Impact of gaps on the flow statistics in an emergent rigid canopy

Abstract

High-resolution large eddy simulations and complementary laboratory experiments using particle image velocimetry were performed to provide a detailed quantitative assessment of flow response to gaps in cylinder arrays. The base canopy consists of a dense array of emergent rigid cylinders placed in a regular staggered pattern. The gaps varied in length from [Formula: see text] to 24, in intervals of 4 d, where d is the diameter of the cylinders. The analysis was performed under subcritical conditions with Froude numbers [Formula: see text] and bulk Reynolds numbers [Formula: see text]. Results show that the gaps affect the flow statistics at the upstream and downstream proximity of the canopy. The affected zone was [Formula: see text] for the mean flow and [Formula: see text] for the second-order statistics. Dimensionless time-averaged streamwise velocity within the gap exhibited minor variability with gap spacing; however, in-plane turbulent kinetic energy, k, showed a consistent decay rate when normalized with that at [Formula: see text] from the beginning of the gap. The emergent canopy acts as a passive turbulence generator for the gap flow for practical purposes. The streamwise dependence of k follows an exponential trend within [Formula: see text] and transitions to a power-law at [Formula: see text]. The substantially lower maximum values of k within the gap compared to k within the canopy evidence a limitation of gap measurements representative of canopy flow statistics. We present a base framework for estimating representative in-canopy statistics from measurements in the gap.

Canopy Randomness, Scale, and Stem Size Effects on the Interfacial Transfer Process in Vegetated Flows

“…According to Ranjan et al. (2022), the measuring gap regions affected by the upstream vegetation stems have a short extent. Turbulence strength downstream of the array reaches the maximum value within one unit of the diameter length, 1 d, and then transitions from an exponential to a power‐law decay, quickly dropping back to a minimum value within four units of the diameter length, 4 d, suggesting that the closest two rows of the canopy upstream from the measuring gap would have the highest influence to the flow pattern.…”

On the Effects of Turbulence Modulation Driven by Suspended Sediment Stratification in Emergent Rigid Canopies

“…The numerical domain for both the vegetated and non-vegetated channel flows is similar to that simulated in Ranjan et al (2022). The channel is 15 cm wide and 10 cm high, with staggered array of rigid emergent cylinders of diameter d = 6.25 mm and solid volume fraction ϕ = 0.088, as shown in Figure 3b.…”

“…The simulations were conducted for 12.11 flow-through times (the number of times a fluid parcel is advected through the entire domain during the simulation duration) while the time averaging was done over the last 5.05 flow-through times when the flow had reached a steady state. Ranjan et al (2022) simulated hydrodynamics of a similar canopy and reported the effect of canopy gaps on the mean and higher order statistics. More details of the numerical solver, mesh, and validation of the numerical model is presented in Ranjan et al (2022).…”

“…More details of the numerical solver, mesh, and validation of the numerical model is presented in Ranjan et al. (2022).…”

“…Ranjan et al (2022) simulated hydrodynamics of a similar canopy and reported the effect of canopy gaps on the mean and higher order statistics. More details of the numerical solver, mesh, and validation of the numerical model is presented in Ranjan et al (2022).…”