• International Journal of High-Rise Buildings
• /
• v.8 no.4
• /
• pp.255-264
• /
• 2019

This paper describes large eddy simulation of wind pressures on a square cylinder in a uniform flow and a high-rise building immersed in an atmospheric turbulent boundary layer. For the atmospheric boundary layer case, the inflow turbulence is generated by a numerical wind tunnel. In the numerical simulation, particular attention is devoted to the performance of an auto hexahedral non-structural mesh. Both simulations are performed for three grid systems: an auto hexahedral non-structured grid, a structured Cartesian grid and a non-structured triangular prism grid, and for three grid numbers. The present study shows that the auto hexahedral unstructured mesh achieves the best simulation results for wind pressures on the square cylinder and the high-rise building. When the grid number is sufficiently large, the differences among the results obtained from the three investigated grid systems are not significant. However, the advantage of the auto hexahedral unstructured mesh becomes clear when the grid number decreases, because it enables a balanced distribution of orthogonal grids. The results described in this paper demonstrate that the auto hexahedral non-structured mesh has good potential applicability to simulation of urban flows.

• Journal of Korean Society of Environmental Engineers
• /
• v.39 no.12
• /
• pp.706-713
• /
• 2017

This study compared and analyzed the water treatment efficiency and the applicability of water treatment plant using the existing Mechanical Rapid-Mixer by introducing the Non-powered Vortex Mixer to the domestic water treatment plant. For this study, fluid flow characteristics and head loss of a Non-powered Vortex Mixer are calculated by Computational Fluid Dynamics (CFD)respectively. The head loss rate inside the mixer was 11.30% when the inflow velocity was 0.5 m/sec, 16.27% at 0.6 m/sec and 21.44% at 0.7 m/sec, the head loss rapidly increased at the optimal velocity of 0.5 m/sec. For the inflow velocity of 0.5 m/sec, the turbulent intensity at the inlet was 2.37% and at the outlet was 7.83%, so there was sufficient mixing strength for the particulate matter and the coagulant. The result of the water quality of the treatment plants with the inflow velocity of 0.38 m/sec that was operated in three years after replacing all 12 units of the existing Rapid-Mixer with the Non-powered Mixer met the standards. Hence, it is possible to reduce the energy consumption of 64,143 ~ 65,306 kWh/year since the Rapid-Mixer is replaced by the Non-powered Vortex Mixer.

• Journal of the Society of Naval Architects of Korea
• /
• v.44 no.2 s.152
• /
• pp.64-73
• /
• 2007

Turbulent flows around yacht sails were calculated to access the applicability of CFD for yacht design. Multi-block grid system was generated by using Gridgen package and Fluent was used to calculate flows around two sail system. A 30ft class sailing yacht designed and tested by KRISO was chosen. The interference effect between main and jib sails was analyzed. Pressure distribution on the sails was obtained and the center of effort was estimated. It was found that the jib angle affects the flow phenomena around a main sail due to the change of inflow angle. The location of center of effort is much different from the empirical formula based on a simple geometrical consideration. The calculated results are compared with the previous numerical and experimental results. Both CFD results are similar, but there are some discrepancies with experimental data. However, it is certain that CFD can be a very useful tool for yacht design.

• Journal of computational fluids engineering
• /
• v.6 no.2
• /
• pp.22-31
• /
• 2001

The two-dimensional unsteady incompressible viscous flow behind rectangular bluff bodies between two parallel plates was analyzed numerically. The steady state flow and the vortex flow behind rectangular bluff bodies in the channel were investigated for two regimes i.e., the laminar(Re = 100, 300, 500) and the turbulent flows(Re = 10⁴∼10/sup 6/). The vortex shedding was generated by a physical disturbance(6%) numerically imposed at the rear of the bluff bodies for a short time. It was observed that the perturbed flow became periodic after a transient period. And in the case of unsteady inflow, the sinusoidal pulsatile flow was applied as the inlet condition in the turbulent flow of Reynolds number of 1.0×10/sup 5/. FLUENT code was employed to solve the problems. The power-law scheme was used to get stable linearized equations and the PISO algorithm was applied to finding the solution of them.

