Dynamical and thermal behavior of depositing firebrands in a turbulent boundary layer*

The motion and deposition of cylindrical shaped firebrands (embers) were investigated by Lagrangian tracking in a turbulent boundary layer, simulated by LES, in a previous study (Anand et al, IJMF, in press, DOI: 10.1016/j.ijmultiphaseflow.2018.07.012). The influence of turbulence on motion of firebrands was explored by calculating their turbulent dispersion and diffusion. Their deposition pattern was quantified by calculating the joint probability density function of their landing position coordinates. The previous study was based on a critical assumption: the firebrand mass was fixed. In the current study, this assumption is relaxed while accounting for thermal behavior of firebrands, e.g., firebrand temperature, which was neglected in the previous study. As hot firebrands fly, they exchange thermal energy with ambient through convection and thermal radiation while losing mass by pyrolysis and char oxidation.  These effects are accounted for by solving mass and energy equations for each firebrand. Influence of turbulence on mass and temperature of firebrands, which are important factors in the ignition of the spot where they land, is investigated.