• 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.

• 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.

• 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.

• 대한기계학회논문집B
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• 제24권6호
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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.

• 대한설비공학회지:설비저널
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• 제14권4호
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• pp.293-299
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• 1985

This paper describes an economical prediction procedure for heat transfer phenomenon through a channel containing an abrupt asymmetric expansion in flow cross-seetional area. Numerical solutions for the flow field are obtained by the finite difference numerical method applied to the modified boundary layer equations. Modified boundary energy equation is used to analyze heat transfer as modified boundary momentum equation. Predictions of the method compare very favorable with exprimental data. Results of this study by modified boundary layer equation are as follows : 1. The computation time required for the scheme is at least an order of magnitude less than for the numerical solution of the full Navier-stokes and Energy eguations. 2. In laminar flow, the maximum heat transfer occurs downstream of the reattachment point.

• 한국산학기술학회논문지
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• 제13권12호
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• pp.5655-5660
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• 2012

본 연구의 목적은 경계층 해석법을 이용하여 고효율 열교환기 설계를 위한 이론적 접근법을 제시하고 기존 열교환기에 많이 사용되고 있는 사각 평판 핀과 이를 대체할 수 있는 원형 평판 핀에 대하여 경계층 형성과 간섭에 대하여 설명하고 속도 및 온도 경계층 성장에 따른 열전달계수의 변화를 나타내고자 한다. 더불어 한 개의 핀에서의 유동은 외부유동으로 간주할 수 있으나 다수의 핀 사이의 유동은 내부유동으로 간주하였고 이론적인 결과를 도출하였다. 결과적으로 열교환기의 고효율화 및 컴팩트화를 실현하기 위하여 경계층 간섭을 회피할 수 있는 방안을 이론적으로 제시하였고, 이러한 관점에서 원형 평판 핀이 사각 평판 핀에 비하여 열전달성능이 우수함을 알 수 있었다.

• 대한토목학회논문집
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• 제13권2호
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• pp.267-277
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• 1993

본 논문에서는 유한요소법을 2차원 난류경계층에 적용하였으며, 점성유체의 시간의존 비압축성 운동을 시간과 압력장(場)에서 Navier-Stokes방정식과 vorticity방정식을 이용하여 정식 화하였다. 수치계산방법은 Galerkin방법에 기초하였으며, 난류 경계층의 eddy kinematic viscosity에 대해서는 Prandtl의 혼합거리이론을 도입하였다. 난류 경계층에서 파동에 의한 임의 저면에서 저질의 이동을 수치계산하였다. 유한 요소법에 의해 얻어진 결과는 진동흐름에 의한 경계층과 파동에 의한 경계층에서의 특성의 차이를 분명히 하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.506-511
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• 2001

This paper presents how redevelopment of the boundary layer in a backward-facing step flow is affected by boundary conditions imposed on velocity at the inlet, top and exit of the flow. A two-dimensional, laminar, incompressible flow over a backward-facing step with an open top boundary has been computed by using numerical methods of second-order time and spatial accuracy and a fractional-step method that guarantees a divergence-free velocity field at all time. The inlet velocity profile above the step is of Blasius type. Along the top boundary, shear-tree and Dirichlet conditions on the streamwise velocity were considered and at the exit fully-developed and convective boundary conditions were examined. (The vertical velocity at all boundaries were assumed to be zero explicitly or implicitly.) From the computed flow fields, the reattachment on the bottom side of shear layer separated from the tip of the step and succeeding redevelopment of the boundary layer were investigated.

• International Journal of Ocean System Engineering
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• 제3권3호
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• pp.111-115
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• 2013

Blasius equation describes the boundary layer formed over a flat plate inside a fluid and this equation is solved numerically by the method of moments which is a type of weighted residual methods. Compared to the traditionally used Runge - Kutta Method, Method of Moments propose a direct solution to Blasius Equation which makes it easier to solve. The obtained solutions show good agreement with the results found in literature and this study aims to demonstrate the power of the method.

• 한국해안해양공학회지
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• 제10권2호
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• pp.93-99
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• 1998

타원형 유한차분모형에서 개방 경계조건으로 포물선 근사식과 스폰지층 경계를 사용하여 모형의 개량을 도모하였다. 수치기법은 GCG(Generalized conjugate gradient)기법을 사용하였고 구형해저실험에서 포물형 근사식을 사용하여 부적절한 반사파를 상당 부분 제거할 수 있었다. 스폰지층 경계의 경우 2파장 이상의 스폰지층을 사용할 때 포물형 근사식과 유사한 결과를 얻을 수있었다. 직사각형 항만에 대한 실험을 통하여 임의 형상의 대상 해역에도 쉽게 모형을 적용할 수 있음을 확인하였다.