Abstract
The influence of the model drag coefficient on prediction accuracy of flows past emergent vegetation canopies by a classical canopy model has been examined. Two types of numerical simulations are carried out: The preliminary analysis based on a two-dimensional immersed boundary method gives an estimate of the spatial distribution of the drag coefficient over the vegetation canopy of the target flow. The estimated drag coefficient is introduced into the main analysis where a three-dimensional large-eddy simulation (LES) together with the canopy model is employed. The prediction accuracy of the main analysis is discussed against the corresponding experimental data and another LES result with a uniform drag coefficient in the canopy. The present LES with the estimated drag coefficient shows an improved prediction especially on stagnation phenomena at the leading edge of the vegetation patches. The improvement, however, is found mainly at the time-averaged flow level only. This is because the estimated drag coefficient is obtained from the time-averaged flow and does not reflect the instantaneous flow features directly.