• Wind and Structures
• /
• v.13 no.6
• /
• pp.529-556
• /
• 2010

This paper investigates the correlation of wind characteristics monitored on a cable-stayed bridge. Total five anemoscopes are implemented into the bridge. Two out of 5 anemoscopes in inflow and two out of 5 anemoscopes in wake-flow along the longitudinal direction of the bridge are installed. Four anemoscopes are respectively distributed at two cross-sections. Another anemoscope is installed at the top of the tower. The correlation of mean wind speed and direction, power spectral density, the turbulent intensity and integral length of wind in flow at two cross-sections are investigated. In addition, considering the non-stationary characteristics of wind, the spatial correlation in time-frequency is analyzed using wavelet transform and different phenomenon from those obtained through FFT is observed. The time-frequency analysis further indicates that intermittence, coherence structures and self-similar structures are distinctly observed from fluctuant wind. The flow characteristics around the bridge deck at two positions are also investigated using the field measurement. The results indicate that the mean wind speed decrease when the flow passing through the deck, but the turbulence intensity become much larger and the turbulence integral lengths become much smaller compared with those of inflow. The relationship of RMS (root mean square) of wake-flow and the mean wind speed of inflow is approximately linear. The special structures of wake-flow in time-frequency domain are also analyzed using wavelet transform, which aids to reveal the forming process of wake-flow.

• 유체기계공업학회:학술대회논문집
• /
• 2002.12a
• /
• pp.116-122
• /
• 2002

It is addressed that the turbulent broadband sound power from a sirocco fan can be modeled by the trailing edge noise. The trailing edge noise is usually influenced by inflow turbulenca separation, and boundary layer thickness on the blade. The design parameters such as solidity (c/s) and stagger angle are specified to predict performance and noise level because the separation and slip velocity are strongly affected by them along with the flow coefficient. This paper reports the effects of the stagger angle upon the trailing edge noise for various trailing edge shapes. It is believed that the serrated trailing edge provides break-up mechanism for organized convecting vortices, thereby reduce the overall noise level for every case of stagger angle.

• 한국전산유체공학회:학술대회논문집
• /
• 2005.10a
• /
• pp.239-243
• /
• 2005

Fully three-dimensional Large Eddy Simulation calculations of the flow past 2D cavity are conducted to study the purging of neutrally buoyant or dense miscible contaminants introduced instantaneously inside the cavity. The length to depth ratio(L/D) is 2 and Reynolds number based on the depth is 3,360. Fully developed turbulent inflow are fed at the inlet from precursor simulation of channel flow. Mean flow pattern and unsteady features are investigated based on the experimental data of Pereira and Sousa. From the study of mass exchange processes, it is found that the mechanism of removal of the contaminant is very different between the non-buoyant and buoyant cases. In the buoyant case, internal wave motion which interacts with a strong cavity vortex is dominant in the ejection mechanism of the contaminants.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.11b
• /
• pp.652-657
• /
• 2002

It is addressed that the turbulent broadband sound power from a sirocco fan can be modeled by the trailing edge noise. The trailing edge noise is usually influenced by inflow turbulence, separation and boundary layer on the blade. The design parameters such as solidity(c/s) and stagger angle are specified to predict performance and noise level because the separation and slip velocity are strongly affected by them along with the flow coefficient. This paper reports the effects of the stagger angle upon the trailing edge noise for various trailing edge shapes. It is believed that the serrated trailing edge provides break-up mechanism for organized convecting vortices, thereby reduce the overall noise level.

• The KSFM Journal of Fluid Machinery
• /
• v.6 no.3 s.20
• /
• pp.7-14
• /
• 2003

It is addressed that the turbulent broadband sound power from a sirocco fan can be modeled by the trailing edge noise. The trailing edge noise is usually influenced by inflow turbulence, separation, and boundary layer thickness on the blade. The design parameters such as solidity (c/s) and stagger angle are specified to predict performance and noise level because the separation and slip velocity are strongly affected by them along with the flow coefficient. This paper reports the effects of the stagger angle upon the trailing edge noise for various trailing edge shapes. It is believed that the serrated trailing edge provides break-up mechanism for organized convecting vortices, thereby reduce the overall noise level for every case of stagger angle.

• 유체기계공업학회:학술대회논문집
• /
• 2000.12a
• /
• pp.137-142
• /
• 2000

The turbulent broadband sound power from a forward curved bladed fan can be modeled by the trailing edge noise. The trailing edge noise is usually influenced by inflow turbulence, separation, and boundary layer on the blade. This paper reports the effects of the solidity (C/s) and the stagger angles upon the trailing edge noise with respect to the trailing edge shapes of circular-arc cambered blade of multi-bladed fan, and discusses the major physical mechanism of reduced noise lot the circular trailing-edged case.