Largeeddy simulation was used to model turbulent atmospheric surface layer (ASL) flow over canopies composed of streamwisealigned rows of synthetic trees of height,
 Award ID(s):
 1753200
 NSFPAR ID:
 10407280
 Date Published:
 Journal Name:
 Physics of Fluids
 Volume:
 34
 Issue:
 6
 ISSN:
 10706631
 Page Range / eLocation ID:
 066601
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
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, and systematically arranged to quantify the response to variable streamwise spacing,$h$ , and spanwise spacing,$\delta _1$ , between adjacent trees. The response to spanwise and streamwise heterogeneity has, indeed, been the topic of a sustained research effort: the former resulting in formation of Reynoldsaveraged counterrotating secondary cells, the latter associated with the$\delta _2$  and$k$ type response. No study has addressed the confluence of both, and results herein show secondary flow polarity reversal across ‘critical’ values of$d$ and$\delta _1$ . For$\delta _2$ and$\delta _2/\delta \lesssim 1$ , where$\gtrsim 2$ is the flow depth, the counterrotating secondary cells are aligned such that upwelling and downwelling, respectively, occurs above the elements. The streamwise spacing$\delta$ regulates this transition, with secondary cell reversal occurring first for the largest$\delta _1$ type cases, as elevated turbulence production within the canopy necessitates entrainment of fluid from aloft. The results are interpreted through the lens of a benchmark prognostic closure for effective aerodynamic roughness,$k$ , where$z_{0,{Eff.}} = \alpha \sigma _h$ is a proportionality constant and$\alpha$ is height root mean square. We report$\sigma _h$ , the value reported over many decades for a broad range of rough surfaces, for$\alpha \approx 10^{1}$ type cases at small$k$ , whereas the transition to$\delta _2$ type arrangements necessitates larger$d$ . Though preliminary, results highlight the nontrivial response to variation of streamwise and spanwise spacing.$\delta _2$ 
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