The Ceiling Height of Wildland Fire Plumes in Sheared Boundary Layer Flow

Abstract

Radar observations from a prescribed fire experiment reveal a large-scale, billow-like vorticity pair associated with the plume head at the onset of plume bending. The bending confines the ceiling height of the plume, delaying its smoke dispersion and increasing fire spotting risks. This study aims to investigate the onset of plume bending in a sheared crossflow and stratified atmospheric conditions, providing insights into smoke dispersion and fire behavior. Large Eddy Simulations (LES) using the Cloud Model 1 (CM1) are conducted to simulate the observed development of plume structure and its associated dynamical fields, with particular focus on the plume head and its evolution from initial plume development under different fire intensities and atmospheric boundary layer (ABL) conditions. A scaling analysis of plume ceiling height is proposed based on a modified Byram's convective number that accounts for sheared crossflow. The proposed scaling agrees well with the LES results, highlighting the critical roles of shear and stratification in controlling plume dynamics.