Vegetated mixing layer around a finite‐size patch of submerged plants: Part 2. Turbulence statistics and structures

Abstract

Dynamics of vegetated mixing layer displays analogy with canonical and shallow mixing layers. Universality of turbulence and minor influence of flexible aquatic plants on the individual turbulent eddies are anticipated as the prerequisites for the analogy. This paper explores theoretically and experimentally some aspects of analogy by examining spatial patterns of turbulence characteristics around a finite‐size patch of submerged flexible vegetation the population density of which was varied between the experimental runs [Sukhodolova and Sukhodolov, 2012]. It introduces analysis of turbulent shear stress, kinetic energy, dissipation rate, and periodicity of organized motions inside the vegetated mixing layer. The theory is compared with the field experiments. The results of the study indicate that the flow structure around the patch with dense population agrees well with the proposed theoretical scaling relations and reveals many aspects of the analogy to hydrodynamic mixing layers. Around the patch with sparse vegetation the flow structure is best represented by a perturbed boundary layer model. These conclusions on the dynamics of the flow are supported by the analysis of scaled turbulence characteristics. The patterns of turbulence profiles are approximated by scaling functions fairly well while the values of scaling parameters differ from the values reported for canonical and shallow mixing layers. This is an important result which agrees with the previous reports of laboratory research with model vegetation and is explained by a combined effect of internal shear and friction at the top of the canopy.