• Wind and Structures
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• v.15 no.6
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• pp.463-480
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• 2012

The effects of Reynolds number (Re), freestream turbulence intensity (Tu) and integral length scale (${\Lambda}$) on the drag coefficient ($C_d$) of a circular cylinder in cross flow were experimentally studied for $6.45{\times}10^3$ < Re < $1.82{\times}10^4$. With the help of orificed plates, Tu was fixed at approximately 0.5%, 5%, 7% and 9% and the normalized integral length scale (L/D) was varied from 0.35 to 1.05. Our turbulent results confirmed the general trend of decreasing $C_d$ with increasing Tu. The effectiveness of Tu in reducing $C_d$ is found to lessen with increasing ${\Lambda}$/D. Most interestingly, freestream turbulence of low Tu (${\approx}5%$) and large ${\Lambda}$/D (${\approx}1.05$) can increase the $C_d$ above the corresponding smooth flow value.

• Coupled systems mechanics
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• v.3 no.1
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• pp.27-52
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• 2014

For landfill monitoring and aftercare, long-term prognoses of emission and deformation behaviour are required. Landfills may be considered as heterogeneous porous soil-like structures, in which flow and transport processes of gases and liquids interact with local material degradation and mechanical deformation of the solid skeleton. Therefore, in the framework of continuous porous media mechanics a model is developed that permits the investigation of coupled mechanical, hydraulical and biochemical processes in municipal solid waste landfills.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.09a
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• pp.550-551
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• 2005

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.3
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• pp.207-215
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• 2008

The heat/mass transfer characteristics on the plane tip surface of a high-turning first-stage turbine rotor blade has been investigated by employing the naphthalene sublimation technique. At the Reynolds number of $2.09{\times}10^5$, heat/mass transfer coefficients are measured for the tip gap height-to-chord ratio, h/c, of 2.0% at turbulence levels of Tu = 0.3 and 14.7%. A tip-surface flow visualization is also performed for h/c = 2.0% at Tu = 0.3%. The results show that there exists a strong flow separation/re-attachment process, which results in severe local thermal load along the pressure-side corner, and a pair of vortices named "tip gap vortices" in this study is identified along the pressure and suction-side tip corners near the leading edge. The loci and subsequent development of the pressure- and suction-side tip gap vortices are discussed in detail. The combustor-level high inlet turbulence, which increases the tip-surface heat/mass transfer, provides more uniform thermal-load distribution.

• Journal of the Korean Society of Visualization
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• v.11 no.2
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• pp.27-33
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• 2013

The inlet flow of centrifugal blower were quantitatively visualized using particle image velocimetry. Because the centrifugal blower system is one of the key parts of EV battery cooling system, the quantitative information of flow field of centrifugal blower is important to design and optimize the cooling system. Two types of inlet parts were used in this study. One is the straight inlet and the other is a bended one. The results showed the flow asymmetry exists in the straight model due to the pressure difference in the blower. In case of the bended one, the separation bubble and the increase of head loss appeared compared with the straight model.

• Journal of Information Processing Systems
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• v.19 no.1
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• pp.130-138
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• 2023

The traffic flow in an urban area is affected by the date, weather, and regional traffic flow. The existing methods are weak to model the dynamic road network features, which results in inadequate long-term prediction performance. To solve the problems regarding insufficient capacity for dynamic modeling of road network structures and insufficient mining of dynamic spatio-temporal features. In this study, we propose a novel traffic flow prediction framework called shared spatio-temporal attention convolution optimization network (SSTACON). The shared spatio-temporal attention convolution layer shares a spatio-temporal attention structure, that is designed to extract dynamic spatio-temporal features from historical traffic conditions. Subsequently, the graph optimization module is used to model the dynamic road network structure. The experimental evaluation conducted on two datasets shows that the proposed method outperforms state-of-the-art methods at all time intervals.

• Journal of the Korean Society of Visualization
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• v.12 no.1
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• pp.25-29
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• 2014

The outlet flow of the centrifugal blower were quantitatively visualized using particle image velocimetry. Because the centrifugal blower is one of the key parts of electric vehicle battery cooling system, the quantitative information of centrifugal blower is necessary to design and optimize the cooling system. The effect of different inlet flow condition to the outlet flow was investigated in this study. Two different inlet ducts were used. One is the straight inlet and the other is a bended one. The results clearly showed the outlet flow asymmetry in both inlet ducts. When the blower has the bended inlet, the flow rate decreases due to the increase of the head loss.

• Journal of the Korean Society of Visualization
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• v.8 no.3
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• pp.35-40
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• 2010

We have investigated different radial temperature gradient effect on the stability of Taylor-Couette flow. The radius ratio and aspect ratio of the model was 0.825 and 48, respectively. Two heating exchangers were used for generating different temperature gradient along the radial direction. The change of flow regime in the Taylor-Couette flow was studied by increasing the Reynolds number. The results showed that: as Gr is increased in helical vortex flow regime, the vortices with the same direction of convection flow increased in size, and the vortex moving velocity also increased. It is also shown that the presence of temperature gradient obviously increased the flow instability when the Richardson number is larger than 0.0045.

• Journal of Advanced Marine Engineering and Technology
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• v.20 no.5
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• pp.58-67
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• 1996

In the present study, the pressure distribution, wall shear stress distribution and friction factor of developing turbulent pulsating flows are investigated theoretically and experimentally in the entrance region of a square duct. The pressure distribution for turbulent pulsating flows are in good agreement with the theoretical values. The time-averaged pressure gradients of the turbulent pulsating flows show the same tendency as those of turbulent steady flows as the time-averged Reynolds number $(Re_{ta})$ increase. Mean shear stresses in the turbulent pulsating flow increase more in the inlet flow region than in the fully developed flow region and approach to almost constant value in the fully developed flow region. In the turbulent pulsating flow, the friction factor of the quasi-steady state flow $({\lambda}_{q, tu})$ follow friction factor's law in turbulent steady flow. The entrance length of the turbulent pulsating flow is not influenced by the time-averaged Reynolds number $(Re_{ta})$ and it is about 40 times as large as the hydraulic diameter.

• Journal of the Korean Society of Visualization
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• v.21 no.1
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• pp.47-56
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• 2023

Bubble condensation, which involves the interaction of bubbles within the subcooled liquid flow, plays an important role in the effective control of thermal devices. In this study, numerical simulations are performed using a VOF (Volume of Fluid) model to investigate the effect of tube diameter on bubble condensation. As the tube diameter decreases, condensation bubbles persist for a long time and disappear at a higher position. It is observed that for small tube diameters, the heat transfer coefficients of condensation bubbles, which is a quantitative parameter of condensation rate, are smaller than those for large tube diameters. When the tube diameter is small, the subcooled liquid around the condensing bubble is locally participated in the condensation of the bubble to fill the reduced volume of the bubble due to the generation of a backflow in the narrow space between the bubble and the wall, so that the heat transfer coefficient decreases.