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CONTENTS
Volume 11, Number 5, September 2008
 

Abstract
An experimental investigation of the flow over the rectangular body located in close proximity to a ground board was reported using the particle image velocimetry (PIV) technique. The present experiments were conducted in a closed-loop open surface water channel with the Reynolds number, ReH?=?1.2?104 based on the model height. In addition to the PIV measurements, flow visualization studies were also carried out. The PIV technique provided instantaneous and time-averaged velocity vectors map, vorticity contours, streamline topology and turbulent quantities at various locations in the near wake. In the vertical symmetry plane, the upperbody flow is separated from the sharp top leading edge of the model and formed a large reverse flow region on the upper surface of the model. The flow structure downstream of the model has asymmetric double vortices. In the horizontal symmetry plane, identical separated flow regions occur on both vertical side walls and a pair of primary recirculatory bubbles dominates the wake region.

Key Words
ground vehicle aerodynamics; PIV, rectangular body; wake flow.

Address
Cukurova University, Faculty of Engineering and Architecture, Department of Mechanical Engineering, 01330 Adana, Turkey

Abstract
This paper considers internal pressure fluctuations for a range of building volumes and dominant wall opening areas. The study recognizes that the air flow in and out of the dominant opening in the envelope generates Helmholtz resonance, which can amplify the internal pressure fluctuations compared to the external pressure, at the opening. Numerical methods were used to estimate fluctuating standard deviation and peak (i.e. design) internal pressures from full-scale measured external pressures. The ratios of standard deviation and peak internal pressures to the external pressures at a dominant windward wall opening of area, AW are presented in terms of the non-dimensional opening size to volume parameter, , where as is the speed of sound, is the mean wind speed at the top of the building and VIe is the effective internal volume. The standard deviation of internal pressure exceeds the external pressures at the opening, for greater than about 0.75, showing increasing amplification with increasing . The peak internal pressure can be expected to exceed the peak external pressure at the opening by 10% to 50%, for greater than about 5. A dominant leeward wall opening also produces similar fluctuating internal pressure characteristics.

Key Words
low-rise building; internal pressure; dominant opening; volume; Helmholtz resonance.

Address
John D. Ginger; Cyclone Testing Station, James Cook University, Townsville, Queensland, 4811, Australia
John D. Holmes; JDH Consulting, Mentone, Victoria, 3194 Australia
Gregory A. Kopp; Boundary Layer Wind Tunnel Laboratory, University of Western Ontario, London, N6A 5B9, Canada

Abstract
An experimental investigation has been conducted to determine the effectiveness of base shield plates in reducing the drag of a rough circular cylinder in a cross flow at Reynolds numbers in the range 3?104??Re??10.5?104. Three model configurations were investigated and compared: a plane cylinder (PC), a cylinder with a splitter plate (MC1) and a cylinder fitted with base shield plates (MC2). Each configuration was studied in the sub and supercritical flow regimes. The chord of the plates, L, ranged from 0.22 to 1.50D and the cavity width, G, between the plates was in the range from 0 to 0.93D. It is recognized that base shield plates can be employed more effectively than splitter plates to reduce the aerodynamic drag of circular cylinders in both the sub- and supercritical flow regimes. For subcritical flow regime, one can get 53% and 24% drag reductions for the MC2 and MC1 models with L/D?=?1.0, respectively, compared with the PC model. For supercritical flow regime however, the corresponding drag reductions are 38% and 7%. Keywords:

Key Words
drag reduction; circular cylinder; wake splitter plates; base shield plates; base cavity; separation.

Address
Department of Civil Engineering, University of Jordan, Amman, Jordan

Abstract
A design procedure of stabilizing cable is proposed using buffeting analysis to stabilize the seesaw-like motion of the free cantilevered structure of a cable-stayed bridge during its construction. The bridge examined is a composite cable-stayed bridge having a main span length of 500?m. Based on the buffeting analysis, the stress in bare structure exceeded the allowable limit and a set of stabilizing cable was planned to mitigate the responses. The most efficient positions of the hold-down stabilizing cables were numerically investigated by means of an FE-based buffeting analysis and the required dimensions and pretension of the stabilizing cables were also calculated. The proposed stabilizing measure would be expected to secure the aerodynamic safety of a cantilevered structure under construction with considerable mitigation of buffeting responses.

Key Words
buffeting; stabilizing cable; cable-stayed bridge; construction; design.

Address
Sung-Won Choi; DM engineering, Bangii-dong, Songpa-ku, Seoul, 138-050, Korea
Ho-Kyung Kim; Department of Civil Engineering, Mokpo National University, Muan-gun, Jeonnam, 534-729, Korea

Abstract
A wind tunnel study has been carried out to determine the influence of spacing between buildings on wind characteristics above rural and suburban type of terrain. Experiments were performed for two types of buildings, three-floor family houses and five-floor apartment buildings. The atmospheric boundary layer (ABL) models were generated by means of the Counihan method using a castellated barrier wall, vortex generators and a fetch of roughness elements. A hot wire anemometry system was applied for measurement of mean velocity and velocity fluctuations. The mean velocity profiles are in good agreement with the power law for exponent values from ??=?0.15 to ??=?0.24, which is acceptable for the representation of the rural and suburban ABL, respectively. Effects of the spacing density among buildings on wind characteristics range from the ground up to 0.6?. As the spacing becomes smaller, the mean flow is slowed down, whilst, simultaneously, the turbulence intensity and absolute values of the Reynolds stress increase due to the increased friction between the surface and the air flow. This results in a higher ventilation efficiency as the increased retardation of horizontal flow simultaneously accompanies an intensified vertical transfer of momentum.

Key Words
wind characteristics; spacing between buildings; wind tunnel simulation.

Address
Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Ivana 5, HR-10000 Zagreb, Croatia
Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA


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