Flow near a building model in a family of surface layers

Abstract

A family of thick turbulent boundary layers with different characteristics was generated by the counter-jet technique and used to simulate neutral atmospheric surface layers. These selected “test boundary layers” were utilized to examine the response of the flowfield near a building model to variations in the characteristics of these turbulent layers. The counter-jets, applied at the wall near the entrance of a moderate length test section, permit rapid alteration of reproducible boundary layers from outside the tunnel while experiments are in progress. The mean and unsteady characteristics of the test boundary layers were documented through profiles of mean velocity, turbulence intensity, integral scales, and Reynolds stress, and through velocity spectra. The substantial deviations of the atmospheric surface layer, in time and space, from over-idealized standard layers led us to the “sensitivity testing” approach. For example, using simulated surface layers which bracket the variations in the atmospheric conditions, this approach provides valuable information through the bracketing of wind loads or pressure distributions by extreme values. This sensitivity study employs four substantially different test boundary layers, and involves a building model at two orientations to the wind. Changes in salient features of the flow over and around the bluff body and in its wake were revealed through profiles of mean velocity and turbulence intensity. In particular, the development of the shear layers above and downstream of the building displayed a strong dependence on the test boundary layer used.