Experimental investigation of 3D flow properties around emergent rigid vegetation

Abstract

The condition of emergent or submerged vegetation plays a vital role in affecting the flow behaviour in open channels. To understand the flow processes in free surface flows under emergent rigid vegetation condition, an extensive experimental investigation is performed in a laboratory channel with staggered combination of emergent rigid vegetation. Three-dimensional velocities data are collected by ADV at various section and position of vegetated channel. The three-dimensional flow properties such as velocity distribution, turbulence intensity, turbulent kinetic energy, Reynolds shear stress in vegetation, and non-disturbed region are analysed and compared with the longitudinal and transverse length of vegetated zone. In the vegetation region, the longitudinal velocity in free stream region decreases as compared with nondisturbed region. However, the vertical velocity also decreases in free stream region except at the centre line of channel cross-section. Variations in velocity in the vegetation section were observed because of the local effect induced by the vegetation stems. Three-dimensional Reynolds shear stress and turbulent intensity were weaker in magnitude at vegetation region. The presence of vegetation reduces the longitudinal profile of flow velocity, Reynolds shear stress and turbulence intensities, which means that vegetation can be used as an effective tool to reduce the flow resistance.The turbulent kinetic energy, skewness and kurtosis are also evaluated and compared between the vegetated and non-vegetated zone. The outcomes of the results provide an important view to understand flow behaviour at immediately front and immediately behind of vegetation stem.

Turbulence Kinetic Energy and High-Order Moments of Velocity Fluctuations of Flows in the Presence of Submerged Vegetation in Pools

“…Furthermore, the presence of vortexes leads to an increase in the TKE [3,[14][15][16]. In 2D flows in channels with emergent vegetation elements, instabilities caused by horizontal vortexes at the downstream edge of a vegetation patch play a dominant role in flow structures [17,18]. In the presence of a vegetation canopy layer in a flow, an analogy between the canopy layer and the flow's mixing layer has been reported [19,20].…”

Investigation of the Influence of Reed Vegetation on the Hydraulic Characteristics of the Huai River Inflow Channel

“…Baruah et al [15] proposed a new entropy-based vertical velocity distribution model by linking the two-dimensional shallow water model (SWM) with Shanon's entropy theory, based on the randomness in velocity profiles under different inundation levels and vegetation densities, expressed explicitly by channel entropy parameters. Pritam et al [16] analyzed the three-dimensional flow characteristics such as velocity distribution, turbulence intensity, turbulent kinetic energy, and Reynolds shear stress in vegetation and undisturbed areas and compared them with the longitudinal and transverse lengths of vegetation areas. The presence of vegetation reduces the flow velocity profile, Reynolds shear stress, and turbulence intensity, which means that vegetation can be an effective tool for reducing flow resistance.…”

Flow resistance of emergent rigid vegetation in steady flow

“…Many experiments have been conducted in the field and in laboratory flumes using different shapes of natural or artificial materials to model aquatic vegetation arranged in different arrays (uniform, staggered, or random) under various flow and sediment conditions (uniform or non-uniform flow, with or without sediment transport), studying the effect of vegetation on flow resistance and hydraulic characteristics (Wang et al, 2014;Zhang et al, 2020). Based on the measurements of hydraulic parameters like upstream and downstream water levels and flow velocities, insight has been provided into the three-dimensional velocity distribution and turbulent flow structure (Kumar and Sharma, 2022;Li et al, 2014;Nezu and Sanjou, 2008). Noting the importance of estimating the hydraulic resistance, only a few studies have directly measured the drag force acting on vegetation (Armanini et al, 2005;Tinoco and Cowen, 2013;Zhao et al, 2014b), with most researchers using velocity and pressure data to infer the flow resistance.…”