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Abstract.A comparison between numerical simulations and wind tunnel modelling has been performed to examine the variation with streamwise aspect ratio (width/height, W/H) of the mean flow patterns in a street canyon. For this purpose a two-dimensional (2-D) cavity was subjected to a thick turbulent boundary layer flow perpendicular to its principal axis. Five different test cases, W/H = 0.3, 0.5, 0.7, 1.0 and 2.0, have been studied experimentally with flow measurements taken using pulsedwire anemometry. The results show that the skimming flow regime, with a large vortex in the canyon, occurred for all the cases investigated. For the cavities with W/H≤0.7 a weaker secondary circulation developed beneath the main vortex. The narrower the canyon, the smaller the wind speed close to the cavity ground, giving increasingly poor ventilation qualities. The corresponding numerical results were obtained with the Computational Fluid Dynamics (CFD) code CHENSI that uses the standard k-ε model. The intercomparison showed good agreement in terms of the gross features of the mean flow for all the geometries examined, although some detailed differences were observed.

This paper describes an imeractive Eulerian-Lagrangian model of the turbulent transport of evaporating droplets. A k-e (where k is turbulem kinetic energy and • is its rate of dissipation) turbulence closure model is used to accurately simulate stable, near-neutral, and unstable boundary layers within the large air-sea interaction tunnel at the Institut de M6canique Statistique de la Turbulence (IMST), Luminy, France. These results are then used with the Lagrangian model described in part 1 [Edson and Fairall, 1994]. The coupled model is shown to give excelleto agreemere with droplet dispersion measuremeres made during the 1988 Couche Limite Unidimensionelle Stationnaire d'Embrums (CLUSE, a French acronym that translates to one-dimensional stationary droplet boundary layer) campaign. Additionally, this paper describes how the coupled model can now be used to investigate the imeraction between the evaporating droplets and the turbulent fields of temperature and humidity. The investigation shows that although the influence of the droplets is small under the conditions simulated at IMST, the potential for substamial modification of the surface energy budget exists for high-wind conditions over the ocean. addresses some of the advantages of this combined (Eulerian plus Lagrangian) approach over separate approaches (Eulerian or Lagrangian) in simulations of the turbulent transport of heavy particles. It then concludes with the results from the interactive model for simulations of droplet dispersion in both a laboratory and marine atmospheric surface layer. Copyright 1996 by the American Geophysical Union. 2. Eulerian k-½ Model Paper number 95JC03280. 0148-0227/96/95JC-03280 $5.00 The Eulerian code used in this simulation is derived from a k-e model developed at the Laboratoire de M6canique des Fluids, 1279 1280 EDSON ET AL.: EULERIAN-LAGRANGIAN MODEL OF EVAPORATING SPRAY Ecole Centrale de Nantes, France, to simulate flows around urban structures [Ldvi Alvards et al., 1990; Ldvi Alvards and Sini, 1992; Lakehal et al., 1996]. In the atmospheric surface layer, expressions for the instantaneous velocity field for incompressible fluid flow can be written OU. ' -o (1) % act, act,__ • aa o•-o• r a• * c5 % p• a•, -•" *" ' (•) where Einstein's summation notation is used and the Boussinesq approximation has been applied, v is the kinematic viscosity; ©v is the ambient virtual potential temperature; gi = (0,0,-g) where g is the gravitational acceleration; and Pa and or• and virtual potential temperature of the reference state of the fluid, respectively [LandaM and Mollo-Christensen, 1986]. In (2) the pressure field P represents the departure from the reference pressure field in hydrostatic balance. In developing equations designed to study flows where the mean departure from hydrostatic equilibrium can be nonzero (e.g., around a building), Sini [1986] and Sini and Dekeyser [1987] decomposed this departure from hydrostatic equilibrium into mean and fluctuating parts. The Reynolds averaged equations for the mean variables are then...

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In order to investigate the microclimatic conditions in a street canyon, a physical model was used to conduct the Joint ATREUS-PICADA Experiment (JAPEX) in situ experimental campaign. Four lines of buildings simulated by steel containers were installed to form three parallel street canyons at 1:5 scale, with width/height aspect ratio approximately 0.40. The reference wind and atmospheric conditions were measured, as well as the flow velocity and direction in the street. Preliminary results concern street canyon ventilation and thermal effects on in-canyon airflow, and show that vortical motions appear for reference wind directions perpendicular to the street axis. The presence of adjacent rows of buildings did not appear to significantly influence the flow character within the canyon for the case of a low aspect ratio corresponding to a skimming flow regime. The flow structure was not significantly affected by the thermal effects although some slight interference occurred in the lower part of the canyon. An analysis of horizontal temperature gradients indicated that a thin boundary layer develops near the heated facade. These facts imply that the thermal effects are considerable only very close to the wall.

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