• Title/Summary/Keyword: 공아

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Numerical Analysis on the Turbulence Patterns in The Scour Hole at The Downstream of Bed Protection (하상보호공 직하류부 세굴공의 난류양상에 관한 수치해석적 연구)

  • Lee, Jaelyong;Park, Sung Won;Yeom, Seongil;Ahn, Jungkyu
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.20 no.5
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    • pp.20-26
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    • 2019

  • Where hydraulic structures are to be installed over the entire width of a river or stream, usually a bed protection structure is to be installed. However, a local scour occurs in which the river bed downstream of the river protection system is eroded due to the influence of the upstream flow characteristics. This local scour is dominant in the flow and turbulence characteristics at the boundary of the flow direction and in the material of the bed materials, and may gradually become dangerous over time. Therefore, in this study, we compared the turbulence patterns in the local scour hole at the downstream of the river bed protection with the results of the analysis of the mobile bed experiment, and compared with the application of OpenFoam, a three dimensional numerical analysis model. The distribution of depth-averaged relative turbulence intensities along the flow direction was analyzed. In addition to this result, the stabilization of scour hole was compared with the bed shear stress and Shields parameter, and the results were compared by changing the initial turbulent flow conditions. From the results, it was confirmed that the maximum depth of generation of the three-stage was dominantly developed by the magnitude of depth-averaged relative turbulence intensity rather than the mean flow velocity. This result also suggests that design, construction or gate control are needed to control the depth-averaged relative turbulence intensities in order to reduce or prevent the local scour faults that may occur in the downstream part of the bed protection.

  • https://doi.org/10.5762/KAIS.2019.20.5.20 인용 PDF KSCI HTML

Case Study on Combustion Stabilization in FASTRAC Thrust Chamber Using Acoustic Cavities (FASTRAC 연소기에서 음향공을 이용한 연소불안정 제어 사례 연구)

  • Kim, Hong-Jip;Kim, Seong-Ku
    • Journal of the Korean Society of Propulsion Engineers
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    • v.16 no.5
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    • pp.29-36
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    • 2012

  • 3-D linear acoustic analysis has been performed to elucidate damping characteristics of large Helmholtz acoustic cavities in FASTRAC thrust chamber. Acoustic impedance concept has been introduced to quantify combustion stabilization capacity. For a given acoustic cavity, sonic velocity in the cavity to achieve an optimal tuning has been determined and satisfactory agreement with the previous results has been obtained. Feasible estimation of sonic velocity in the acoustic cavity has been devised. Results show similar trends without significant deviations, which can be used in the procedure of design and verification of acoustic cavity. From the satisfactory results, investigation of other thrust chambers with acoustic cavities which have shown combustion instabilities will be done as future works.

  • https://doi.org/10.6108/KSPE.2012.16.5.029 인용 PDF KSCI