# Large-Eddy-Simulation Study of the Effects of Building-Height Variability on Turbulent Flows over an Actual Urban Area

Large-Eddy-Simulation Study of the Effects of Building-Height Variability on Turbulent Flows over... Large-eddy simulation (LES) is used to investigate the effects of building-height variability on turbulent flows over an actual urban area, the city of Kyoto, which is reproduced using a 2-m resolution digital surface dataset. Comparison of the morphological characteristics of Kyoto with those of European, North American, and other Japanese cities indicates a similarity to European cities but with more variable building heights. The performance of the LES model is validated and found to be consistent with turbulence observations obtained from a meteorological tower and from Doppler lidar. We conducted the following two numerical experiments: a control experiment using Kyoto buildings, and a sensitivity experiment in which all the building heights are set to the average height over the computational region $$h_{all}$$ h all . The difference of Reynolds stress at height $$z=2.5h_{all}$$ z = 2.5 h all between the control and sensitivity experiments is found to increase with the increase in the plan-area index ( $$\lambda _p$$ λ p ) for $$\lambda _p > 0.32$$ λ p > 0.32 . Thus, values of $$\lambda _p\approx 0.3$$ λ p ≈ 0.3 can be regarded as a threshold for distinguishing the effects of building-height variability. The quadrant analysis reveals that sweeps contribute to the increase in the Reynolds stress in the control experiment at a height $$z= 2.5h_{all}$$ z = 2.5 h all . The exuberance in the control experiment at height $$z=0.5h_{all}$$ z = 0.5 h all is found to decrease with increase in the building-height variability. Although the extreme momentum flux at height $$z=2.5h_{all}$$ z = 2.5 h all in the control experiment appears around buildings, it contributes little to the total Reynolds stress and is not associated with coherent motions. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Boundary-Layer Meteorology Springer Journals

# Large-Eddy-Simulation Study of the Effects of Building-Height Variability on Turbulent Flows over an Actual Urban Area

Boundary-Layer Meteorology, Volume 168 (1) – Mar 3, 2018
27 pages

/lp/springer_journal/large-eddy-simulation-study-of-the-effects-of-building-height-ybMjhJvosj
Publisher
Springer Journals
Subject
Earth Sciences; Atmospheric Sciences; Meteorology; Atmospheric Protection/Air Quality Control/Air Pollution
ISSN
0006-8314
eISSN
1573-1472
D.O.I.
10.1007/s10546-018-0344-8
Publisher site
See Article on Publisher Site

### Abstract

Large-eddy simulation (LES) is used to investigate the effects of building-height variability on turbulent flows over an actual urban area, the city of Kyoto, which is reproduced using a 2-m resolution digital surface dataset. Comparison of the morphological characteristics of Kyoto with those of European, North American, and other Japanese cities indicates a similarity to European cities but with more variable building heights. The performance of the LES model is validated and found to be consistent with turbulence observations obtained from a meteorological tower and from Doppler lidar. We conducted the following two numerical experiments: a control experiment using Kyoto buildings, and a sensitivity experiment in which all the building heights are set to the average height over the computational region $$h_{all}$$ h all . The difference of Reynolds stress at height $$z=2.5h_{all}$$ z = 2.5 h all between the control and sensitivity experiments is found to increase with the increase in the plan-area index ( $$\lambda _p$$ λ p ) for $$\lambda _p > 0.32$$ λ p > 0.32 . Thus, values of $$\lambda _p\approx 0.3$$ λ p ≈ 0.3 can be regarded as a threshold for distinguishing the effects of building-height variability. The quadrant analysis reveals that sweeps contribute to the increase in the Reynolds stress in the control experiment at a height $$z= 2.5h_{all}$$ z = 2.5 h all . The exuberance in the control experiment at height $$z=0.5h_{all}$$ z = 0.5 h all is found to decrease with increase in the building-height variability. Although the extreme momentum flux at height $$z=2.5h_{all}$$ z = 2.5 h all in the control experiment appears around buildings, it contributes little to the total Reynolds stress and is not associated with coherent motions.

### Journal

Boundary-Layer MeteorologySpringer Journals

Published: Mar 3, 2018

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