Conditional sampling of forest canopy gusts

摘要

Velocity measurements by a two-component laser-Doppler anemometer have been made in a wind-tunnel flow over a forest of aeroelastically scaled model trees. Mean velocity profiles close above three different model canopies exhibit typical 'shear-layer' inflections that are similar, as are the turbulence characteristics, when scaled by characteristic dimensions of the shear layer. A wavelet-based conditional sampling technique is used to generate pseudo-instantaneous flow-field vector maps that are concurrent with significant tree bending events. These diagrams show clear evidence of canopy penetration by coherent gusts. A discussion is offered, of the relationship between the development of coherent gusts and conventional descriptions of mixing layer instability.