Effects of trees on mean wind, turbulence and momentum exchange within and above a real urban environment

Giometto, M. G.; Christen, Andreas; Egli, Pascal; Schmid, M. F.; Tooke, Rory; Coops, Nicholas C.; Parlange, Marc B.

doi:10.1016/j.advwatres.2017.06.018

Cited by 82 publications

(63 citation statements)

References 119 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The surface topography is then identified by the zero level set

\overset{Ψ}{true} false(x, y, z false) = 0

. Our implementation of the immersed boundary method is similar to the one proposed in Chester et al () and has been recently used to investigate the characteristics of urban canopy layers (Giometto et al, , ).…”

Section: Methodsmentioning

confidence: 99%

“…This version of the LES and its wall model were tested and adopted to investigate the performance of a number of SGS models (Bou-Zeid et al, 2005;Meneveau et al, 1996;Porté-Agel et al, 2000), land-atmosphere interactions (Albertson & Parlange, 1999), wind-farm effects on the atmospheric boundary layer (Sharma et al, 2016), turbulent flows over realistic urban canopy layers (Giometto et al, 2017(Giometto et al, , 2016, and drifting snow sublimation (Sharma et al, 2018).…”

Section: Lesmentioning

confidence: 99%

See 1 more Smart Citation

Preferential Deposition of Snow and Dust Over Hills: Governing Processes and Relevant Scales

et al. 2019

View full text Add to dashboard Cite

Preferential deposition of snow and dust over complex terrain is responsible for a wide range of environmental processes and accounts for a significant source of uncertainty in the surface mass balances of cold and arid regions. Despite the growing body of literature on the subject, previous studies reported contradictory results on the location and magnitude of deposition maxima and minima. This study aims at unraveling the governing processes of preferential deposition in a neutrally stable atmosphere and to reconcile seemingly inconsistent results of previous works. For this purpose, a comprehensive modeling approach is developed, based on large eddy simulations of the turbulent airflow, Lagrangian stochastic model of particle trajectories, and immersed boundary method to represent the underlying topography. The model is tested against wind tunnel measurements of dust deposition around isolated and sequential hills. A scale analysis is then performed to investigate the dependence of snowfall deposition on the particle Froude and Stokes numbers, which fully account for the governing processes of inertia, flow advection, and gravity. Model results suggest that different deposition patterns emerge from different combinations of dimensionless parameters, with deposition maxima located either on the windward or the leeward slope of the hill. Additional simulations are performed, to test whether the often used assumption of inertialess particles yields accurate deposition patterns. Results indicate that this assumption can be justified when snowflakes present dendritic shape but may generate unrealistic results for rounded particles. We finally show that our scale analysis provides qualitatively similar results for hills with different aspect ratios.

show abstract

“…The surface topography is then identified by the zero level set

\overset{Ψ}{true} false(x, y, z false) = 0

Section: Methodsmentioning

confidence: 99%

Section: Lesmentioning

confidence: 99%

Preferential Deposition of Snow and Dust Over Hills: Governing Processes and Relevant Scales

et al. 2019

View full text Add to dashboard Cite

show abstract

“…Such effects not only can improve thermal comfort at the pedestrian level, but also reduce the building energy consumption in the Summertime (Souch and Souch, 1993;Akbari et al, 2001). On the other hand, the urban trees are thought to be a sink of momentum and kinetic energy by exerting drag and damping the flow fluctuations (Giometto et al, 2017;Yuan et al, 2017). This effect cannot be modelled very well by VCWG, which predicts the same level of wind speed within the canyon at all LADs.…”

Section: Leaf Area Densitymentioning

confidence: 98%

The Vertical City Weather Generator (VCWG v1.0.0)

