Wind flow characteristics and their effects on low-rise buildings



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Texas Tech University


Two fundamental flow phenomena, the separation bubble (SB) and conical vortex, over the roof (flat and rectangular) of the Texas Tech test building are studied in terms of flow characteristics and pressure-generating mechanisms. Major fmdings contribute to understanding the mechanisms of pressure generation and the roles of turbulence and other properties of the incident wind in loading effects.

Much of the debate on wind-tunnel simulation priority in the wind engineering community has failed to distinguish the different effects the incident wind has on two types of quantities: single events, e.g., minimum (peak) pressures, and statistics, such as the mean and the rms pressures. The turbulence intensities, reflecting the gust structure and the directional fluctuations of the free-stream wind, might bear significant influences collectively on the pressure statistics. It is the intensity of individual longitudinal gusts (as well as the incident wind angles) that decides the data-run-wise peak-pressure coefficients on the roof corner, while the peak-pressure coefficients associated with the SB are governed by the lateral directional fluctuation in the incident wind. Proper simulation of the incident wind profile (boundary layer type) is probably the most important single input in the wind - structure interaction process.

The separation bubble, having a mean reattachment-point approximately 10 ft from the leading edge, is oblong and elongated in the horizontal direction. Pressure distribution on the roof surface is intimately related to the structure of the SB. Conditional sampling technique indicates that the wind flow associated with strong suctions is highly threedimensional. Introduction of the non-conventional pressure coefficient makes it possible to isolate the effect of wind speed from that of the wind direction on pressure generation. The mechanism of peak-pressure generation associated with the SB is governed by directional fluctuations of incident wind. Primary peaks of pressure coefficient (conventional) are often an outcome of combined wind gust and fast direction fluctuation. Non-Gaussian-pressure zone along the short roof-axis is found to extend about 15 ft from the leading edge. This dimension is comparable to the stream-wise overall size of the vortex circulation and to the height of the test building (13 ft).