• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1863-1868
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• 2004

The present study concerns a computational study of fully developed laminar flow of a Newtonian fluid through an eccentric annulus with a combined bulk axial flow and inner cylinder rotation. This study considers the identical flow geometry as in the calculation of Escudier et $al.^{(3)}$ An unexpected feature of the calculations for eccentricity ${\varepsilon}$)0.7 is the appearance of a second peak in the axial velocity, located in the narrowing gap. The distribution of the axial component of the surface shear stress has a maximum in the narrowing gap and a minimum in the widening gap.

• 대한기계학회논문집B
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• 제25권6호
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• pp.786-798
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• 2001

This paper describes the phenomena of wake-induced transition of the boundary layers on a NACA0012 airfoil using measured phase-averaged data. Especially, the phase-averaged wall shear stresses are reasonably evaluated using the principle of Computational Preston Tube Method. Due to the passing wake, the turbulent patch is generated in the laminar boundary layer on the airfoil and the boundary layer becomes temporarily transitional. The patches propagate downstream with less speed than free-stream velocity and merge with each other at further down stream station, and the boundary layer becomes more transitional. The generation of turbulent patch at the leading edge of the airfoil mainly depends on velocity defects and turbulent intensity profiles of passing wakes. However, the growth and merging of turbulent patches depend on local streamwise pressure gradients as well as characteristics of turbulent patches. In this transition process, the present experimental data show very similar features to the previous numerical and experimental studies. It is confirmed that the two phase-averaged mean velocity dips appear in the outer region of transitional boundary layer for each passing cycle. Relatively high values of the phase-averaged turbulent fluctuations in the outer region indicate the possibility that breakdown occurs in the outer layer not near the wall.

• 한국산학기술학회논문지
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• 제19권7호
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• pp.72-80
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• 2018

과학 및 공학 분야 등에서 유한체적법등과 같은 전산해석방법은 비약적으로 발전하여 주로 대학 연구실 및 기업 등에서 활용하고 있었으나 최근에는 대학의 교육과정에서도 전산해석방법이 도입되고 있다. 이것을 계기로 공학대학의 기계공학과등에서 전산유체동역학이 학부 3학년 또는 4학년에 개설되고 있다. 일반적으로 전산유체동역학에서 다루는 수치해석 예제는 상용 전산유체동역학 소프트웨어 회사에서 개발한 예제이다. 따라서 학부 학생들은 저학년에서 학습한 유체역학의 이론적 해와 전산유체동역학 강의에서 학습하는 수치해석 해를 서로 비교할 수 없는 상황이 되고 있다. 따라서 본 연구에서는 유체동역학의 고전적인 해석 대상인인 정상 상태의 수평 원관 층류 유동의 이론적 배경을 설명한 뒤 ANSYS FLUENT를 이용하여 정상 상태의 수평 원관 층류 유동에 대한 수치해석 해를 구하여 이론적 해와 수치해석 해를 서로 비교하여 학생들의 전산유체동역학에 대한 개념을 확실히 다짐으로서 학생들의 현장적응능력을 높였으며 해당 강좌에 대한 강의 평가 결과 학생들이 전산유체동역학에 대한 이해력과 tutorial에 대한 만족도가 매우 높았다.

• 대한조선학회논문집
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• 제58권4호
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• pp.243-252
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• 2021

The present study aims to investigate the interaction of a wire-type turbulence stimulator and the laminar boundary layer on a flat plate by flow field measurement. For the towing tank tests, a one-dimensional Laser Doppler Velocimetry (LDV) attached on a two-axis traverse was used to measure the streamwise velocity component of the boundary layer flow in zero pressure gradient, disturbed by a turbulence stimulator. The wire diameter was 0.5 and 1.0 mm according to the recommended procedures and guidelines suggested by the International Towing Tank Conference. Turbulence development by the stimulator was identified by the skin friction coefficient, mean and Root Mean Square (RMS) of the streamwise velocity. The laminar boundary layer with the absence of the wire-type stimulator was similar to the Blasius solution and previous experimental results. By the stimulator, the mean and RMS of the streamwise velocity were increased near the wall, showing typical features of the fully developed turbulent boundary layer. The critical Reynolds number was reduced from 2.7×10⁵ to 1.0×10⁵ by the disturbances caused by the wire. As the wire diameter and the roughness Reynolds number (Rek) increased, the disturbances by the stimulator increased RMS of the streamwise velocity than turbulent boundary layer.