Simplified Wind Flow Model for the Estimation of Aerodynamic Effects on Small Structures

Abstract

The reliable measurement of pressures on low-rise buildings in the atmospheric boundary layer (ABL) flow remains a challenge, as hasbeenshownbythelargediscrepanciesamongresultsobtainedindifferentwindtunnelfacilitiesoreveninthesamewindtunnel.Twomajor causes of the discrepancies are the difficulty of simulating large-scale, low-frequency turbulent fluctuations uniformly across laboratories and the small scale of models in typical civil engineering wind tunnels. To address these issues, it was proposed that a simplified flow be used in laboratory simulations,rather thana conventionalABL flow.In thesimplified flowthe referencemeanwind speedislarger thanthemean wind speed of the ABL flow, and the low-frequency fluctuations present in the ABL flow are suppressed; that is, the peak energy of the missing low- frequency fluctuations is supplied in the simplified flow by the increment in the mean wind speed, which may be regarded as a flow fluctuation with zero frequency. High-frequency turbulent fluctuations, which typically affect flow reattachment, are approximately the same in the ABL and the simplified flow. Because, over small distances, low-frequency fluctuations are highly coherent spatially for small low-rise buildings with dimensions of up to approximately 20 m (e.g., single-family residential homes), the peak aerodynamic effects of the two flows may be hypothesized to be approximately the same. Preliminary experimental results obtained in University of Western Ontario's ABL wind tunnel facility and Florida International University's small-scale Wall of Wind facility are shown to support this hypothesis. The use of the proposed simplified flow is currently being tested by the authors for application to computational wind engineering (CWE) applications. Such use eliminatestheneedtosimulatethelowerfrequency fluctuationsoftheboundarylayer flowandthusmakesitpossibletoachievepracticalCWE calculations, and it is advantageous in experiments from the points of view of measurement accuracy, model scaling, repeatability of the simulations, and computational efficiency. DOI: 10.1061/(ASCE)EM.1943-7889.0000508. © 2013 American Society of Civil Engineers. CE Database subject headings: Boundary layers; Wind loads; Low-rise buildings; Wind tunnels. Author keywords: Atmospheric boundary layer; Computational wind engineering; Flow modeling; Low-rise buildings; Wind engineering; Wind tunnel tests.