Flow and scalar transfer characteristics for a circular colony of vegetation

Abstract

Local and global flow structures as well as transfer and transport of a passive scalar from a circular colony of uniformly distributed cylindrical vegetation are investigated at Re = 2100. The number of cylinders in the colony is varied from 1 to 284 yielding solid fraction of 0.00 < ϕ < 0.65. Three flow regimes are identified: Co-shedding flow regime prevails at low solid fraction where wakes of individual cylinders have minimal interaction. Bleeding-wake flow regime is identified at intermediate solid fraction in which stream-wise bleeding flow delays the formation of colony-scale vortices yielding a steady wake between two separated shear layers. Single-body flow regime is observed at high solid fraction and is accompanied by the commencement of colony-scale vortex shedding. As the solid fraction increases, drag and Sherwood number increases linearly and at a reducing rate at low and intermediate solid fractions, respectively, while the net lift is negligible. At high solid fraction, the commencement of colony-scale vortex shedding is accompanied by a jump in lift force and base suction. Both pressure and friction lift/drag increase and decrease with increase in solid fraction, respectively, towards the value experienced by a solid cylinder. Sherwood number decays exponentially towards the value experienced by a solid cylinder at high solid fraction. Colonies at intermediate solid fraction exhibit the highest scalar transfer but weakest transport (diffusion) in their near field wake. Scalar transfer in colonies with high solid fraction deteriorates with increase in solid fraction yielding less scalar concentration in their downstream wake.

Flow-induced rearrangement of a poroelastic cluster

“…The increase and subsequent decrease in the cluster drag with respect to the solid fraction has been generally observed for arrays of static cylinders over a wide range of the Reynolds number (Chang & Constantinescu 2015;Taddei et al 2016;Tang et al 2019Tang et al , 2020Kingora & Sadat 2022). However, less is known about the fluid-dynamic mechanism responsible for the presence of an optimal porosity that maximises the cluster drag.…”

“…However, as illustrated in figure 7, the periodic vortex shedding does not occur behind our poroelastic clusters at low Re. In addition, Kingora & Sadat (2022) employed a physical concept known as sheltering effect, which is similar to the effect of hydrodynamic blockage in our study, in order to analyse the spatial variation of fluid forces depending on the cylinder locations. However, the sheltering effect indicates a decrease in mean flow within the cylinder array, without specifically addressing the hydrodynamic interaction between multiple bodies by strong viscous diffusion, and it was not adopted to explain the drag experienced by the entire cylinder array.…”

“…Accordingly, at the optimal solid fraction for the peak F * x , the cluster takes advantage of the hydrodynamic blockage by maximising the aerodynamic drag. The mechanism underlying the appearance of an optimal φ, which has been ascribed different explanations in various investigations (Chang & Constantinescu 2015;Tang et al 2020;Kingora & Sadat 2022), can be integrated into the principle of the optimal degree of hydrodynamic blockage. For example, the decrease in the optimal φ accompanied by the reduction in Re d , which was reported by Tang et al (2020) for a rectangular cluster of stationary cylinders, can be explained by an intensification of the hydrodynamic blockage with decreasing Re d .…”

“…The positions of the cylinders are determined such that they are located as evenly as possible, following the approach of Nicolle & Eames (2011). The porosity of the model is represented by the solid fraction , which indicates the portion of the area occupied by the cylinders within the circular boundary of the cluster (Nicolle & Eames 2011; Chang & Constantinescu 2015; Taddei, Manes & Ganapathisubramani 2016; Kingora & Sadat 2022). By definition, increases with , and corresponds to an impervious cylinder of diameter .…”

Experimental Study on Influence of Different Patterns of an Emergent Vegetation Patch on the Flow Field and Scour/Deposition Processes in the Wake Region

“…The data presented in their study demonstrated a logarithmic decrease in bleeding velocities as canopy density increased. Kingora and Sadat (2022) investigated the flow through a group of cylinders at the stem scale numerically. Their findings demonstrated a monotonic decrease in drag force exerted on individual members as the solid fraction increased.…”