Excerpt from An Efficient Large Eddy Simulation Algorithm for Computational Wind Engineering: Application to Surface Pressure Computations on a Single Building, August, 1999

All demonstrate the capability of the methods by comparison either with wind-tunnel re sults or with full-scale measurements. The latter are difficult to obtain, may be unrepeatable and usually have large uncertainties. Wind-tunnel measurements, on the other hand, arecontrolled and more reproducible, and are commonly used for cwe assessment and valida tions. Wind-tunnel tests conducted by Flachsbart at the Goettingen Aerodynamics Research Establishment in 1932 were the first to point out the differences between aerodynamic pres sures on building models tested in uniform, smooth flow on the one hand and in shear flow on the other; typical results are reproduced in Wind Effects on Structures, [6] p. 173. Test ing in shear flow, simulating with various degrees of success the atmospheric boundary layer flow, became routine in engineering practice only in the 1960's. At that time Baines [7] reported a classic set of measurements of mean pressures in a wind tunnel under both smooth uniform flow and shear flow. Recently, in a systematic joint effort under the aegis of the Architectural Institute of Japan (au) computational results obtained by three universities and nine industrial institutes were compared with wind tunnel measurements conducted under test conditions specified in careful detail.

Shear flow is associated with mechanical turbulence, which has been shown experimen tally to influence the flow-body interaction. The magnitude of this influence varies depending upon the situation at hand. For example, consider a building located in a city center. To simulate correctly wind effects on that building it is necessary to model not only the building itself but also the buildings surrounding it. The signature turbulence of those buildings is likely to dominate the incoming flow turbulence, that is, the turbulence in the undisturbed flow at a sufficiently large distance upwind of the set of buildings of interest (the signature turbulence of a body is the turbulence generated by the interaction of the incoming flow with that body). The simulation of the incoming flow turbulence may then be of secondary importance. Nevertheless, there are many instances-where the incoming flow turbulence can play a significant role.

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