arXiv subjects

Ajinkya Desai

Publications and source records attributed to Ajinkya Desai.

3 recordsLinked to original sources

arXiv2026

Scaling analysis for buoyant plumes over wildland fires

Tracking the structure and geometric properties of a buoyant plume in crosswind is critical for managing smoke hazards and improving disaster mitigation decision-making. Plume features, such as tilt angle, height, and curvature changes, are impacted by multiple forcing parameters, with canopy-induced turbulence patterns adding complexity. This study examines how these parameters, reduced to fewer dimensionless groups, affect the plume centerline slope, both near the surface and in the far field. Results from large-eddy simulations, conducted in both canopy and no-canopy environments, explore power-law dependencies, based on prior formulations, between the slopes and dimensionless groups describing the (1) relative strength of the buoyancy source to ambient wind forcing, (2) plume turbulence intensity relative to upstream turbulence, and (3) canopy density and height. Near-surface slopes are an order of magnitude higher in the canopy cases, although their sensitivity to group (1) is similar across both environments. In the canopy cases, the near-surface slope follows a one-fourth power-law dependence with group (2). This effect is absent in the no-canopy case, reflecting differences in the momentum-flux structure near the source. Moreover, the canopy aerodynamic effects delay the plume transition from the rise phase into the far-field, bent-over phase; however, canopy effects diminish as buoyancy source strength increases. The near-surface plume slope exhibits a more complex dependence on canopy geometry, increasing almost linearly with the canopy height but showing weaker sensitivity to canopy drag. Our findings support the development of scaling laws for plume structures across varied vegetative landscapes and inform improved predictive modeling efforts.

physics.ao-ph↗

arXiv2025

Impact of Forest Canopy Structure on Buoyant Plume Dynamics During Wildland Fires

This study investigates the influence of forest canopy heterogeneity on buoyant plume dynamics resulting from surface thermal anomalies representing wildland fires, utilizing Large Eddy Simulation (LES). The Parallelized Large-Eddy Simulation Model (PALM) was employed to simulate six canopy configurations: no canopy, homogeneous canopy, external plume-edge canopy, internal plume-edge canopy, 100 m gap canopy, and 200 m gap canopy. Each configuration was analyzed with and without a static surface heat flux patch of 5000 $\mathrm{W \cdot m^{-2}}$, resulting in a resting buoyant plume. Simulations were conducted under three crosswind speeds: 0, 5, and 10 $\mathrm{m \cdot s^{-1}}$. Results show that canopy structure significantly modifies plume behavior, mean flow, and turbulent kinetic energy (TKE) budgets. Plume updraft speed and tilt varied with canopy configuration and crosswind speed. Pressure gradients associated with plume updrafts were modified based on the canopy configuration, resulting in varying crosswind speed reductions at the plume region. Strong momentum absorption was observed above the canopy for the crosswind cases, with the greatest enhancement in the gap canopies. Momentum injection from below the canopy due to the heat source was also observed, resulting in plume structure modulation based on canopy configuration. TKE was found to be the largest in the gap canopy configurations. TKE budget analysis revealed that buoyant production dominated over shear production. At the center of the heat patch, the gap canopy configurations showed enhanced buoyancy within the gap. Spatial distributions demonstrated increased shear production at the interface between the plume and crosswind.

physics.flu-dyn↗

arXiv2025

Investigating Buoyant Plume Dynamics Induced by Localized Fire-Simulated Heating over Plant Canopies Using LES

The interaction of a buoyant plume with a plant canopy results in turbulent flow features distinct from those in a grassland environment. In this work, 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 edge and tilted hair-pin-like vortical structures on the leeward side. Strong rotational cores, representing counter-rotating vortex pairs (CVPs), form as the flow twists and spirals into the leeward side of the buoyancy source from either side. Flow patterns aloft exhibit helical motions as the CVPs aloft propagate downstream, trailing the plume. We also simulate a no-canopy environment to facilitate comparison. The plume tilts less steeply near the source in the canopy case due to the canopy drag and its leeward side is marked by flow recirculation near the canopy top, which obstructs the upstream flow as it approaches. Moreover, the plume transition from the rise phase to the bent-over phase is delayed due to the canopy's aerodynamic effects and the oscillatory behavior of the far-field mean plume centerline is more damped. Additionally, in the canopy environment, there is downward momentum transfer primarily via ejections above the canopy and sweeps within the canopy space, upstream of the plume centerline. On the leeward side, counter-gradient motions play a significant role in transferring momentum away from the buoyancy source, with outward interactions being most dominant. Contrarily, in the no-canopy environment, counter-gradient motions near the surface are flanked upstream by an ejection-dominated region and downstream by a sweep-dominated region. Insights into the distinct plume behavior in canopy vs. no-canopy environments are vital for comparing with experiments and refining fire behavior or plume rise models.

physics.ao-ph↗