SEMINAR
DEPARTMENT OF MECHANICAL ENGINEERING

Quantifying the impact of trees on turbulent transport in the urban boundary layer: insight from large-eddy simulation and theoretical models 

Prof. Marco Giometto 

Dept. of Civil Engineering and Engineering Mechanics , Columbia University

Abstract

Accurate modeling of turbulent transport over and within urban canopies is crucial to properly predict local weather and pollutant dispersion in cities. Trees are an integral part of the urban landscape, and in many suburban neighborhoods tree cover reaches up to 30% of the available surface. Current understanding of the impact of urban trees on mean wind and turbulence in cities is poor, and it hence comes as no surprise that urban trees are not properly accounted for in urban climate and weather forecasting models. With the aim of bridging this knowledge gap, in this work we leverage Large-Eddy Simulation (LES) to gain insight on the impact of trees on momentum and energy transport in the atmosphere over and within a realistic urban canopy. The urban canopy is representative of the Sunset neighborhood in the city of Vancouver, BC, Canada, where a small fraction of trees are taller than buildings. Our work shows that trees can have a strong, seasonal impact on the aerodynamic parameters characterizing the urban surface. For example, the aerodynamic drag coefficient characterizing the considered canopy during winter, when deciduous trees have no leaves, is about a third of that during the summer season. Further, urban trees not only act as a direct momentum sink for the flow, but also reduce downward turbulent transport of high-momentum fluid, thus significantly reducing the wind intensity at the heights where people live in the city. A physics-based reduced-order model for the drag partition problem is also presented, which is able to correctly capture the aerodynamic interaction between buildings and trees. The model will be used to further discuss flow dynamics of the urban atmosphere.

Biography

Dr. Giometto is an Assistant Professor in the Civil Engineering and Engineering Mechanics department at Columbia University. He received his BS and MS degrees in civil engineering from the University of Padua (2010), and a joint PhD in civil and environmental engineering from Braunschweig TU University and the University of Florence (2014). In 2016 he earned a second PhD in mechanical engineering from École Polytechnique Fédérale de Lausanne, where he won the EDME Award for the best thesis in mechanical engineering. Before joining Columbia University in 2018, he held postdoctoral positions at the University of British Columbia and at the Center for Turbulence Research, which is jointly operated by Stanford University and NASA Ames.