Hydrodynamics of a rigid submerged vegetated flow

In this paper, the local flow and turbulence characteristics of rigid submerged vegetated flow are studied using the double-averaging methodology. Experimental results indicate that the double-averaged streamwise velocity profile above the canopy follows a logarithmic law, while the canopy-induced drag significantly reduces the velocity through the vegetation elements. At the canopy top, an inflection occurs in the velocity profile, implying the existence of the Kelvin–Helmholtz (K–H) instability. The faster-moving fluid above the canopy interacts with the slower-moving fluid within the canopy, creating a strong shear at the canopy top. This induces the Reynolds shear stress, which peaks at the canopy top. The localized accelerated and decelerated flow regions occurring within the canopy produce dispersive shear stress that enhances fluid mixing and momentum transport. The second-order correlation shows the presence of coherent structures at the canopy top due to the K–H instability. The third-order correlation and the quadrant analysis demonstrate that the sweep events dominate the flow in the canopy layer, and the ejection events prevail in the main-flow layer. The turbulent kinetic energy (TKE) fluxes also confirm these findings. The negative streamwise dispersive kinetic energy flux within the canopy suggests that local interactions transport the TKE upstream. The TKE production rate peaks near the canopy top, while the TKE dissipation rate continuously increases within the canopy down to the bed. Higher streamwise spatial fluctuations downstream of the vegetation elements result from the effect of the canopy on the flow.