Drag coefficient and plant form response to wind speed in three plant species: Burning Bush (<i>Euonymus alatus</i>), Colorado Blue Spruce (<i>Picea pungens</i> glauca.), and Fountain Grass (<i>Pennisetum setaceum</i>)

Abstract

Whole‐plant drag coefficients ( C d ) for three plant species: Burning Bush ( Euonymus alatus ), Colorado Blue Spruce ( Picea pungens glauca.), and Fountain Grass ( Pennisetum setaceum ) in five different porosity configurations were developed from force versus wind speed data collected with a force balance in a recirculating wind tunnel. The average C d for the Burning Bush, Colorado Spruce, and Fountain Grass in their untrimmed forms were 0.42 (±0.03), 0.39 (±0.04), and 0.34 (±0.06), respectively. Drag curves ( C d versus flow Reynolds number ( R e ) function) for the Burning Bush and Colorado Spruce were found to exhibit, for the lower porosity configurations, a rise to a maximum around flow Reynolds numbers ( R e = ρ u h h /ν) of 2 × 10 5 . Fountain Grass C d was shown to be dependent upon R e to values &gt;5 × 10 5 . The Burning Bush and Colorado Spruce plants reduced their drag, upon reaching their maxima, by decreasing their frontal area and increasing their porosity. Maximum C d for these plants occurred at optical porosities of ∼0.20. The Fountain Grass reduced drag at high R e by decreasing frontal area and porosity. The mechanism of drag reduction in Fountain Grass was continual reconfiguration to a more aerodynamic form as evidenced by continual reduction of C d with R e .