How vegetation in flows modifies the turbulent mixing and spreading of jets

Abstract

While studies on vegetated channel flows have been developed in many research centers, studies on jets interacting with vegetation are still rare. This study presents and analyzes turbulent jets issued into an obstructed cross-flow, with emergent vegetation simulated with a regular array of cylinders. The paper presents estimates of the turbulence diffusion coefficients and the main turbulence variables of jets issued into a vegetated channel flow. The experimental results are compared with jets issued into unobstructed cross-flow. In the presence of the cylinder array, the turbulence length-scales in the streamwise and transverse directions were reduced, relative to the unobstructed crossflow. This contributed to a reduction in streamwise turbulent diffusion, relative to the unobstructed conditions. In contrast, the transverse turbulent diffusion was enhanced, despite the reduction in length-scale, due to enhanced turbulent intensity and the transverse deflection of flow around individual cylinders. Importantly, in the obstructed condition, the streamwise and transverse turbulent diffusion coefficients are of the same order of magnitude.

Wave Height Attenuation and Flow Resistance Due to Emergent or Near-Emergent Vegetation

“…In particular, vegetation attenuates the action of waves, slows down the flow, and promotes diffusion and deposition processes [6][7][8][9][10]. Accordingly, it (i) enhances particle removal and water quality [11][12][13]; (ii) positively affects the hydrochory and nautochory of seeds and organic matter [14][15][16][17]; (iii) reduces sediment erosion and resuspension, while enhancing sediment deposition [18][19][20]; and (iv) creates preferred paths for tracers' dissipation processes [21][22][23]. This is one of the main reasons for investigations of the interaction between vegetation and flow.…”

To Investigate the Flow Structure of Discontinuous Vegetation Patches of Two Vertically Different Layers in an Open Channel

“…A large eddy simulation (LES) model was implemented by Lu et al [19] in order to analyze turbulence features like Reynolds stresses inside the vegetation concentration and to investigate the influence of immersed vegetation on solute conveyance in an open canal. Mossa and De Serio [20] and Mossa et al [21] analyzed the turbulent jets in an obstructed flow with emergent vegetation and Mossa et al [21] proved the enhancement of turbulent intensity and the transverse deflection of flow around the individual cylinders. The flow structure in a channel partially obstructed by rigid emergent vegetation was also investigated by Ben Meftah and Mossa [22].…”

Turbulence Measurement of Vertical Dense Jets in Crossflow

“…Since all components of aquatic ecosystems are very sensitive to any water quality changes, a rapid and maximum dilution of the jet discharge within the ambient flow is a key solution to keep the ecosystem healthy and sustainable. Mixing of turbulent jets within surrounding environment was the topic of numerous experimental, analytical and numerical studies [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18].…”