Turbulence variances in the convective urban roughness sublayer: an application of similarity theory using local scales

Abstract

Similarity theory using local scales was applied to the normalized standard deviation of the vertical wind component, w, and potential temperature, θ , σ w /u * loc and σ θ /θ * loc , where u * loc and θ * loc are the friction velocity and temperature and 'loc' refers to variables that are locally measured. These data were obtained in a tropical city under convective atmospheric conditions within the roughness sublayer. The following parameters were assessed based on the upwind characteristics of the site, denoted as 'sectors': the non-dimensional height, z/ h (1.16 and 1.20), and the non-dimensional vertical heterogeneity, σ h /h (0.56 and 0.32). The results obey a semi-empirical relation of the formwhere z is the effective measurement height, L loc is the local Obukhov length). The resultant extrapolated near-neutral constants depend on σ h /h: (σ w /u * loc ) neutral = 1.04 and 1.27 for σ h /h = 0.56 and 0.32, in the range −0.01 > ζ loc > −20. Spectral analysis of w reveals a separation of the spectral power at low nondimensional frequencies (f < 0.03) with increasing deviation as the atmosphere approaches neutral conditions, ζ loc > −0.6 for σ h /h = 0.32. The term σ θ /u * loc follows the form (−ζ loc )− 1/3 with constants of (σ θ /θ * loc ) neutral = −1.31 and −1.34 for the two sectors, thus being independent of both σ h /h and z/ h. These findings show that similarity theory using local scales is applicable for determining σ w and σ θ in the convective roughness sublayer but depends on the vertical heterogeneity of the upwind sectors for σ w , which only affects the near-neutral σ w /u * loc constants.

Source area definition for local climate zones studies. A systematic review

“…For example, Zou et al [142,210] have demonstrated that, closer to the top of the RSL, the classical relations that govern the ISL might be applicable. They also coincide with Yusup and Lim [211] and Yusup and Anis [212], when they say that under unstable (daytime) conditions local turbulent effects might be negligible. In those cases, filtering the measured data according to weather stability (u* filtering), which is a common practice when carrying out EC [124,130,146,148], might reduce uncertainties regarding the source area definition within the RSL.…”

Energy Balance Analysis and Turbulence Profile of a Darrieus-type Vertical Axis Wind Turbine

“…23 The raw 10 Hz time series data were processed and analysed using a custom Matlab script (version R2012a, MathWorks, United States) as used in our previous urban turbulence studies. 24,25 Spike removal, Haar transform, skewness and kurtosis tests were conducted before calculating the 60-min block-averaged flow speed, turbulence and flux parameters. Data spikes, defined as velocity measurement exceeding 3.5 standard deviation of the block-averaged mean, were removed.…”