• 제목/요약/키워드: Boundary Layer

검색결과 2,593건 처리시간 0.03초

Control of Boundary Layer Flow Transition via Distributed Reduced-Order Controller

  • Lee, Keun-Hyoung
    • Journal of Mechanical Science and Technology
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    • 제16권12호
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    • pp.1561-1575
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    • 2002
  • A reduced-order linear feedback controller, which is used to control the linear disturbance in two-dimensional plane Poiseuille flow, is applied to a boundary layer flow for stability control. Using model reduction and linear-quadratic-Gaussian/loop-transfer-recovery control synthesis, a distributed controller is designed from the linearized two-dimensional Navier-Stokes equations. This reduced-order controller, requiring only the wall-shear information, is shown to effectively suppress the linear disturbance in boundary layer flow under the uncertainty of Reynolds number. The controller also suppresses the nonlinear disturbance in the boundary layer flow, which would lead to unstable flow regime without control. The flow is relaminarized in the long run. Other effects of the controller on the flow are also discussed.

정상상태인 박용 TP620 익형의 경계층 특성 연구 (A study on the boundary layer characteristics of TP620 hydrofoil in the steady state)

  • 서봉록;김시영
    • Journal of Advanced Marine Engineering and Technology
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    • 제10권4호
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    • pp.50-56
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    • 1986
  • This report deals with a study on the boundary layer characteristics of TP620 hydrofoil in the steady state by using two dimensional boundary layer theory. On the basis of complex velocity and laminar and turbulent boundary layer theory, the author attempts to know some tendency by evaluating the performance characteristic values of TP620 hydrofoil working in a uniform flow. In deriving characteristic values, he calculates numerically velocity, momentum thickness, skin friction coefficient, shape factor, and displacement thickness on the TP620 hydrofoil working at each attack angle in a uniform flow. Applying this present numerical calculation using Thwaites' and Head's method, the results of boundary layer on the hydrofoil are shown to be influenced by surface velocity and attack angle.

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LES를 이용한 난류경계층의 생성에 관한 연구 (Generation of a Turbulent Boundary Layer Using LES)

  • 임희창
    • 대한기계학회논문집B
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    • 제31권8호
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    • pp.680-687
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    • 2007
  • The paper presents a numerical simulation of flow of a turbulent boundary layer, representing a typical wind environment and matching a series of wind tunnel observations. The simulations are carried out at a Reynolds number of 20,000, based on the velocity U at a pseudo-height h, and large enough that the flow be effectively Reynolds number independent. Some wall models are proposed for the LES(Large Eddy Simulation) of the turbulent boundary layer over a rough surface. The Jenson number, $J=h/z_0$, based on the roughness length $z_0$, is 600 to match the wind tunnel data. The computational mesh is uniform with a spacing of h/32, as this aids rapid convergence of the multigrid solver, and the governing equations are discretised using second order finite differences within a parallel multiblock environment. The results presented include the comparison between wind tunnel measurements and LES computations of the turbulent boundary layer over rough surface.

Prediction of Transonic Buffet Onset for a Supercritical Airfoil with Shock-Boundary Layer Interactions Using Navier-Stokes Solver

  • Chung, Injae
    • International Journal of Aeronautical and Space Sciences
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    • 제18권1호
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    • pp.1-7
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    • 2017
  • To predict the transonic buffet onset for a supercritical airfoil with shock-boundary layer interactions, a practical steady approach has been proposed. In this study, it is assumed that the airfoil flow is steady even when buffet onset occurs. Steady Navier-Stokes computations are performed on the supercritical airfoil. Using the aerodynamic parameters calculated from Navier-Stokes solver, various steady approaches for predicting buffet onset are discussed. Among the various steady approaches considered in this study, Thomas' criterion based on Navier-Stokes computation has shown to be the most appropriate indicator of identifying the buffet onset for a supercritical airfoil with shock-boundary layer interactions. Good agreements have been obtained compared with the results of unsteady transonic wind tunnel tests. The present method is shown to be reliable and useful for transonic buffet onset for a supercritical airfoil with shock-boundary layer interactions in terms of practical engineering viewpoint.

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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    • 제어로봇시스템학회 2002년도 ICCAS
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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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MIT 요동 익형의 수치해석 : 비정상 유동 특성 (Numerical Simulation of MIT Flapping Foil Experiment : Unsteady Flow Characteristics)

  • 배상수;강동진;김재원
    • 한국전산유체공학회:학술대회논문집
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    • 한국전산유체공학회 1998년도 추계 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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큰 에디 모사 기법을 이용한 초기 천이 경계층 유동 및 방사 소음 해석 (A study on the early stage of a transitional boundary layer and far field noise using a large eddy simulation technique)

  • 최명렬;최해천;강신형
    • 대한기계학회논문집B
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    • 제21권6호
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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.

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

  • 공효준;이승수
    • 한국전산유체공학회지
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    • 제20권1호
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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.

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

  • 신구균;홍진숙;김상윤;김상렬;박규철
    • 소음진동
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    • 제10권4호
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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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