A mixing-length model for predicting vertical velocity distribution in flows through emergent vegetation

Abstract

The vertical profiles of streamwise velocities are computed on flood plains vegetated with trees. The calculations were made based on a newly developed onedimensional model, taking into account the relevant forces acting on the volumetric element surrounding the considered vegetation elements. A modified mixing length concept was used in the model. An important by-product of the model is the method for evaluating the friction velocities, and consequently bed shear stresses, in a vegetated channel. The model results were compared with the relevant experimental results obtained in a laboratory flume in which flood plains were covered by simulated vegetation.

The mechanism of energy loss and transition in a flow with submerged vegetation

“…The energy borrowed from local flow is always greater than the local energy spending; therefore, surplus energy borrowing will accumulate [8]. Notice that in this figure, the shear stresses τ +dτ and τ are surface forces, and both γS and f cd are body forces per unit volume [10]. dτ/dy in the control equation is also a body force per unit volume and is given by ((τ +dτ) -τ) × dx × 1/(dxdz ×1).…”

“…Some researchers have regarded aquatic vegetation as parts of roughness in the riverbed and studied the vegetative resistance acting on the flow [4,6,9], but they usually did not describe how the vegetation influenced the flow in detail. In recent years, more researchers have been interested in the vertical distributions of the stream-wise velocity [7,10] and Reynolds stress [2,5,14]. Ghisalberti and Nepf [3] further studied the coherent structure of flow resulting from submerged vegetation and pointed out [8] that the vertical exchanges of mass, momentum and energy were dominated by two scales of vortices: the shear-scale vortices generated and stem-scale vortices (Fig.…”

Study on roughness coefficient for unsubmerged reed in the Changjiang Estuary

“…As presented by Rowinski and Kubrak (2002), it can be assumed that the drag force of vegetation per unit water volume may be described as…”

Multilayer Numerical Modeling of Flows through Vegetation Using a Mixing-Length Turbulence Model

“…To be solved and for computational convenience, this system is reduced by substituting Equations (19) and (20) in (21), in which η n+1 i,j are the only unknowns. The present numerical model has been validated and applied for different cases of study.…”

“…These models are based on 2D nonlinear diffusion, which implies that the advection processes and turbulence are completely ignored. Other models numerically solve the hydrodynamic equations, including vegetation shear stress, such as the one-dimensional model of Rowinski and Kubrak [19], the two-dimensional model (depth-integrated) of Arega and Sanders [20] and the three-dimensional models of Fischer-Antze et al [21], Choi and Kang [22] and others [23][24][25]. One of the difficulties in numerical modeling is to define a proper turbulence model.…”