• Title/Summary/Keyword: Boundary Layer

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Control of Shock-Wave/Bound-Layer Interactions by Bleed

  • Shih, T.I.P.
    • International Journal of Fluid Machinery and Systems
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    • v.1 no.1
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    • pp.24-32
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    • 2008
  • Bleeding away a part of the boundary layer next to the wall is an effective method for controlling boundary-layer distortions from incident shock waves or curvature in geometry. When the boundary-layer flow is supersonic, the physics of bleeding with and without an incident shock wave is more complicated than just the removal of lower momentum fluid next to the wall. This paper reviews CFD studies of shock-wave/boundary-layer interactions on a flat plate with bleed into a plenum through a single hole, three holes in tandem, and four rows of staggered holes in which the simulation resolves not just the flow above the plate, but also the flow through each bleed hole and the plenum. The focus is on understanding the nature of the bleed process.

Strengthening Robustness within the Boundary Layer by Incorporating Adaptive Control

  • Park, Gee-yong;Yoon, Ji-sup;Park, Byung-suk;Hong, Dong-hee;Kim, Young-hwan
    • 제어로봇시스템학회:학술대회논문집
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    • pp.48.1-48
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    • 2002
  • The method of endowing the controller with the strengthened robustness within the boundary layer is presented for controlling the uncertain nonlinear systems in which the variations of the uncertainties are slow. From this controller, the width of the boundary layer where the robust control input is smoothened out can be given by an appropriate value but a better control performance within the boundary layer can be achieved without the control chattering because the role of adaptive control is to compensate for the uncovered portions of the robust control occurred from the continuous approximation within the boundary layer.

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Numerical Simulation of MIT Flapping Foil Experiment : Unsteady Flow Characteristics (MIT 요동 익형의 수치해석 : 비정상 유동 특성)

  • Bae Sang Su;Kang Dong Jin;Kim Jae Won
    • 한국전산유체공학회:학술대회논문집
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    • pp.133-140
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    • 1998
  • A Navier-Stokes code based on a unstructured finite volume method is used to simulate the MIT flapping foil experiment. A low Reynolds number $k-{\varepsilon}$ turbulence model is used to close the Reynolds averaged Navier-Stokes equations. Computations are carried out for a domain involving two flapping foils and a downstream hydrofoil. The computational domain is meshed with unstructured quadrilateral elements, partly structured. Numerical solutions show good agreement with experiment. Unsteadiness inside boundary layer is entrained when a unsteady vortex impinge on the blade surface. It shoves that local peak value inside the boundary layer and also local minimum near the edge of boundary layer as it developes along the blade surface. The unsteadiness inside the boundary layer is almost isolated from the free stream unsteadiness and being convected at local boundary layer speed, less than the free stream value.

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A study on the early stage of a transitional boundary layer and far field noise using a large eddy simulation technique (큰 에디 모사 기법을 이용한 초기 천이 경계층 유동 및 방사 소음 해석)

  • Choe, Myeong-Ryeol;Choe, Hae-Cheon;Gang, Sin-Hyeong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.6
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    • pp.779-792
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    • 1997
  • Flow characteristics are numerically investigated when a packet of waves consisting of a Tollmien-Schlichting wave and a pair of Squire waves evolves in a flat-plate laminar boundary layer using a large eddy simulation with a dynamic subgrid-scale model. Characteristics of early stage transitional boundary layer flow such as the .LAMBDA. vortex, variation of the skin friction and backscatter are predicted. Smagorinsky constants and the eddy viscosity obtained from the dynamic subgrid-scale model significantly change as the flow evolves. Far Field noise radiated from the transitional boundary layer shows the dipole and quadrupole characteristics owing to the wall shear stress and the Reynolds stresses, respectively.

ANALYSIS OF TURBULENT BOUNDARY LAYER FLOWS USING A TIME MARCHING METHOD (시간 전진법을 이용한 난류 경계층 유동의 해석)

  • Gong, H.;Lee, S.
    • Journal of computational fluids engineering
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    • v.20 no.1
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    • pp.32-38
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    • 2015
  • A 3-dimensional compressible turbulent boundary layer solver has been developed. A time marching method is used to integrate the turbulent boundary layer equations. While the direct integration of the boundary layer equations is performed for unseparated flow regions, the inverse integration is performed for separated flow regions. The program is verified for flows that have analytical solutions or other numerical results. The solver will be merged with an Euler solver for viscous-inviscid interaction.

