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Multifractal Characteristics of Intermittent Turbulence in the Urban Canopy Layer |
XU Jing-Jing1,2, HU Fei2 |
1International Center for Climate and Environment Science (ICCES), Institute of Atmospheric Physics, Chinese Academy of Science, Beijing 100029, China
2State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China |
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Abstract The multifractality of energy and thermal dissipation of fully developed intermittent turbulence is investigated in the urban canopy layer under unstable conditions by the singularity spectrum for the fractal dimensions of sets of singularities characterizing multifractals. In order to obtain high-order moment properties of small-scale turbulent dissipation in the inertial range, an ultrasonic anemometer with a high sampling frequency of 100 Hz was used. The authors found that the turbulent signal could be singular everywhere. Moreover, the singular exponents of energy and thermal dissipation rates are most frequently encountered at around 0.2, which is significantly smaller than the singular exponents for a wind tunnel at a moderate Reynolds number. The evidence indicates a higher intermittency of turbulence in the urban canopy layer at a high Reynolds number, which is demonstrated by the data with high temporal resolution. Furthermore, the temperature field is more intermittent than the velocity field. In addition, a large amount of samples could be used for verification of the results.
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Received: 28 September 2014
Revised: 18 December 2014
Accepted: 23 December 2014
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Corresponding Author:
HU Fei
E-mail: hufei@mail.iap.ac.cn
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