Jose M Redondo

Abstract: The nature and role of the shear layer, which occurs at the level of the average building height in urban canopies, are poorly understood. Velocity data are analyzed to determine the characteristics of the shear layer of the urban canopy, defined as the broad, linear segment of the mean velocity profile in a region of high shear. Particle image velocimetry measurements in a water tunnel were undertaken to resolve velocity profiles for urban canopies of two geometries typical of Los Angeles, California, and New York City, New York, for which the aspect ratios (average building height-to-width ratio) H/wb are 1 and 3, respectively. The shear layers evolve with distance differently: For H/wb 1 the urban canopy shear layer extends quickly from above the building height to ground level, whereas for H/wb 3 the urban canopy shear layer remains elevated at the vicinity of the building height, only reaching to a depth of z/H 0.5 far downstream. Profiles of the mean velocity gradient also differ from each other for urban canopies associated with H/wb of 1 or 3. Values of shear dU/dz increase toward ground level for an urban canopy associated with H/wb 1. For an urban canopy associated with H/wb 3, localized peaks of shear dU/dz exist at the building height and at ground level, with values of shear decreasing to zero at building midheight and far above the building height. A consequence of the different forms of the shear layers of the two urban canopies is that the ground-level dispersion coefficient is likely to be greater for urban canopies associated with H/wb 1 than for those associated with H/wb 3 because of an increased ventilation and exchange mechanism for cities such as Los Angeles relative to cities such as New York City that possess urban canyons.

Abstract: Home Publications Software Info Advanced Search View Basket Publicaciones / Libros Ref: L57 TURBULENT MIXING IN GEOPHYSICAL FLOWS This volume consists of thirteen selected papers that derive from the second ERCOFTAC conference on Mixing in Geophysical Flow held in Vilanova i la Geltru, Barcelona, Spain in March 1997. Some of the papers were presented at the conference while others were written specifically for this volume. Mixing in geophysical flows presents special challenges to fluid dynamicists and modelers, as it includes effects of stratification, the rotation of the Earth, and chemical and biological processes. Significant mixing is associated with turbulence, which in itself is a proorly understood area of fluid dynamics. In the presence of these complicating effects, the understanding of turbulence in natural flows is even more difficult. The papers presented here provide an example of the different techniques used in laboratory, numerical or field work that help to understand the nonhomogeneous and non-isotropic flows that produce Turbulent Mixing in geophysical Flows Author: P. F. Linden, J.M. Redondo Year: 2001 Editorial: CIMNE Notes: 319pp Contents: - On particle dispersion processes in 2D turbulence by A. Babiano - Convection from a local source of buoyancy with and without rotation by B.M. Bouhnov nd P. B. Rhines - Instability and mixing in stratified shear flows by C.P. Caulfield - Geophysical turbulence: A theory and laboratory experiments by Y.D. Chashech Lin - Small-scale processes in geophysical flows by H.J. S. Fernando and D. C. Smith - Mixing efficiency of different kinds of turbulent processes and instabilities by J.M. Redondo - Some observations of waves and turbulence in the atmospheric biundary layer by J. M. Rees - Mixing by breaking internal gravity waves by C. Staquet, P. Bouruet-Aubertot and C. Koudella - Current status of studies on mixing processes in the atmospheric by J. Vila-Guerau de Arellano, S. Galmarini and J. Chart - Jets and vortex structure formation and interactions in stratified and rotating fluids by S.I. Voropayeu - Geophysical examples of turbulent buoyant plumes by A. W. Woods - On peculiarties and similarities of the coherent structure formation in stratified and rotating fluid by A. G. Zatsepin - Large-scale quasigeostrophic vortices and their transport properties by V. Zeitlin - Author index ISBN: 84-89925-98-4

Abstract: The oil pollution of Gulf of Lion in the NW Mediterranean has been studied with SAR images during the period 1999 -2005. We have analyzed these SAR images with respect to other surface features such as wind, river plumes, eddies and convergence areas. Some results of our statistical analysis are presented showing that the NW Mediterranean is most polluted along the main ship traffic routes, but comparatively less that near other routes in the Indic and the Pacific. The oils spill index is higher than one. The sizes of the detected oil spills vary over a large range, and if the statistics of the largest accidents are also considered on a longer timescale, we show that Zipf's Law, relating the frequency and the size of the spill in a hyperbolic fashion is applicable. Advanced image analysis techniques, such as the calculation of the multi-fractal dimensions of the observed SAR signatures, have been applied to distinguish between natural slicks and antropogenic spills. Fractal dimensions can also be used to predict the time of release of the spill, non-dimensionalised with local turbulent dissipation. The multi-scale appearance and the topological structure of the slicks and spills may also be used as a useful measure of the diffusivity, yielding additional information which in turn may improve automated detection algorithms and be used in numerical models.