• 대한기계학회논문집B
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• 제33권2호
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• pp.107-115
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• 2009

A Computational study was carried out in order to investigate the aerodynamic characteristics of circular cylinder moving near the wavy wall at a low Reynolds number of 50. Lattice Boltzmann method was used to simulate the flow field and immersed boundary method was combined to represent the moving cylinder and wavy wall regardless of the constructed grid in the domain. The aerodynamics characteristics of the cylinder moving near the wavy wall were represented by the comparing the lifting coefficients with various altitudes (H/D) and wave length and amplitudes of wavy wall. It indicated that the twice of increasing-decreasing variations of lifting coefficient are obtained while the cylinder moves near the wavy wall. The first variation is obtained where the cylinder locates near the peak of the wavy wall. Another variation occurs when the distance to the wavy wall becomes longer after passing the peak. It was also classified that three different patterns of relation between the lifting and drag coefficient of the cylinder. However, the classification is limited to the case of the same order of altitude, amplitude and wave length of the wavy wall.

• 대한기계학회논문집
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• 제18권6호
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• pp.1582-1589
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• 1994

The characteristics Prandt1-Meyer expansion of supersonic flow with condensation through a wavy wall in a channel are investigated by experiment and numerical direct marching method of characteristics. In the present study, for the case of moist air flow in the type of indraft supersonic wind tunnel, the dependency of location of formation and reflection of the oblique shock wave generated by the wavy wall and the distribution of flow properties, on the specific humidity and temperature at the entrance of wavy wall and the attack angle of the wavy wall to the main stream is clarified by schlieren photograph, distribution of static pressure and Mach number, and plots of numerical results. Also, we confirm that the wavy wall plays an important key role in the formation of oblique shock wave, and that the effect of condensation on the flow field appears apparently.

• Journal of Mechanical Science and Technology
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• 제15권4호
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• pp.492-499
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• 2001

The characteristics of Prand시-Meyer expansion of supersonic flow with condensation along a wavy wall in a channel are investigated by means of experiments and numerical analyses. Experiments are carried out for the case of moist air flow in an intermittent indraft supersonic wind tunnel. The flow fields are visualized by a Schlieren system and the distributions of static pressure along the upper wavy wall are measured by a scanning valve system with pressure transducers. In numerical analyses, the distributions of streamlines, Mach lines, iso-pressure lines, and iso-mass fractions of liquid are obtained by the two-dimensional direct marching method of characteristics. The effects of stagnation temperature, absolute humidity, and attack angle of the upper wavy wall on the generation and the locations of generation and reflection of an oblique shock wave are clarified. Futhermore, it is confirmed that the wavy wall plays an important role in the generation of an oblique shock wave and that the effect of condensation on the flow fields is apparent.

• 한국전산유체공학회지
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• 제16권2호
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• pp.49-55
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• 2011

Turbulent flows with wavy wall are simulated using Residual-based Variational Multiscale Method (RB-VMS) which is proposed by Bazilves et al(2007) as new Large Eddy Simulation methodology. Incompressible Navier-Stokes equations are integrated using Isogeometric analysis which adopt the basis function as NURBS. The Reynolds number is 6760 based on the bulk velocity and averaged channel height. And the amplitude (${\alpha}/{\lambda}$) of wavy wall is 0.05. The computational domain is $2{\lambda}{\times}1.05{\lambda}{\times}{\lambda}$ in the streamwise, wall normal and spanwise direction. Mean quantities and turbulent statistics near wavy wall are compared with DNS results of Cherukat et al.(1998). The predicted results show good agreement with reference data.

• 한국전산유체공학회지
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• 제17권2호
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• pp.93-99
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• 2012

The present study focuses on the case of developing flow with in a channel containing a long array of sinusoidal waves (2a/${\lambda}$=0.1, ${\lambda}$=h, ${\lambda}$ is the wavelength, 2a is the wave height, h is the mean channel depth) at the bottom wall. The Reynolds number defined with channel height, h and the mean velocity, U, is Re=6,700. The channel is sufficiently long such that transition is completed and the flow is fully developed over the downstream half of the channel. For the case of an incoming steady flow with no resolved turbulence, the instantaneous flow fields in the transition region are characterized by the formation of arrays of highly-organized large-scale hairpin vortices whose dimensions scale with that of the roughness elements. The paper explains the mechanism for the formation of these arrays of hairpin vortices and shows these eddies play the primary role in the formation of the large-scale streaks of high and low velocity over the wavy wall region. The presence of resolved turbulence in the incoming flow, reduces the streamwise distance needed for the streaks to develop over the wavy region, but does not affect qualitatively the transition process. In the fully-developed region, isolated and trains of large-scale hairpins play an important role in the dynamics of the streaks over the wavy wall.

