Closure modeling and direct simulation of vegetation drag in flow through emergent vegetation

This paper presents numerical simulations of flow through emergent vegetation. Two simulation strategies are evaluated, (1) Reynolds‐averaged Navier‐Stokes (RANS)‐ based simulations employing a vegetation closure model and (2) low‐resolution large‐eddy simulation (LES). RANS‐based models offer efficiency in terms of computational resources, however, it is demonstrated herein that the accuracy of RANS models depends strongly on empirical parameters of the corresponding vegetation closure model. The method of low‐resolution LES is an efficient alternative to a fully resolved LES, simulates vegetation drag directly, and does not require empirical parameter input. Predictions of the vegetative flow resistance of emergent vegetation using low‐resolution LES are in fairly good agreement with measurements, in particular for low and moderate vegetation densities. This is because prevailing stream‐ and spanwise‐velocity gradients, vertical velocity profiles, and recirculation zones are calculated with reasonable accuracy.