to study the flow characteristics of a supersonic impulse turbine cascade. Experiments were performed to find the flow characteristics of a supersonic turbine with the cascade positions and to find a factor of the expansion loss. The supersonic cascade with a 2-dimensional supersonic nozzle was tested with the cascade positions. The flow was visualized by a Z-type Schlieren system. The static pressures at the turbine cascade inlet and outlet were measured by pressure transducers and a pressure scanner. Also, The total pressures at the turbine cascade back flow were measured. Highly complicated flow patterns including shocks, nozzle-cascade interaction and shock boundary layer interactions of the supersonic turbine were observed. And the flow characteristics in the supersonic turbine with the cascade positions were observed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.7
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• pp.539-549
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• 2017

In this paper, experimental studies on the shroud separation were performed to investigate characteristics of the shroud separation at mach 3. Shroud separation tests were carried out in the vertical free-jet wind tunnel that is capable of testing separable structures. A shroud model was miniaturized to meet test objectives and test section dimensions of the wind tunnel. Pneumatic Locking and separation mechanisms were designed considering external force due to free stream. High speed cameras were used to record the shroud motion and unsteady shock patterns over the deploying shrouds during the shroud separation process. Also, unsteady pressures on the nose surface were measured by using the pressure sensors. Through the tests, the measurement data necessary for researches on the shroud separation technology were obtained. Shroud separation behaviors and characteristics of unsteady pressure on the nose surface for each external flow conditions were analyzed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.634-643
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• 2004

In this paper are presented a concept of a new supersonic air inlet, which is designated a Multi-Row Disk (MRD) inlet, aiming at performance improvement under off-design conditions, and results of wind tunnel tests examined performance characteristics of the MRD inlet. The MRD inlet is frequently called ‘a skeleton inlet’ because of its appearance. The performance of a conventional axisymmetric inlet with a solid center body (spike) deteriorates under off-design Mach number conditions. It is due to the fact that total pressure recovery (TPR) governed by the throat area of inlet and mass capture ratio (MCR) governed by an incidence position of an oblique shock from the spike tip into the cowl can not be controlled independently in such air inlet. The MRD inlet has the spike that is composed of a tip cone and several disks arranged downstream of it, based on the experimental fact that several deep cavities on a conical surface have little negative effect on the boundary layer growth. The overall spike length of the MRD inlet is adjustable to the given flight speed by changing space between disks so that a spillage flow can be controlled independently from controlling the throat area. It could be made clear from the result of wind tunnel tests that the MRD inlet improves TPR by 10% compared with a conventional inlet with a solid spike under off-design conditions.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.644-648
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• 2004

In the present study were examined numerically and experimentally the off-design performance characteristics on an axisymmetric plug nozzle with variable throat area. In this nozzle concept, its throat area can be changed by translating the plug into the axial direction. First, a mixed-expansion plug nozzle, in which two expansion parts are arranged both inside and outside, was designed by means of the method of characteristics. Second, the CFD analysis was verified by the cold-flow wind tunnel test. Third, its performance characteristics were evaluated over a wide range of pressure ratio from half to double throat area through the design point, using the CFD code verified by the wind tunnel tests. It was made clear from the study that not so critical thrust efficiency losses were found and the maximum thrust efficiency loss was at most approximately 5 % under off-design conditions without external flow. This result shows that a plug nozzle can give the altitude compensation even under off-design geometry operations. However, shock waves were observed in the inner expansion part under the doubled throat area operation and thus some thermal problems may be caused on the plug surface. Furthermore, collapse of cell structure on the plug surface was observed with external flow (around Mach number 2.0) as it became lower pressure ratio below the design point and the fact may result in big efficiency loss regardless of geometrical configuration.

• Geomechanics and Engineering
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• v.23 no.6
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• pp.513-521
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• 2020

