Evidence for Raupach <i>et al.</i>'s mixing-layer analogy in deep homogeneous urban-canopy flows

The mixing-layer analogy is due to Raupach, Finnigan &amp; Brunet ( Boundary-Layer Meteorol. , vol. 25, 1996, pp. 351–382). In the analogy, flow in roughness sublayer of a homogeneous deep vegetation canopy boundary layer analogous plane mixing rather than surface layer. Evidence for includes inflected velocity profile, which resembles profile layer, and, most notably, following estimate as result Kelvin–Helmholtz instability: $\varLambda _x=8.1L_s$ where _x$ spacing large-scale eddies, and $L_s$ shear length. has been very successful research, but received only limited support urban-canopy research. This work revisits Raupach et al. 's we present evidence flows: exponential i.e. $(U-U_c)/(U_h-U_c)=\exp (z/L_m)$ $L_m\sim [(U_h/U_c-1)(U_h/U_c+3)]^{-1}$ . Here, $z$ vertical coordinate, $L_m$ attenuation length measure largest eddy $U_h$ wind speed at crest $U_c$ inactive We conduct direct numerical simulations various flows test above two scalings. also discuss why not seen many successes flows.