TY - JOUR

T1 - Dispersive Fluxes Within and Over a Real Urban Canopy

T2 - A Large-Eddy Simulation Study

AU - Akinlabi, Emmanuel

AU - Maronga, Björn

AU - Giometto, Marco G.

AU - Li, Dan

N1 - Funding Information: This research was funded by National Science Foundation (NSF) under the Award number AGS-1853354 and ICER-1854706 and Army Research Office (ARO) under the Award Number W911NF-18-1-0360. We acknowledge the high-performance computing support from Cheyenne ( https://doi.org/10.5065/D6RX99HX ) provided by NCAR's Computational and Information Systems Laboratory, sponsored by the National Science Foundation. Finally, we thank the PALM group at the Institute of Meteorology and Climatology of Leibniz Universität Hannover, Germany for their technical support.

PY - 2022/10

Y1 - 2022/10

N2 - Large-eddy simulations (LES) are conducted to study the transport of momentum and passive scalar within and over a real urban canopy in the City of Boston, USA. This urban canopy is characterized by complex building layouts, densities and orientations with high-rise buildings. Special attention is given to the magnitude, variability and structure of dispersive momentum and scalar fluxes and their relative importance to turbulent momentum and scalar fluxes. We first evaluate the LES model by comparing the simulated flow statistics over an urban-like canopy to data reported in previous studies. In simulations over the considered real urban canopy, we observe that the dispersive momentum and scalar fluxes can be important beyond 2–5 times the mean building height, which is a commonly used definition for the urban roughness sublayer height. Above the mean building height where the dispersive fluxes become weakly dependent on the grid spacing, the dispersive momentum flux contributes about 10–15% to the sum of turbulent and dispersive momentum fluxes and does not decrease monotonically with increasing height. The dispersive momentum and scalar fluxes are sensitive to the time and spatial averaging. We further find that the constituents of dispersive fluxes are spatially heterogeneous and enhanced by the presence of high-rise buildings. This work suggests the need to parameterize both turbulent and dispersive fluxes over real urban canopies in mesoscale and large-scale models.

AB - Large-eddy simulations (LES) are conducted to study the transport of momentum and passive scalar within and over a real urban canopy in the City of Boston, USA. This urban canopy is characterized by complex building layouts, densities and orientations with high-rise buildings. Special attention is given to the magnitude, variability and structure of dispersive momentum and scalar fluxes and their relative importance to turbulent momentum and scalar fluxes. We first evaluate the LES model by comparing the simulated flow statistics over an urban-like canopy to data reported in previous studies. In simulations over the considered real urban canopy, we observe that the dispersive momentum and scalar fluxes can be important beyond 2–5 times the mean building height, which is a commonly used definition for the urban roughness sublayer height. Above the mean building height where the dispersive fluxes become weakly dependent on the grid spacing, the dispersive momentum flux contributes about 10–15% to the sum of turbulent and dispersive momentum fluxes and does not decrease monotonically with increasing height. The dispersive momentum and scalar fluxes are sensitive to the time and spatial averaging. We further find that the constituents of dispersive fluxes are spatially heterogeneous and enhanced by the presence of high-rise buildings. This work suggests the need to parameterize both turbulent and dispersive fluxes over real urban canopies in mesoscale and large-scale models.

KW - Dispersive fluxes

KW - Large-eddy simulation

KW - Real urban canopy

KW - Urban roughness sublayer

UR - http://www.scopus.com/inward/record.url?scp=85135321026&partnerID=8YFLogxK

U2 - 10.1007/s10546-022-00725-6

DO - 10.1007/s10546-022-00725-6

M3 - Article

AN - SCOPUS:85135321026

VL - 185

SP - 93

EP - 128

JO - Boundary-Layer Meteorology

JF - Boundary-Layer Meteorology

SN - 0006-8314

IS - 1

ER -