• Title/Summary/Keyword: Pressure boundary

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Numerical Investigation on the Self-Ignition of High-pressure Hydrogen in a Tube Influenced by Burst Diaphragm Shape (튜브 내 고압 수소의 파열막 형상에 따른 자발 점화 현상에 대한 수치해석)

  • Lee, Hyoung Jin;Kim, Sung Don;Kim, Sei Hwan;Jeung, In-Seuck
    • Journal of the Korean Society of Combustion
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    • v.18 no.3
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    • pp.31-37
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    • 2013
  • Numerical simulations are conducted to investigate the feature of spontaneous ignition of hydrogen within a certain length of downstream tube released by the failure of pressure boundaries of various geometric assumption. The results show that the ignition feature can be varied with the shape of pressure boundary. The ignition at the contact region are developed at the spherical pressure boundaries due to multi-dimensional shock interactions, whereas the local ignition is developed in limited area such as boundary layer at the planar pressure boundary conditions. The spontaneous ignition inside the tube can be generated from the reaction region of only boundary layer regardless of existence of the reaction of core region.

Effects of the Inlet Boundary Layer Thickness on the Flow in an Axial Compressor(II) - Loss Mechanism - (입구 경계층 두께가 축류 압축기 내부 유동에 미치는 영향 (II) - 손실구조 -)

  • Choi, Min-Suk;Park, Jun-Young;Baek, Je-Hyun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.8 s.239
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    • pp.956-962
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    • 2005
  • A three-dimensional computation was conducted to make a study about effects of the inlet boundary layer thickness on the total pressure loss in a low-speed axial compressor operating at the design condition ($\phi=85\%$) and near stall condition($\phi=65\%$). Differences of the tip leakage flow and hub corner-stall induced by the inlet boundary layer thickness enable the loss distribution of total pressure along the span to be altered. At design condition, total pressure losses for two different inlet boundary layers are almost alike in the core flow region but the larger loss is generated at both hub and tip when the inlet boundary layer is thin. At the near stall condition, however, total pressure loss fer the thick inlet boundary layer is found to be greater than that for the thin inlet boundary layer on most of the span except the region near hub and casing. Total pressure loss is scrutinized through three major loss categories in a subsonic axial compressor such as profile loss, tip leakage loss and endwall loss using Denton's loss model, and effects of the inlet boundary layer thickness on the loss structure are analyzed in detail.

The effects of tripping structure on the development of turbulent boundary layer subjected to adverse pressure gradient (역압력 구배가 존재하는 난류 경계층의 발달에 트리핑 구조물이 미치는 영향에 관한 연구)

  • 임태현;김대성;윤순현
    • Proceedings of the Korean Society of Marine Engineers Conference
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    • 2001.11a
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    • pp.36-44
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    • 2001
  • The effects of various tripping structures on turbulent boundary layer subjected to adverse pressure gradient were examined. The profiles are compared to zero pressure gradient and adverse pressure gradient. The increases of tripping structures of height, k are affects almost flow parameter included velocity fluctuation, skin friction coefficient and turbulent boundary thickness.

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Response of the Poleward Boundary of the Nightside Auroral Oval to Impacts of Solar Wind Dynamic Pressure Enhancement

  • Cho, Joon-Sik;Lee, Dae-Young;Kim, Kyung-Chan;Lee, Ji-Hee
    • Journal of Astronomy and Space Sciences
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    • v.27 no.3
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    • pp.189-194
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    • 2010
  • In this paper we have investigated latitudinal variations of the poleward boundary of the nightside auroral oval when the magnetosphere is hit by an enhanced solar wind dynamic pressure front. We used precipitating particle data obtained from Defense Meteorological Satellite Program satellites to identify the locations of the boundary before and after enhanced pressure impacts. The boundary locations are represented by a parameter called "b5e". After performing the analysis for a number of events, we found that the basic effect of the solar wind pressure increase impact is often (but not always) to move the poleward boundary of the nightside auroral oval poleward. However, this effect can be often modified by other factors, such as simultaneous variations of the interplanetary magnetic field with a pressure increase, and thus the boundary response is not necessarily a poleward shift in many cases. We demonstrate this with specific examples, and discuss other possible complicating factors.

A solution method for the pressure-based boundary condition in the computation of two-dimensional incompressible viscous flow (2차원 비압축성 점성유동에 나타나는 압력 경계조건의 해결방안)

  • 이재헌
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.12 no.4
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    • pp.926-933
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    • 1988
  • A Numerical method has been introduced to handle a pressure-based boundary condition of the incompressible viscous flow field. This method, based on SIMPLER algorithm, has been applied to analyze the flow characteristics within a two-dimensional duct of two-exit, as an example. From this, it is possible to determine the ratio of flow rate through two exits imposed on different static pressure. In order to check the validity of the present method, calculated velocity at the boundary imposed on pressure condition by the use of present method has been transferred to the velocity boundary condition of the conventional numerical method workable only with the velocity-based boundary condition. It is found that the calculated boundary pressure from conventional method are almost identical to those endowed originally. Present method, therefore will be widely applicable to the practical situations specified by the pressure-based boundary condition rather than the velocity one.

