Adrian Dobre

DISPERSION EXPERIMENTS IN CENTRAL LONDON The 2007 Dapple Project

In the event of a release of toxic gas in the center of London, emergency services personnel would need to determine quickly the extent of the area contaminated. The transport of pollutants by turbulent flow within the complex streets and building architecture of London, United Kingdom, is not straightforward, and we might wonder whether it is at all possible to make a scientifically reasoned decision. Here, we describe recent progress from a major U.K. project, Dispersion of Air Pollution and its Penetration into the Local Environment (DAPPLE; information online at www.dapple.org.uk). In DAPPLE, we focus on the movement of airborne pollutants in cities by developing a greater understanding of atmospheric flow and dispersion within urban street networks. In particular, we carried out full-scale dispersion experiments in central London from 2003 through 2008 to address the extent of the dispersion of tracers following their release at street level. These measurements complemented previous studies because 1...

Wake Control Based on Spanwise Sinusoidal Perturbations

The effectiveness of a passive sinusoidal perturbation method, applied on the upstream faces of square cylinders at a wavelength that corresponds to the wavelength of the intermediate wake instability mode, is experimentally investigated. Hot-wire measurements are taken to examine the effect of three different sinusoidal perturbation amplitudes as compared to the straight cylinder case. Good agreement is found between high- and low-Reynolds-number results, suggesting that the main flow dynamics features, as well as the flow control method efficiency, are Reynolds independent. Two sets of measurements are taken: in the near and in the intermediate to far wake. The near-wake measurements show that the method is very effective in mitigating the von Karman vortices as previously found, whereas the intermediate to far wake measurements indicate that the wake decay is accelerated by the sinusoidal perturbations, therefore, being beneficial in the reduction of wake aeroelastic instabilities.

WAVELET-BASED INVESTIGATION OF THE HIGH REYNOLDS NUMBER BLUFF BODY WAKE TOPOLOGY

The high Reynolds number wake topology of a square prism is experimentally investigated using wavelet analysis. It is shown that a systematic application of one-dimensional continuous wavelet techniques, including a relatively new wavelet pattern recognition technique can reveal important three-dimensional features of the flow, assessing the validity of previously proposed wake topological models. Present results suggest that the high Reynolds number turbulent wakes are topologically similar, but not identical, to their laminar counterparts.