Partha P. Sarkar

Flow visualization of conical vortices on flat roofs with simultaneous surface pressure measurement

Abstract Wind tunnel and full-scale pressure studies of flow over low-rise buildings have repeatedly shown that on the roof, the largest mean and peak suction values are observed for taps beneath the conical “delta-wing type” corner vortices that occur for oblique winds. To better understand the flow mechanism which produces these negative pressure coefficients, a flow visualization study of conical vortex behaviour was performed in the wind tunnels of Colorado State University (CSU) and at full scale at Texas Tech University (TTU). The mean position and size of the vortices as a function of wind direction is presented. Pressures were also simultaneously measured beneath the vortex visualization plane in the wind tunnel for the worst case wind directions. These pressure profiles were correlated with the digitally enhanced images of the vortex flow. The greatest suction was found to follow directly beneath the moving vortex core. For smooth flow, the magnitude of the suction beneath the core was seen to vary inversely with the vortex size, but no relationship between vortex size and suction could be seen for turbulent flow.

Mean and fluctuating wind loads on rough and smooth parabolic domes

Abstract Simultaneous pressure measurements have been obtained on rough and smooth parabolic domes in simulated atmospheric boundary layer flow. Mean and fluctuating pressure distributions compare favorably with earlier studies for similar shape and Reynolds number. The effect of surface roughness is to reduce suctions over the apex of the dome and increase suctions in the wake region on the leeward face. The consequence for mean and fluctuating overall loads is reduced uplift but increased drag for rougher surfaces. Correlation analysis of the fluctuating pressures reveals that the first two eigenvectors account for approximately 60% of the fluctuating pressure energy and follow the mean pressure coefficient and its gradient with respect to horizontal wind direction as predicted by the quasi-steady theory. Overall base shear and uplift forces on the domes can be well approximated by this theory.

The effect of section model details on aeroelastic parameters

In the five decades since the flutter-induced failure of the Tacoma Narrows bridge, understanding of the physical mechanisms at work has advanced. On the one hand, numerical modeling capability, most notably through the finite element method, and developments in the theory of random vibration have contributed; on the other hand, wind tunnel modeling remains of central importance relative to long-span bridges. The results presented herein indicate the critical dependence of the aeroelastic behavior on even minor details such as a deck railing. These particular observations have important general implications for both 2-D and 3-D modeling. The paper examines a particular problem of details in some depth to emphasize its importance.

Flow visualization and measurement on the roof of the Texas Tech building

Flow visualization and flow measurement on the roof of the Texas Tech Building are performed in this study. It mainly explores visualization techniques applied to full scale and discusses the results of flow measurements within the separation bubble. The shape of the separation bubble along one axis of the building has been characterized by an intermittency factor. Preliminary observations of the dynamics of the separation bubble are made based upon visualization records.

The Texas Tech project for dissemination of wind engineering research and curriculum via electronic media

Abstract The importance of transferring the wind engineering research into curriculum and practice has been the focus of much attention in the recent past. Also, many Universities are exploring ways to enhance their existing curriculum for both on-campus students and distance education. With the emergence of software and computer hardware specifically designed for multimedia-based presentations and the constantly improving conditions for learning via the Internet, it is now possible to achieve these goals more effectively than ever before. In this paper, three separate efforts at Texas Tech University are described; integrating wind engineering research to the existing curriculum, developing a wind engineering course for distance education, and devising a method for fast dissemination of wind engineering research and curriculum, all involving different forms of electronic media.

Wind-induced loads on metal edge flashings

This paper reports the results of wind-tunnel and full-scale measurements of wind pressure on metal edge flashings. The wind-tunnel tests provide useful information on failure mechanisms of the flashing-cleat system. The wind pressure data collected at the Texas Tech University Wind Engineering Research Field Laboratory (WERFL) building represent the effects of the natural wind. Finite element analyses using pressure data from the full-scale tests calculate stresses at critical sections of the edge flashing and pull-out forces on the fasteners. The results suggest outward acting fastener pull-out forces, even when the wind is blowing toward the face of the edge flashing (windward wind).