摘要
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 smallscale 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.
The multifractality of energy and thermal dis- sipation of fully developed intermittent turbulence is in- vestigated in the urban canopy layer under unstable con- ditions by the singularity spectrum for the fractal dimen- sions of sets of singularities characterizing multifractals. In order to obtain high-order moment properties of small- scale turbulent dissipation in the inertial range, an ultra- sonic 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 sig- nificantly smaller than the singular exponents for a wind tunnel at a moderate Reynolds number. The evidence in- dicates a higher intermittency of turbulence in the urban canopy layer at a high Reynolds number, which is dem- onstrated by the data with high temporal resolution. Fur- thermore, 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.
基金
supported by the National Natural Science Foundation of China(Grant Nos.11472272 and 91215302)
the Special Fund for Meteorological Research in the Public Interest(Grant No.GYHY201206041)
关键词
多重分形
分形特征
间歇性
冠层
城市
奇异指数
高时间分辨率
湍流耗散
urban canopy layer, intermittent turbulence,turbulent dissipation, multifractality, singularity spectrum