EFFECTS OF TURBULENCE MODEL AND EDDY VISCOSITY IN SHOCK-WAVE / BOUNDARY LAYER INTERACTION (충격파 경계층 상호작용에서 난류모델 및 난류점성의 효과)

  • Jeon, Sang Eon;Park, Soo Hyung;Byun, Yung Hwan
    • Journal of computational fluids engineering
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    • v.18 no.2
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    • pp.56-65
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    • 2013
  • Two compression ramp problems and an impinging shock problem are computed to investigate influence of turbulence models and eddy viscosity on the shock-wave / boundary layer interaction. A Navier-Stokes boundary layer generation code was applied to the generation of inflow boundary conditions. Computational results are validated well with the experimental data and effects of turbulence models are investigated. It is shown that the behavior of turbulence (eddy) viscosity directly affects both the extent of the separation and shock-wave positions over the separation.

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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Numerical Simulation of MIT Flapping Foil Experiment (MIT 요동 익형의 수치해석)

  • Kang, Dong-Jin;Bae, Sang-Soo
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.6
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    • pp.777-784
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    • 2000
  • A Navier-Stokes code based on an unstructured finite volume method is used to simulate the MIT flapping foil experiment. A low Reynolds number ${\kappa}-{\varepsilon}$ turbulence model is used to close the Reynolds averaged Navier-Stokes equations. Computations are carried out for the whole experimental domain involving two flapping foils and a downstream hydrofoil. The computational domain is meshed with unstructured quadrilateral elements, partly structured. Numerical solutions show good agreement with experiment. The first harmonics of the velocity in the boundary layer shows local peak value inside the boundary layer and also local minimum near the edge of boundary layer. It is intensified as it develops along the blade surface. This is shown to be caused as the unsteadiness inside the boundary layer is being convected at a speed less than the free stream value. It is also shown that there is negligible mixing of the unsteadiness between the boundary layer and the free stream.

Modeling of Boundary Layer using Atmospheric Boundary Layer Wind Tunnel of UCD (UCD 대기경계층 풍동을 이용한 경계층 형성)

  • White, Bruce R.;Kim, Bong-Hwan;Kim, Dae-Seong
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.11 no.2
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    • pp.118-124
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    • 2012
  • The simulation of the air flow over models in atmospheric boundary layer wind tunnel is a research region based on advanced scientific technologies imposed by the necessity of studying the turbulent fluid dynamics in the proximity of the Earth's surface. In this study, the atmospheric boundary layer wind tunnel of UCD is used, the mean velocities are measured by augmentation devices such as roughness blocks and spires. The experimental results of mean velocity profile are well fitted with the value of power law.

Characteristics of Nocturnal Boundary Layer Observed in Kyungpook Province (경북지역에서 관측된 야간 대기경계층의 특성)

  • Byung-Hyuk Kwon
    • Journal of Environmental Science International
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    • v.10 no.5
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    • pp.329-336
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    • 2001
  • Characgcteristics of nocturnal boundary layer(NBL) were analyzed by the upper-air observations data using with the airsonde and pilot balloons from 1994 to 1999 in Kyungpook province. The automate weather boundary layer can become stably stratified when the surface is cooler than the air. Stable nocturnal boundary layer height were estimated from the top of surface stable layer where the vertical gradient of temperature and mixing ratio tend to zero or negative. The depth of the stable nocturnal boundary layer depended largely on the thermal effect rather than the wind effect at nighttime. The NBL was more developed on the land than on the coastal region. The stability index (bulk Richardson number) showed that the NBL was stable when the wind was weak and the vertical gradient of the temperature was strong. The heat budget in the NBL was studied by considering the effect of the radiative and the cooled by both the longwave radiative flux and the divergence of the heat flux, while NBL under the cloudy sky the longwave radiative flux played a role of the warming. It was noted that the heat was not conserved in both cases. To complete the heat budget in the NBL the warming/cooling by advection and subsidence must be considered.

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