资源环境科技发展态势分析平台

The scalar roughness length and laminar resistance are necessary for computing scalar fluxes in numerical simulations and experimental studies. Their dependence on flow properties such as the Reynolds number remains controversial. In particular, two important power laws (1/4 and 1/2), both having strong theoretical foundations, have been widely used in various parameterizations and models. Building on a previously proposed phenomenological model for interactions between the viscous sublayer and the turbulent flow, it is shown here that the two scaling laws can be reconciled. The 1/4 power law corresponds to the situation where the vertical diffusion is balanced by the temporal change or advection due to a constant velocity in the viscous sublayer, while the 1/2 scaling corresponds to the situation where the vertical diffusion is balanced by the advection due to a linear velocity profile in the viscous sublayer. In addition, the recently proposed 1 power law scaling is also recovered, which corresponds to the situation where molecular diffusion dominates the scalar budget in the viscous sublayer. The formulation proposed here provides a unified framework for understanding the onset of these different scaling laws and offers a new perspective on how to evaluate them experimentally.