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A Note on Spatial Averaging and Shear Stresses Within Urban Canopies
Zheng-Tong Xie1, Vladimir Fuka1
1Faculty of Engineering and the Environment, University of Southampton, Southampton, SO17 1BJ UK.
Boundary-Layer Meteorology
|July 2, 2019
Summary
Accurate urban canopy models require precise shear stress parametrization. Intrinsic spatial averaging of total stress provides a more accurate representation within the urban canopy compared to comprehensive averaging.
Area of Science:
- Atmospheric Science
- Urban Meteorology
- Computational Fluid Dynamics
Background:
- One-dimensional urban models within mesoscale numerical models necessitate accurate parametrization of shear stresses, including dispersive stress and momentum sinks.
- Accurate representation of vertical momentum fluxes is crucial for simulating urban atmospheric processes.
Purpose of the Study:
- To rigorously assess the vertical variation of spatially-averaged total shear stress within an urban canopy.
- To determine the most suitable spatial averaging method for one-dimensional urban canopy models.
Main Methods:
- Utilized a case study with a 33% urban packing density.
- Analyzed and compared two spatial averaging methods: intrinsic and comprehensive.
- Investigated the vertical profile of spatially-averaged total shear stress.
Main Results:
- The intrinsic spatial average yielded a greater time-spatial average of total stress within the canopy.
- The intrinsic spatial average demonstrated a more evident abrupt change in stress at the top of the buildings.
- Comprehensive spatial averaging, which includes solid parts, resulted in different stress profiles.
Conclusions:
- Intrinsic spatial averaging is more appropriate for representing shear stress in one-dimensional urban canopy models.
- The choice of spatial averaging significantly impacts the simulation of momentum fluxes within urban canopies.
- Findings improve the accuracy of urban canopy parameterizations in mesoscale models.
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