Large-Eddy Simulation of Coherent Flow Structures within a Cubical Canopy |
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| Authors: | Atsushi Inagaki Marieta Cristina L Castillo Yoshimi Yamashita Manabu Kanda Hiroshi Takimoto |
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| Institution: | 1.Department of International Development Engineering,Tokyo Institute of Technology,Tokyo,Japan |
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| Abstract: | Instantaneous flow structures “within” a cubical canopy are investigated via large-eddy simulation. The main topics of interest
are, (1) large-scale coherent flow structures within a cubical canopy, (2) how the structures are coupled with the turbulent
organized structures (TOS) above them, and (3) the classification and quantification of representative instantaneous flow
patterns within a street canyon in relation to the coherent structures. We use a large numerical domain (2,560 m × 2,560 m ×
1,710 m) with a fine spatial resolution (2.5 m), thereby simulating a complete daytime atmospheric boundary layer (ABL), as
well as explicitly resolving a regular array of cubes (40 m in height) at the surface. A typical urban ABL is numerically
modelled. In this situation, the constant heat supply from roof and floor surfaces sustains a convective mixed layer as a
whole, but strong wind shear near the canopy top maintains the surface layer nearly neutral. The results reveal large coherent
structures in both the velocity and temperature fields “within” the canopy layer. These structures are much larger than the
cubes, and their shapes and locations are shown to be closely related to the TOS above them. We classify the instantaneous
flow patterns in a cavity, specifically focusing on two characteristic flow patterns: flushing and cavity-eddy events. Flushing
indicates a strong upward motion, while a cavity eddy is characterized by a dominant vortical motion within a single cavity.
Flushing is clearly correlated with the TOS above, occurring frequently beneath low-momentum streaks. The instantaneous momentum
and heat transport within and above a cavity due to flushing and cavity-eddy events are also quantified. |
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