Wavelet Analysis Of Spectral Energy Transfers In Urban Turbulence

Orthogonal wavelets are applied to turbulent flow over a cubical building array. The transfer spectrum, which depends on scale and spatial location, characterises nonlinear energy transfers from one scale to another. Using large-eddy simulation, the interscale energy transfer is decomposed into discrete modes and comparisons made with the usual Fourier spectrum. Spatial variability is quantified with the standard deviations or dual spectra. Wavelet decomposition of the spectral energy transfer shows that energy is cascaded from large to small scales in both the inertial sublayer and outer layer. There is also indication of energy backscatter in the roughness sublayer as shown by the scale-filtered reconstruction error. Based on the urban turbulent flow at various heights, the choice of wavelet basis is also discussed. This work is relevant to the development of multiscale urban canopy characterizations that seek to model the energy transfers between regional and urban scales.