Moradi¹,

Dyer²,

Nazem³

et al. 2019

Preprint

View full text Add to dashboard Cite

Abstract. The Vertical City Weather Generator (VCWG) is a computationally efficient urban microclimate model developed to predict temporal and vertical variation of temperature, wind speed, and specific humidity. It is composed of various sub models: a rural model, an urban microclimate model, and a building energy model. In a nearby rural site, a rural model is forced with weather data to solve a vertical diffusion equation to calculate vertical potential temperature profiles using a novel parameterization. The rural model also calculates a horizontal pressure gradient. The rural model outputs are then forced on a vertical diffusion urban microclimate model that solves vertical transport equations for momentum, temperature, and specific humidity. The urban microclimate model is also coupled to a building energy model using feedback interaction. The aerodynamic and thermal effects of urban elements and vegetation are considered in VCWG. To evaluate the VCWG model, a microclimate field campaign was held in Guelph, Canada, from 15 July 2018 to 5 September 2018. The meteorological measurements were carried out under a comprehensive set of wind directions, wind speeds, and thermal stability conditions in both the rural and the nearby urban areas. The model evaluation indicated that the VCWG predicted vertical profiles of meteorological variables in reasonable agreement with field measurements for selected days. In comparison to measurements, the overall model biases for potential temperature, wind speed, and specific humidity were within 5 %, 11 %, and 7 %, respectively. The performance of the model was further explored to investigate the effects of urban configurations such as plan and frontal area densities, varying levels of vegetation, seasonal variations, different climate zones, and time series analysis on the model predictions. The results obtained from the explorations were reasonably consistent with previous studies in the literature, justifying the reliability and computational efficiency of VCWG for operational urban development projects.

show abstract

“…Vegetation decelerates the flow due to the form and viscous drag forces, and the decelerating force depends on the wind velocity and plant area density (PAD, m 2 m −3 ). Despite the model has previously been developed for continuous vegetation, it has also been used for individual trees (e.g., [19,41]). For this study, the canopy model was revised to allow a heterogeneous distribution of tree canopy.…”

Section: Model Descriptionmentioning

confidence: 99%

“…Thus, the PAD profiles of the trees outside the boulevard are constructed based on their height relative to the street trees. In all simulations, a drag coefficient C D = 0.2 is assigned following previous LES studies considering ABL flows individual trees (e.g., [41]) and forest canopies (e.g., [38,49]). …”

Section: Tree Canopy Modelmentioning

confidence: 99%

Ventilation and Air Quality in City Blocks Using Large-Eddy Simulation—Urban Planning Perspective

et al. 2018

View full text Add to dashboard Cite

Buildings and vegetation alter the wind and pollutant transport in urban environments. This comparative study investigates the role of orientation and shape of perimeter blocks on the dispersion and ventilation of traffic-related air pollutants, and the street-level concentrations along a planned city boulevard. A large-eddy simulation (LES) model PALM is employed over a highly detailed representation of the urban domain including street trees and forested areas. Air pollutants are represented by massless and passive particles (non-reactive gases), which are released with traffic-related emission rates. High-resolution simulations for four different city-block-structures are conducted over a 8.2 km 2 domain under two contrasting inflow conditions with neutral and stable atmospheric stratification corresponding the general and wintry meteorological conditions. Variation in building height together with multiple cross streets along the boulevard improves ventilation, resulting in 7-9% lower mean concentrations at pedestrian level. The impact of smaller scale variability in building shape was negligible. Street trees further complicate the flow and dispersion. Notwithstanding the surface roughness, atmospheric stability controls the concentration levels with higher values under stably stratified inflow. Little traffic emissions are transported to courtyards. The results provide urban planners direct information to reduce air pollution by proper structural layout of perimeter blocks.

show abstract

Effects of trees on mean wind, turbulence and momentum exchange within and above a real urban environment

Cited by 82 publications

References 119 publications

Preferential Deposition of Snow and Dust Over Hills: Governing Processes and Relevant Scales

Preferential Deposition of Snow and Dust Over Hills: Governing Processes and Relevant Scales

The Vertical City Weather Generator (VCWG v1.0.0)

Ventilation and Air Quality in City Blocks Using Large-Eddy Simulation—Urban Planning Perspective

Contact Info

Product

Resources

About