In this paper, due to the need for cutting cement-soil group pile composite foundation under the 7-story masonry structure of Zhenghe District and the shield tunnel of Zhengzhou Metro Line 5, a field test was conducted to directly cut cement-soil single pile composite foundation with diameter Ф=500 mm. Research results showed that the load transfer mechanism of composite foundation was not changed before and after shield tunnel cut the pile, and pile body and the soil between piles was still responsible for overburden load. The construction disturbance of shield cutting pile is a complicated mechanical process. The load carried by the original pile body was affected by the disturbance effect of pile cutting construction. Also, the fraction of the load carried by the original pile body was transferred to the soil between the piles and therefore, the bearing capacity of composite foundation was not decreased. Only the fractions of the load carried by pile and the soil between piles were distributed. On-site monitoring results showed that the settlement of pressure-bearing plates produced during shield cutting stage accounted for about 7% of total settlement. After the completion of pile cutting, the settlements of bearing plates generated by shield machine during residual pile composite foundation stage and shield machine tail were far away from residual pile composite foundation stage which accounted for about 15% and 74% of total settlement, respectively. In order to reduce the impact of shield cutting pile construction on the settlement of upper composite foundation, it was recommended to take measures such as optimization of shield construction parameters, radial grouting reinforcement and "clay shock" grouting within the disturbance range of shield cutting pile construction. Before pile cutting, the pile-soil stress ratio n of composite foundation was 2.437. After the shield cut pile is completed, the soil around the lining structure is gradually consolidated and reshaped, and residual pile composite foundation reaches a new state of force balance. This was because the condensation of grouting layer could increase the resistance of remaining pile end and friction resistance of the side of the pile.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.1
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• pp.61-69
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• 2004

This paper describes numerical efforts to characterize the flame-holding and air-fuel mixing process of model SCRamjet engine combustor, where a hydrogen jet injected into a supersonic cross flow and in a cavity Combustion phenomena in a model SCRamjet engine, which has been experimentally studied at University of Queensland and Australian National University using a free-piston shock tunnel, was observed around separation region of upstream of the normal injector and inside of cavity. The results show that the separation region and cavity generates several recirculation zones, which increase the fuel-air mixing. Self ignition occurs in the separation-freestream and cavity-freestream interface.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.361-366
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• 2006

A small supersonic wind tunnel was designed and built to study the flow characteristics of a supersonic impulse turbine cascade. The supersonic cascade with a 2-dimensional supersonic nozzle was tested for the leading edge chamfer angle $(\gamma)$ of the supersonic turbine that is the one of the turbine design parameter. Firstly, the flow was visualized by a single pass Schlieren system. Next, total and static pressure of the cascade were measured by a pressure scanning system. Finally, highly complicated flow patterns including shocks, nozzle-cascade interaction and shock boundary layer interactions, flow characteristics of the supersonic turbine were observed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.613-617
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• 2011

Korea Aerospace Research Institute has been designed and manufactured various thurst nozzles of the scramjet engine for optimized configuration. The test campaign for thurst nozzle characteristics was performed at T4 free-piston shock tunnel in University of Queensland, Australia. Total 8 kinds of thrust nozzles and 2 kinds of side walls were manufactured for this campaign. In this paper, the design and specification of thrust nozzles was reported. Based on the static pressure distribution of the engine and pitot pressure distributions at nozzle exit, The positive net thurst was observed with baseline case of the test campaign.

• Tunnel and Underground Space
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• v.16 no.6 s.65
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• pp.476-485
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• 2006

During blasting, both shock wave and gas are generated in detonation process of explosives and the generated wave and gas expansion may create new fractures and damage rock mass. In order to explain and understand completely the fracture mechanism by blasting, we have to consider both effects of the wave and gas expansion simultaneously. In this study, we use a discrete element code, PFC2D and develop an algorithm which is capable of modeling both detonation and gas pressures acting on blasthole wall and visualizing generated cracks within rock mass. Moreover, the gas-pressure modeling method which applies a corresponding external force of gas pressure to parent particles of radial fractures is adopted to simulate a coopting between rock mass and gas penetrating created radial fractures. The developed algorithm is verified by reproducing numerical simulations of a lab-scale test blast successfully.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.119-122
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• 2002

In general, Liquid Injection Thrust Vector Control(LITVC) is accomplished by injecting a liquid into the supersonic exhaust flow through holes in the wall of the propulsion nozzle. This injection flow field is highly complicated and detailed flow physics associated with the secondary flow injection should be known far the practical design and use of the LITVC system. The present study aims at understanding the LTTVC flow field and obtaining fundamental design parameters for LITVC. The experimentations were performed in a supersonic blow-down wind tunnel. Compressed, dry air was used for both the main exhaust and injection flows but the pressures of these two flows were controlled independently. The location of the injection holes was changed and the pressures of the two streams were also changed between 2.0 and 15.0 bar. The effectiveness of LITVC was discussed in details using the results of the pressure measurements and flow visualizations