Turbulent Flow through Idealized Emergent Vegetation

Abstract

This paper presents results of several large-eddy simulations ͑LES͒ of turbulent flow in an open channel through staggered arrays of rigid, emergent cylinders, which can be regarded as idealized vegetation. In this study, two cylinder Reynolds numbers, R D = 1 , 340 and R D = 500, and three vegetation densities are considered. The LES of the lowest density and at R D = 1 , 340 corresponds to a recently completed laboratory experiment, the data of which is used to validate the simulations. Fairly good agreement between calculated and measured first-and second-order statistics along measurement profiles is found, confirming the accuracy of the simulations. The high resolution of the simulations enables an explicit calculation of drag forces, decomposed into pressure and friction drag, that are exerted on the cylinders. The effect of the cylinder Reynolds number and the cylinder density on the drag and hence on the flow resistance is quantified and in agreement with previous experimental studies. Turbulence structures are visualized through instantaneous pressure fluctuations, isosurfaces of the Q-criterion and contours of vertical vorticity in horizontal planes. Analysis of velocity time signals and distributions of drag and lift forces over time reveals that flow and turbulence are more influenced by the vegetation density than by the cylinder Reynolds number.

Does the canopy mixing layer model apply to highly flexible aquatic vegetation? Insights from numerical modelling

“…7a, b) indicate that the turbulence predominantly follows the expected Kolmogorov decay rate, indicating that all the scales of interest lie within the inertial subrange and that the model accurately reproduces the turbulent processes with this range, with minimal impact of numerical diffusion or energy dissipation due to the SGS model [81,82]. As discussed in Sect.…”

High-resolution numerical modelling of flow—vegetation interactions

“…Furthermore, using this Although, the initial application of the model has been on relatively simple canopies, the new methodology presented here enables investigation of flow through complex canopies across a wide range of plant forms. This is essential as natural macrophyte canopies do not conform to the idealised canopy configurations traditionally studied (Dunn et al 1996, Stoesser et al 2010 and it is possible that different turbulent processes dominate in the nonidealised case. The application of the N-pendula model permits the investigation of turbulent energy extraction, and thus the effect on the mean flow conditions through realistic canopies.…”

“…Subsequent work has developed this analysis and begun to use larger domains, enabling larger patch-scale analysis at stem-scale resolution. Stoesser et al (2010) undertook LES experiments on a patch of emergent vegetation using a combination of high resolution Cartesian and curvilinear grids. They used a range of different vegetation densities and were able to investigate the structural changes to wake turbulence patterns caused by changes in vegetation density and found that these changes had a significant effect on turbulence statistics and flow resistance.…”

Feasibility of the Porous Zone Approach to Modelling Vegetation in CFD

“…King et al (2012) propose a new k − ε turbulence model for inclusion in a Computational Fluid Dynamics (CFD) model that takes the effects of vegetation into account. Alternatively, Stoesser et al (2010) directly simulated flow through vegetation stems using Large Eddy Simulation.…”