Spatial Heterogeneity Shapes Turbulence in Vegetated Canopy Flows

Vegetated canopy flows are characterized by aggregate momentum absorption and the formation of spatially complex coherent features shaped by canopy structure. A series of wind tunnel experiments were performed at Portland State University to quantify the role of individual and patch scale heterogeneity on shaping vegetated canopy flows. Reduced scale canopy models were manufactured from high porosity reticulated foam and organized into homogeneous canopies with uniform structure and heterogeneous canopies modeled after old growth forest stands. Patch-scale heterogeneity was introduced with regular gaps between canopy sections as well as snag cases where the vegetated layer was removed. Instantaneous measurements of the flow through and above the canopies were obtained from vertical transects with two time-synchronized hot wire anemometers. Canopy structure is quantified through a lacunarity-based heterogeneity index and linked to dominant physical length scales in each canopy arrangement. Turbulent flow statistics reveal canopy spatial heterogeneity drives fluid dynamics across multiple scales. Velocity profiles are shaped by the particular arrangement of individual trees within a stand as well patch-scale gaps and snags. The effect of canopy structure on high-order turbulence statistics and the formation of canopy-specific flow structures will be detailed in presentation.