Turbulent Intensities and Velocity Spectra for Bare and Forested Gentle Hills: Flume Experiments

摘要: To investigate how velocity variances and spectra are modified by the simultaneous action of topography canopy, two flume experiments were carried out on a train gentle cosine hills differing in surface cover. The first experiment was conducted above bare while second within densely arrayed rod canopy. from these compared middle, inner, near-surface layers. In middle layer, for canopy surface, longitudinal vertical (\({\sigma_u^2,\sigma_w^2}\)) phase with hill-induced spatial mean perturbation (Δu) around so-called background state (taken here as at given height) predicted rapid distortion theory (RDT). However, case, \({\sigma_u^2 }\) \({\sigma_w^2 remained Δu about L/2, where L is hill half-length. wake production significant source turbulent energy , its to re-align those layers, mechanism completely absent case. Such lower ‘boundary condition’ resulted variations \({\sigma_w^2}\) be nearly surface. inner spectral distortions case but not particular, layers effective exponents derived locally measured power diverged their expected − 5/3 value inertial subrange scales. These departures spatially correlated near though minor differences also Inside short-circuiting 5/3. appeared through contribution alignment Δu. Moreover, scales commensurate Von Karman street vorticies well described inside confirming important role flow producing wakes. lee side hill, negative delineated recirculation zone, suggested that there ‘broader’ when counterpart outside zone. significantly more higher frequencies regions