Dynamics of the flow inside an urban canopy : Study of the flow in the vicinity of a cube immersed in a thick turbulent boundary layer
Résumé
The flow inside an idealized urban canopy consisting of an staggered array of cubes with a 25% density,
immersed into an atmospheric surface layer with a Reynolds number of Re δ = δ + = 32300 is investi-
gated by means of Laser Doppler Anemometry. The cube boundary layer thickness to cube height ratio
δ/h = 22.7 as well as the Reynods number based on the cube height h + = 1420 are large enough to be
representative of engineering applications. The LDA data gives access to pointwise time-resolved data
at several positions inside the canopy (z = h/4, h/2, and h) and is compared with LES data of a similar
canopy, at h + = 500 with parameters close the DNS data from [5]. The wall-normal mean velocity
profile and Reynolds stresses of both the LDA and LES data show a good agreement with available
data in the literature, although some differences are observed on the standard deviation of the spanwise
component. Maps of the flow in wall-normal planes inside the canopy extracted from the LES data are analyzed and allow a better understanding of organization of the canopy flow. Values at the positions
of the LDA measurements points are extracted from the LES data and show a reasonnable agreement.
A detailed spectral analysis is then carried out using the LDA data. To our knwowledge, this is the first
time such results are shown on the evolution of the power spectral density inside the canopy.