• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.445-450
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• 2011

Swirling flows inside a swirl mixing chamber are investigated for simple configuration where swirl is produced by a tangential entry type swirl generator. The flow downstream of the swirl generator has been quantified by measurements two velocity components and their corresponding mean values along axial and radial direction using Particle Image Velocimetry(PIV). The mass flow rate of the tangential entry is increased in order to study their effect on the flow field. From the measurement profile of velocity and vorticity, flow mixing characteristics in a swirl mixing chamber are evaluated.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.4
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• pp.326-335
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• 2014

Aerodynamic characteristics of the small two-stage turbo blower were investigated using commercial CFD tool(ANSYS CFX Ver. 14.5) in this paper. Turbo blower, which is a centrifugal type of turbomachinery, is used in various industries. It is used for application that required high static pressure rising at relatively small volumetric flow rate. In order to understand the mechanism of static pressure rising, the aerodynamic characteristics of the small two-stage turbo blower are analyzed at high rotating speed in this study. The k-${\omega}$ SST turbulence model, which is good at prediction of adverse pressure gradient flows, was applied. The CFD results of the turbo blower are validated by performance test. The static pressure rising of the turbo blower is nonlinearly increased over the first stage and the second stage. The secondary flow occurred at guide vanes, between the casing and the first impeller shroud, and the bottom of the impeller disk. As a result, It is required that whole fluid area is analyzed to predict aerodynamic characteristics of small two-stage turbo blower. and the result should be selected with considering for error from experiment and CFD.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.4
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• pp.42-52
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• 1997

The basic principle of underwater ram-jet as a unique marine propulsion concept showing vary high cruise speed range(e. g. 80-100 knots) is the thrust production by the transfer of the potential energy of compressed gas to the operating liquid through kinetic mixing process. This paper is aimed to investigate the propulsive efficiency of the nozzle flow in underwater ram-jet at the speed of 80 knots for the buried type vessel. The basic assumption of the theoretical analysis is that mixture of water and air can be treated as incompressible gas. For an optimized nozzle configuration obtained from the performance analysis, preliminary data for performance evaluation are obtained and effects of nozzle inner wall friction, ambient temperature, ambient pressure, water density, gas velocity, bubble radius, flow velocity, diffuser area ratio, mass flow ratio and water velocity gradient are investigated.

• Journal of Aerospace System Engineering
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• v.16 no.4
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• pp.1-9
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• 2022

A design factor analysis was conducted to reduce the thrust reduction in the off-design, due to the driving of the aerospike pintle nozzle. The close (NPR 100) as well as the open (NPR 11) stroke were fixed, as under-expansion conditions. The pintle contour, pintle head radius (R), cowl angle (θ), and cowl exit length (L) were selected as design factors. The change in thrust was analyzed, using a verified numerical analysis technique. First, the pintle head radius and the length of the cowl exit had little influence on the thrust. The cowl angle changed the mass flow rate by affecting the effective nozzle throat area, and created a reverse pressure gradient at the cowl exit. As a result of applying the dual aerospike contour, it was confirmed that the thrust in the design-off increased by approximately 1.2%, compared to the reference case and by approximately 3.4% compared to the worst case.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.2
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• pp.141-151
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• 2015

A new rock excavation method using an abrasive injection waterjet system has been developed to enhance the efficiency and reduce the vibration of tunnel excavation. The abrasive feed rate is an important factor for the cutting performance and the economical efficiency of waterjet-based excavation. In this study, various experiments were performed to explore the effects of major process parameters for both the abrasive feed rate and the suction pressure occurring inside the mixing chamber when the abrasives are inhaled. Experimental results reveal that the abrasive feed rate is affected by geometry parameters (abrasive pipe height, length, and tortuosity), abrasive parameters (abrasive particle size), and jet energy parameters (water pressure and water flow rate). In addition, the relation between the cutting performance and the abrasive feed rate was discussed on the basis of the results of an experimental study. The cutting performance can be maximized when the abrasive feed rate is controlled appropriately via careful management of major process parameters.