FLUID MECHANICS

摘要

Experimental measurements and numerical simulations are carried out to determine the hydrodynamics induced by suspended canopies of limited width and height for canopies with six different densities and canopy element arrangements and two different upstream velocities. Measurements of velocity are obtained using acoustic Doppler velocimetry and the drag force via a load cell. Numerical simulation results using OpenFOAM agree very well with the experimental data and are used to investigate the generated flow fields in detail. The bulk features of the flow are similar to those of other canopies, including emergent and submerged canopies, but the finite dimensions of the canopy results in flow patterns that differ from suspended canopies of essentially infinite width. The detailed hydrodynamics of the flow are controlled by the blockage of the suspended canopy which depends both on the canopy density and the lateral spacing between consecutive longitudinal rows of canopy elements. Increased flow blockage results in increases in the drag coefficient from 0.72 to 1.4, reduction in the flow rate inside the canopy from 58 to 98 % (of the diverted flow, 20-43 % is diverted below the canopy) and increases in the steady wake zone length from 0.6 to 4 times the canopy length. Flow blockage has relatively little effect on the length of the upstream adjustment and total wake zones at 1.09 and 7 times the canopy length respectively. The flow also depends only weakly on the upstream velocity.