• 대한기계학회논문집
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• 제16권10호
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• pp.1990-1997
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• 1992

본 연구에서는 미소진폭의 파형벽을 가진 유로내에 응축성 기체인 습공기가 초음속으로 흐르는 경우의 유동에 대하여 정체점에서의 상대습도와 온도의 변화에 따 른 유동장내의 상태량의 변화와 경사충격파의 거동 등을 2차원 수직해석을 통하여 규 명하였다.

• 대한기계학회논문집
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• 제18권2호
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• pp.424-431
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• 1994

The characteristics of supersonic flow with condensation along a wavy wall of a small Smplitude in a channel is investigated experimentally and numerically. In the present study for the case of supersonic moist air flow, the dependency of location of reflection of oblique shock wave generated by the wavy wall, and the distributions of flow properties in the flow field, on the stagnation relative humidity and temperature is clarified by the plots of streamline, iso-Mach number and iso-flow properties of numerical result and the schlieren photographs of experiment. And. experimental and numerical results are in good agreement.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2352-2356
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• 2008

Heat transfer and performance characteristics have been investigated for a rectangular wavy duct with dimple or protrusion arrays. The test duct was 15mm in height and 105mm wide. The print diameter of the dimple/protrusion wall was 12.99mm and the depth/height of the dimple/protrusion was 3.75mm. Local heat transfer coefficients on the dimple/protrusion wall were measured using a transient TLC technique. The Reynolds number was varied from 3,000 to 10,000. For the wavy duct tested in this study, adverse static pressure characteristics occurred at turning region of the wavy duct due to secondary flows. For the wavy duct with protrusion array, higher heat transfer enhancement level of 7.4 times than smooth straight case in maximum was obtained at low Reynolds number due to the high heat transfer enhancement by vortex flows. Also, the protrusion array increased the performance level of 3.0 at low Reynolds number of 3,000.

• 설비공학논문집
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• 제15권10호
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• pp.809-820
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• 2003

The present study investigates effects of flow velocity on the convective heat/mass transfer characteristics in wavy ducts of a primary surface heat exchanger application. Local heat/mass transfer coefficients on the wavy duct sidewall are determined by using a naphthalene sublimation technique. The flow visualization technique is used to understand the overall flow structures inside the duct. The aspect ratio and corrugation angle of the wavy duct is fixed at 7.3 and 145$^{\circ}$ respectively, and the Reynolds numbers, based on the duct hydraulic diameter, vary from 100 to 5,000. The results show that there exist complex secondary flows and transfer processes resulting in non-uniform distributions of the heat/mass transfer coefficients on the duct side walls. At low Re (Re<1000), relatively high heat/mass transfer regions like cell shape appear on both pressure and suction side wall due to the secondary vortex flows called Taylor-Gortler vortices perpendicular to the main flow direction. However, at high Re (Re>1000), these secondary flow cells disappear and boundary layer type flow characteristics are observed on pressure side wall and high heat/mass transfer region by the flow reattachment appears on the suction side wall. The average heat/mass transfer coefficients are higher than those of the smooth circular duct due to the secondary flows inside wavy duct. And also friction factors are about two times greater than those of the smooth circular duct.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2267-2272
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• 2007

The present study investigates the two dimensional flow and heat/mass transfer characteristics of wavy duct with various corrugation angles. For the heat/mass transfer coefficients, a naphthalene sublimation technique is used. Numerical analysis and wall pressure measurement show detailed two dimensional flow features. The corrugation angles change from 145$^{\circ}$ to 100$^{\circ}$. The operating Reynolds numbers based on the duct hydraulic diameter vary from 700 to 3,000. The duct aspect ratio maintains 7.3. On the pressure wall, strong flow mixing enhances heat/mass transfer coefficients at the front position. In addition, the rear side of pressure wall, the near of peak, is affected by the acceleration and the shedding of main flow. On the suction wall, however, flow separation and reattachment lead to the valley and the peak of heat/mass transfer coefficient. Also, highly increasing boundary layer at the suction wall affects the decrease of heat/masst transfer. As decreasing corrugation angles, the spanwise average Sherwood number increases and the peak or the valley positions of the local Sherwood number are varied.