ON NUMERICAL PREDICTION OF VEGETATED FLOWS WITH UNDISTURBED-FLOW EFFECTS

Abstract

 A drag-force model is essential in practical predictions of flows around vegetation/urban canopies since it is too prohibitive to resolve details of the canopy elements and associated fluid motions, especially in environmental and geophysical applications. However, the macroscopic model has a clear bottleneck: how one can obtain a proper distribution of drag coefficient for practical applications. Here particular attention is paid to undisturbed flow as a representative velocity scale required in the empirical formulation relating the drag force to an obstacle with the flow around it. The present study clearly has shown that (i) employing the undisturbed flow as the representative velocity can improve the prediction accuracy, and (ii) the prediction accuracy of the drag-force model becomes deteriorated in nonequilibrium flows. While direct evaluation of the undisturbed flow performed in the current study is impractical in general, the approaching velocity that one can obtain from the disturbed flow field has presented its validity as an alternative to the undisturbed flow to some extent.