Investigating Buoyant Plume Dynamics Induced by Localized Fire‐Simulated Heating Over Plant Canopies Using LES

Plume interaction with a forest canopy results in flow features distinct from those in grasslands. Here, we model the turbulence dynamics of a buoyant plume in a homogeneous plant canopy with a crosswind using Large‐Eddy Simulations. As the plume interacts with the crosswind, we observe increased vorticity at the windward and tilted hair‐pin‐like vortical structures on the leeward sides. Strong rotational cores, representing counter‐rotating vortex pairs (CVPs), form as the flow twists and spirals into the leeward side of the buoyancy source. Flow patterns aloft exhibit helical motions as the CVPs propagate downstream, trailing the plume. We also simulate a no‐canopy environment for comparison. In the canopy case, the plume tilts less steeply near the source due to the canopy drag and its leeward side is marked by flow recirculation, which obstructs the approaching upstream flow. Moreover, the plume transition to the bent‐over phase is delayed and oscillations in the far‐field mean plume centerline are more damped. The spatial organization of momentum‐flux events also differs between the two environments. Upstream of the plume centerline, there is downward momentum transfer primarily via ejections above and sweeps within the canopy. On the leeward side, counter‐gradient motions (outward interactions) prevail in transferring momentum away from the buoyancy source. Contrarily, in the no‐canopy environment, counter‐gradient motions near the surface are wedged between ejection‐ and sweep‐dominated regions on the upstream and downstream sides, respectively. Insights into plume behavior in canopy versus no‐canopy environments are vital for comparing with experiments and refining fire‐behavior and plume‐rise models.