Calculation of three-dimensional boundary layer near the plane of symmetry of an automobile configuration (자동차 중앙대칭단면 부근의 3차원경계층 계산)

  • 최장섭;최도형;박승오
    • Journal of the korean Society of Automotive Engineers
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    • v.10 no.2
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    • pp.61-69
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    • 1988
  • The finite-difference three-dimensional boundary layer procedure of Chang and Patel is modified and applied to solve the boundary layer development on the automobile surface. The inviscid pressure distribution needed to solve the boundary layer equations is obtained by using a low order panel method. The plane of symmetry boundary layer exhibits the strong streamline divergence up to the midbody and convergence thereafter. The streamline divergence in front of the windshield helps the boundary layer to overcome the sever adverse pressure gradient and avoid the separation. The relaxation of the pressure right after the top of the wind-shield, on the other hand, makes the overly thinned boundary layer to readjust and prompts the streamlines to converge into the symmetry plane before the external streamlines do. The three-dimensional characteristics are less apparent after the midbody and the boundary layer is similar to that of the two-dimensional flow. The results of the off-plane-of-symmetry boundary layer are also presented.

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Wall Pressure Fluctuations of the Boundary Layer Flow at the Nose of and Axisymmetric Body (축대칭 물체 선단에서 발생하는 경계층 내 벽면 변동 압력에 관한 연구)

  • 신구균;홍진숙;김상윤;김상렬;박규철
    • Journal of KSNVE
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    • v.10 no.4
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    • pp.602-609
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    • 2000
  • When an axisymmetric body moves through air the boundary layer near the stagnation region remains laminar and subsequently it goes through transition to turbulent. The experimental investigation described in this paper concerns the characteristics of wall pressure fluctuations at the initial stage of boundary layer flow including transition. Flush-mounted microphones are used to measure the wall pressure fluctuations at the transition and turbulent boundary layer region of a blunt axisymmetric body in the low noise wind tunnel. It if found from this study that the wall pressure fluctuations in the transition region is higher than that in the turbulent region.

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Effects of boundary layer and liquid viscosity and compressible air on sloshing characteristics

  • Zou, Chang-Fang;Wang, De-Yu;Cai, Zhong-Hua
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.7 no.4
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    • pp.670-690
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    • 2015
  • In this paper, numerical investigations for tank sloshing, based on commercial CFD package FLUENT, are performed to study effects of boundary layer grid, liquid viscosity and compressible air on sloshing pressure, wave height and rising time of impact pressure. Also, sloshing experiments for liquids of different viscosity are carried out to validate the numerical results. Through comparison of numerical and experimental results, a computational model including boundary layer grid can predict the sloshing pressure more accurately. Energy dissipation due to viscous friction leads to reduction of sloshing pressure and wave elevation. Sloshing pressure is also reduced because of cushion effect of compressible air. Due to high viscosity damping effect and compressible air effect, the rising time of impact pressure becomes longer. It is also found that liquid viscosity and compressible air influence distribution of dynamic pressure along the vertical tank wall.

Pressure Correction Method and Slip Boundary Conditions for Microflows (미소유동 해석을 위한 압력수정기법 및 미끄럼 경계조건)

  • Choi, Hyung-Il;Maeng, Joo-Sung;Lee, Do-Hyung
    • Proceedings of the KSME Conference
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    • 2001.06e
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    • pp.430-435
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    • 2001
  • This paper introduces a pressure correction method for microflow computation. Conventional CFD methods with no slip boundary condition fail to predict the rarefaction effect of the wall when simulating gas microflows in the slip-flow regime. Pressure correction method with an appropriate slip boundary condition is an efficient tool in analyzing microscale flows. The present unstructured SIMPLE algorithm adopts both the classical Maxwell boundary condition and Langmuir boundary condition proposed by Myong. The simulation results of microchannel flows show that the proposed method has an effective predictive capability for microscale flows.

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Investigation of Burst Pressures in PWR Primary Pressure Boundary Components

  • Namgung, Ihn;Giang, Nguyen Hoang
    • Nuclear Engineering and Technology
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    • v.48 no.1
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    • pp.236-245
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    • 2016
  • In a reactor coolant system of a nuclear power plant (NPP), an overpressure protection system keeps pressure in the loop within 110% of design pressure. However if the system does not work properly, pressure in the loop could elevate hugely in a short time. It would be seriously disastrous if a weak point in the pressure boundary component bursts and releases radioactive material within the containment; and it may lead to a leak outside the containment. In this study, a gross deformation that leads to a burst of pressure boundary components was investigated. Major components in the primary pressure boundary that is structurally important were selected based on structural mechanics, then, they were used to study the burst pressure of components by finite element method (FEM) analysis and by number of closed forms of theoretical relations. The burst pressure was also used as a metric of design optimization. It revealed which component was the weakest and which component had the highest margin to bursting failure. This information is valuable in severe accident progression prediction. The burst pressures of APR-1400, AP1000 and VVER-1000 reactor coolant systems were evaluated and compared to give relative margins of safety.