• Title/Summary/Keyword: Boundary Layer

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

  • Lee, Keun-Hyoung
    • Journal of Mechanical Science and Technology
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    • v.16 no.12
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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.

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

  • 서봉록;김시영
    • Journal of Advanced Marine Engineering and Technology
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    • v.10 no.4
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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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Generation of a Turbulent Boundary Layer Using LES (LES를 이용한 난류경계층의 생성에 관한 연구)

  • Lim, Hee-Chang
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.8
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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.

Second-Order Wave Resistance Calculation of Thin-Ship (얇은 배에 대한 고차 조파저항 계산)

  • Shin-Hyoung,Kang
    • Bulletin of the Society of Naval Architects of Korea
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    • v.16 no.3
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    • pp.35-47
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    • 1979
  • Wave resistance of a parabolic thin ship, with its boundary layer and wake taken into account, was calculated up to second order. In addition to the double-model source distribution on the centerplane, image sources of the wave potential were calculated to keep the body introduced boundary condition undisturbed. Boundary layer and wake effects on the wave-making resistance were included by generating an irrotational flow which matches that exterior to the boundary layer and wake. For this purpose, the boundary layer and wake were calculated. The wave resistance refined with second-order corrections are found to be very important for wave resistance calculations even at moderate Froude numbers($Fr=0.2{\sim}0.3$). Wave-potential corrections are dominate around the bow. On the other hand, Viscosity plays and important role at the stern with its boundary layer and wake development.

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Study on the Turbulent Boundary Layer Disturbed by a Triangular Prism near the Wall (벽근방의 3각주에 의하여 교란받는 난류경계층에 관한 연구)

  • Sim, W.G.;Lee, K.J.;Cho, Y.C.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.3 no.3
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    • pp.161-167
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    • 1991
  • This paper presents the results of some measurement of the fluctuating velocity field in the turbulent boundary layer disturbed by a triangular prism and discusses the discovery of the disturbed boundary layer. A prism of height 8mm was used for experiments. The streamwise location of the prism was fixed at 1200mm downstream from the leading edge and the space between the prism center and the wall was set at three different values, 6, 15 and 33.5mm. The results show that the near-wall region of the disturbed boundary layer recovers original state much more quickly than the outer region. In the case h=6mm the recovery is faster than the other cases. Moreover, it was found that peak of fluctuating velocities moves outwards somewhat rapidly with increasing ${\times}$ mainly due to the turbulent diffusion of the fluctuating velocity.

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Axisymmetric Thick Turbulent Boundary Layer Around a Rotating Body of Revolution (회전하는 회전체 주위의 축대칭 두꺼운 난류경계층 연구)

  • Shin-Hyoung,Kang;Jung-Ho,Hwang
    • Bulletin of the Society of Naval Architects of Korea
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    • v.23 no.1
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    • pp.13-22
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    • 1986
  • Axisymmetric turbulent thick boundary layers on a rotating body of revolution are calculated numerically in the paper. Richardson number is introduced to the mixing length to take account of swirl effects on Reynolds stresses. Interactions of the boundary layer and the external potential flow are included by adding the displacement thickness of boundary layers on the original body. Pressure distributions on the body surface are estimated by integrating normal momentum equation across the boundary layer. A model is designed and tested in the wind tunnel. Mean velocities are measured. Through the present study, swirl effects on the thick axisymmetric boundary layer development are considerable in comparison with those of non-totating cases. Rotational motion generally increase boundary layer thickness, axial skin friction coefficients, and form drags. Circumferential flow can be reversed to induce negative skin friction when the section area is reduced.

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Error Reduction of Sliding Mode Control Using Sigmoid-Type Nonlinear Interpolation in the Boundary Layer

  • Kim, Yoo-Kyung;Jeon, Gi-Joon
    • International Journal of Control, Automation, and Systems
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    • v.2 no.4
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    • pp.523-529
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    • 2004
  • Sliding mode control with nonlinear interpolation in the boundary layer is proposed. A modified sigmoid function is used for nonlinear interpolation in the boundary layer and its parameter is tuned by a fuzzy controller. The fuzzy controller that takes both the sliding variable and a measure of chattering as its inputs tunes the parameter of the modified sigmoid function. Owing to the decreased thickness of the boundary layer and the tuned parameter, the proposed method has superior tracking performance than the conventional linear interpolation method.

Mach 6 Tests of Scramjet Engine with Boundary-Layer Bleeding and Two-Staged Injection

  • Kodera, Masatoshi;Tomioka, Sadatake;Kobayashi, Kan;Kanda, Takeshi;Mitani, Tohru
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.26-33
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    • 2004
  • In this study, a boundary-layer bleeding and a two-staged fuel injection were applied to a scramjet engine for suppressing unstart transition and improving the thrust performance under Mach 6 flight conditions. With the boundary-layer bleeding, the engine could operate without unstart transition around at the fuel equivalence ratio of unity ($\Phi$ = 1). The thrust increment from the no fuel condition (dF) increased to 2460 N, which was about 1.4 times as large as that of the case without the bleeding and maximum in our Mach 6 tests. It was confirmed that the boundary-layer bleeding suppressed the separation during the engine operation. The two-staged fuel injection was less effective for improving the thrust performance com-pared with the single-staged one with the bleeding at Mach 6.

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Experimental Study on Measuring the Intermittency in the Transitional Boundary Layer (천이경계층에서의 간헐도 측정에 관한 실험적 연구)

  • 임효재;안재용;백성구;정명균
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.15 no.1
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    • pp.9-18
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    • 2003
  • An experimental study was performed to investigate the turbulence intermittency measuring methods across the boundary layer in the transition region. A single type hot-wire probe was used to measure instantaneous streamwise velocities in laminar, transitional and turbulent boundary layer To estimate wall shear stresses on the flat plate, near wall mean velocities are applied to the principle of CPM. Distribution of intermittency factor is obtained by dual-slope method and compared to the results of four methods,$\'{u},\;\{U}$, TERA and M-TERA method. In these methods, M-TERA shows a good agreement in the near wall region. However, the result of M-TERA method shows that intermittency factor is underestimated in the outer part and outside of the boundary layer and the dimensional constant of M-TERA method should be changed appropriately depending on measuring point.

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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    • v.18 no.1
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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.