The main objective of this research project is to quantify Lagrangian and Eulerian statistics from a water-channel experiment of an idealized two-dimensional urban canopy flow in neutral conditions. In particular, the fields of the Eulerian and Lagrangian time scales of the turbulence will be investigated together with their dependence on the aspect ratio of the canopy AR, i.e. the ratio of the width to the height of the canyon. The latter must be considered as an archetype for more complex geometrical situations generally found in real cities. The Lagrangian time scale (TL) is a key parameter for pollutant dispersion modelers; however, its experimental determination is still a difficult task, particularly in the case of inhomogeneous, turbulent flows. For this reason, that issue has not been much addressed in the past and there is still a lack of knowledge on TL because of measurements difficulties. Therefore, we aim to determine its spatial distribution as well as to establish its possible functional dependence on the AR.
Lagrangian velocity measurements will be performed using a feature tracking technique that recognizes particle trajectories by means of a dedicated algorithm. With this technique individual particle trajectories are illuminated throughout a volume of the flow and tracked using a camera. Though particle tracking has previously been used in the past to obtain experimentally Lagrangian statistics, measurements permitting the direct estimation of Lagrangian time scales of turbulence pertaining to canopy flows have not been reported in the literature.
In addition, Eulerian quantities such as mean velocity, velocity variance, momentum flux, dissipation rate of turbulent kinetic energy and the Eulerian time scale will be also determined for each of the AR considered in the study. Information on other parameters of the turbulence of interest in dispersion studies such as the eddy diffusivity of momentum and the Kolmogorov constant will also be given.
