• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.4
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• pp.321-328
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• 2014

The performance characteristics of a subscale diffuser under non-reacting conditions for high-altitude simulation were numerically investigated with respect to different lengths of the secondary throat diffuser. The ratio of the length of the diffuser entrance to the nozzle exit diameter was set to 0, 50, and 100%. In addition, flow characteristics were studied for a range of length-to-diameter ratios of the secondary throat diffuser. An insufficient diffuser entrance length caused contraction of the plume immediately after the nozzle exit. When the length-to-diameter ratio was less than 8, a strong Mach disk was formed inside the diffuser, resulting in a sharp increase in pressure. In addition, flow characteristics in the diverging part of the diffuser were investigated for a range of diverging part lengths. A short diverging part may lead to abrupt pressure recovery, resulting in the possible application of mechanical load to the diffuser.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.2
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• pp.158-173
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• 1985

An experimental investigation has been made to study the interaction between and incident oblique shock wave and an unstabilized turbulent boundary layer on a solid surface downstream of a porous surface with air injection through the porous surface. The boundary layer upstream of the interaction is unstabilized by the injection and provokes a shock wave which eventually interacts with the unstabilized boundary layer after reflecting from the upper wall of the test section. Three cases having diferent upstream Mach numbers and different shock strengthes are studied. According to the level of the unstabilization, two cases are of attached boundary layers and the other one is of a separated boundary layer. The result shows that the reflected wavey system is composed of the compression wave, expansion wave fan, and recompression wave like the ordinary interaction while the separated boundary layer strengthens the reflected expansion waves. The interactions of the attached boundary layers show a similar tendency of the upstream wall pressure distribution as that of the ordinary interacton but the pressure rise rather decays in the downstream region. In case of the separated boundary layer, the wall pressure continues to rise in the downstream as opposed ot the former cases. This indicates that the interaction region spreads out widely adn the viscous effect of the separated boundary layer smoothens the abrupt pressure increase due to the shock inpingement.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.10
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• pp.125-132
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• 2019

Because the water exposed to shock waves caused by an underwater explosion cannot withstand the appreciable tension induced by the change in both pressure and velocity, the surrounding water is cavitated. This cavitating water changes the transferring circumstance of the shock loading. Three phenomena contribute to hull-plate damage; initial shock loading and its interaction with the hull plate, local cavitation, and local cavitation closure then shock reloading. Because the main concern of this paper is local cavitation due to a near-field underwater explosion, the water surface and the waves reflected from the sea bottom were not considered. A set of governing equations for the structure and the fluid were derived. A simple one-dimensional infinite plate problem was considered to verify this uncoupled solution approach compared with the analytic solution, which is well known in this area of interest. The uncoupled solution approach herein would be useful for obtaining a relatively high level of accuracy despite its simplicity and high computational efficiency compared to the conventional coupled method. This paper will help improve the understanding of fluid-structure interaction phenomena and provide a schematic explanation of the practical problem.