• Wind and Structures
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• v.12 no.1
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• pp.21-47
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• 2009

The logarithmic form for turbulent flow analysis guarantees the positivity of the turbulence variables as ${\kappa}$ and ${\varepsilon}$ of the ${\kappa}-{\varepsilon}$ model by using the natural logarithm of these variables. In the present study, the logarithmic form is incorporated into the finite element solution procedure for the unsteady turbulent flow analysis. A backward facing step flow using the standard ${\kappa}-{\varepsilon}$ model and a flow around a 2D square cylinder using the modified ${\kappa}-{\varepsilon}$ model (the Kato-Launder model) are simulated. These results show that the logarithmic form effectively keeps adequate balance of turbulence variables and makes the analysis stable during transient or unsteady processes.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.779-782
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• 2002

We examine the problem in which porous/viscoelastic compliant thin plates are subject to pressure fluctuations under transitional or turbulent boundary layer. Measurements are presented of the frequency spectra of the near-field pressure and radiated sound by compliant surface. A porous plate consisting of 5mm thick, open-cell foam with fabric covering and a viscoelastic painted plate of 1mm thick over an acoustic board of 4m thick were placed over a rigid surface in an anechoic wind tunnel. Streamwise velocity and wall pressure measurements were shown to highly attenuate the convective wall pressure energy when the convective wavenumber ($k_{ch}$) was 3.0 or more. The sound source localization on the compliant walls is applied to the measurement of radiated sound by using an acoustic mirror system.

• Wind and Structures
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• v.30 no.2
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• pp.133-140
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• 2020

In this paper, critical fluid velocity and frequency of laminated pipe conveying fluid are presented. Each layer of the pipe is reinforced by functionally graded carbon nanotubes (FG-CNTs). The internal fluid is assumed turbulent and the induced forces are calculated by momentum equations. The pipe is resting on viscoelastic foundation with spring, shear and damping constants. The motion equations are derived based on classical shell theory and energy method. Differential quadrature method (DQM) is used for solution and obtaining the critical fluid velocity. The effects of volume percent and distribution of CNT, boundary condition, lamina layer number, length to radius ration of pipe, viscoelastic medium and fluid velocity are shown on the critical fluid velocity. Results show that with increasing the lamina layer number, the critical fluid velocity increases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.3
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• pp.294-301
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• 2003

We examine a problem in which porous/viscoelastic compliant thin plates are subject to pressure fluctuations under transitional or turbulent boundary layer. Measurements are presented of the frequency spectra of the near-field pressure and radiated sound by compliant surface. A porous plate consisting of 5mm thick. open-cell foam with fabric covering and a viscoelastic-painted plate of 1mm thick over an acoustic board of 4mm thick were placed over a rigid surface in an anechoic wind tunnel. Streamwise velocity and wall pressure measurements were shown to highly attenuate the convective wall pressure energy when the convective wavenumber (k$_{c}$h) was 3.0 or more. The sound source localization on the compliant walls is applied to the measurement of radiated sound by using an acoustic mirror system.

• Wind and Structures
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• v.5 no.1
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• pp.15-24
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• 2002

This paper reports the numerical calculations of uniform turbulent shear flow around a square cylinder. The predictions are obtained by solving the two-dimensional unsteady Navier-Stokes equations in a finite volume technique. The turbulent fluctuations are simulated by the standard $k-{\varepsilon}$ model and one of its variant which takes care of the realizability constraint in order to suppress the excessive generation of turbulence in a stagnation condition. It has been found that the Strouhal number and the mean drag coefficient are almost unaffected by the shear parameter but the mean lift coefficient is increased. The present predictions are compared with available experimental data.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.16 no.1
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• pp.74-80
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• 1987

Turbulent convective heat transfer phenomenon which occur around the evaporator section of heat pump were analyzed experimentally. For this purpose a special wind tunnel and a heat pump system were designed and fabricated. Evaporator section was installed perpendicular to air flow direction and part of the evaporator was made of a glass tube for visual observation. The velocity distribution, turbulent intensity and temperature distribution were measured by hot wire technique and thermocouples. An experimental correlation for the convective heat transfer coefficient was obtained and the result is somewhat higher than the value calculated from Hilpert equation. The difference in two equations is believed to be due to the boning effect inside the evaporator tube.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• v.4 no.2
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• pp.117-125
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• 2000

A series of simulations were carried out to test the accuracy of a CFD (Computational Fluid Dynamics) model for flow and dispersion problems around buildings. The basic equations involved are Reynolds-averaged Navier-Stokes equations. Two different cases were selected to estimate the accuracy of a CFD model. Case 1 adopted Euler equations, which are obtained by neglecting the viscous fluxes, which can be closed by the $textsc{k}$-$\varepsilon$model for a turbulent close problem. The results of both cases were compared with wind tunnel data. The results for Case 2 were closer to the wind both cases were compared with wind tunnel data. The results for Case 2 were closer to the wind tunnel data than Case 1. Accordingly, this indicates that the inclusion of viscous fluxes in a CFD model is required for the simulation of flow and 야spersion around buildings.

• Wind and Structures
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• v.13 no.4
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• pp.327-346
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• 2010

During the past decade, many electrical transmission tower structures have failed during downburst events. This study is a part of a research program aimed to understand the behaviour of transmission lines under such localized wind events. The present study focuses on the assessment of the dynamic behaviour of the line conductors under downburst loading. A non-linear numerical model, accounting for large deformations and the effect of pretension loading, is developed and used to predict the natural frequencies and mode shapes of conductors at various loading stages. A turbulence signal is extracted from a set of full-scale data. It is added to the mean component of the downburst wind field previously evaluated from a CFD analysis. Dynamic analysis is performed using various downburst configurations. The study reveals that the response is affected by the background component, while the resonant component turns to be negligible due large aerodynamic damping of the conductors.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.740-745
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• 2000

Effects of porous fences on the wind erosion of sand particles from a triangular pile were investigated experimentally. The porous fence and sand pile were installed in a simulated atmospheric boundary layer. The mean velocity and turbulent intensity profiles measured at the sand pile location were well fitted to the atmospheric boundary layer over the open terrain. Particle motion was visualized to see the motion of windblown sand particles qualitatively. In addition, the threshold velocity were measured using a light sensitive video camera with varying the fence porosity ${\varepsilon}$. As a result, various types of particle motion were observed according to the fence porosity. The porous wind fence having porosity ${\varepsilon}=30%$ was revealed to have the maximum threshold velocity, indicating good shelter effect for abating windblown dust particles.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.2
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• pp.118-124
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• 2012

The simulation of the air flow over models in atmospheric boundary layer wind tunnel is a research region based on advanced scientific technologies imposed by the necessity of studying the turbulent fluid dynamics in the proximity of the Earth's surface. In this study, the atmospheric boundary layer wind tunnel of UCD is used, the mean velocities are measured by augmentation devices such as roughness blocks and spires. The experimental results of mean velocity profile are well fitted with the value of power law.