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A neutral boundary layer was generated in the laboratory to analyze the meanvelocity field and the turbulence field within and above an array oftwo-dimensional obstacles simulating an urban canopy. Different geometricalconfigurations were considered in order to investigate the main characteristicsof the flow as a function of the aspect ratio (AR) of the canopy. To this end,a summary of the two-dimensional fields of the fundamental turbulenceparameters is given for AR ranging from 1 to 2. The results show that the flowfield depends strongly on AR only within the canyon, while the outer flow seemsto be less sensitive to this parameter. This is not true for the verticalmomentum flux, which is one of the parameters most affected by AR, both withinand outside the canyon. The experiments also indicate that, when (i.e. theskimming flow regime), the roughness sub-layer extends up to a height equal to1.25 times the height of the obstacles (H), surmounted by an inertial sub-layerthat extends up to 2.7 H. In contrast, for (i.e. the wake-interference regime)the inertial sub-layer is not present. This has significant implications whenusing similarity laws for deriving wind and turbulence profiles in canopyflows. Furthermore, two estimations of the viscous dissipation rate ofturbulent kinetic energy of the flow are given. The first one is based on thefluctuating strain rate tensor, while the second is related to the mean strainrate tensor. It is shown that the two expressions give similar results, but theformer is more complicated, suggesting that the latter might be used innumerical models with a certain degree of reliability. Finally, the datapresented can also be used as a dataset for the validation of numerical models.

Water-channel study of flow and turbulence past a two-dimensional array of obstacles