Keywords

Ash modelling; Post-fire erosion; CFDEM; Wind tunnel

Start Date

16-9-2020 1:40 PM

End Date

16-9-2020 2:00 PM

Abstract

Wildfires are gradually becoming a more recurrent phenomenon worldwide, impacting local environment and, ultimately, human health due to the production of smoke and ash during the combustion process. Although still largely unstudied, it is known that wind plays a major role in post-fire ash erosion and transportation. In this context, the main objective of this work is to develop a high-resolution CFD model capable to assess the influence of wind in ash mobilization. To accomplish this goal, the modelling setup composed by OpenFOAM and LIGGGHTS (LAMMPS Improved for General Granular and Granular Heat Transfer Simulations), coupling for air flow and particle simulation respectively, was used. Air flow was simulated using turbulence model K-Epsilon RNG and LIGGGHTS particles are modeled as soft spheres. To better simulate field ash, a comparative analysis between singular and multiple spheres particles was performed. Modelled results were compared with measured data from experiments conducted in wind tunnel, to evaluate the model performance. The experiments aim to assess the ash mass loss during a three-minute time interval, using Pine ash samples collected from Loriga wildfire of 24 August 2018. Both experimental and modeling results show a similar behavior, whereas most of the ash is eroded during the first seconds of the trial (around 20%). During the remaining time, if there are no high air velocity fluctuations, ash quantity remains stationary. This similarity between the two approaches is better verified in multi-spherical particles and in spherical particles with rolling friction, which are more representative of real ash shape. The application of CFD tools is particularly relevant to assess the effectiveness of mitigation measures, which may be difficult to quantify with wind tunnel experiments.

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Sep 16th, 1:40 PM Sep 16th, 2:00 PM

What are the impacts of post-fire ash mobilization by wind erosion: physical and numerical modelling

Wildfires are gradually becoming a more recurrent phenomenon worldwide, impacting local environment and, ultimately, human health due to the production of smoke and ash during the combustion process. Although still largely unstudied, it is known that wind plays a major role in post-fire ash erosion and transportation. In this context, the main objective of this work is to develop a high-resolution CFD model capable to assess the influence of wind in ash mobilization. To accomplish this goal, the modelling setup composed by OpenFOAM and LIGGGHTS (LAMMPS Improved for General Granular and Granular Heat Transfer Simulations), coupling for air flow and particle simulation respectively, was used. Air flow was simulated using turbulence model K-Epsilon RNG and LIGGGHTS particles are modeled as soft spheres. To better simulate field ash, a comparative analysis between singular and multiple spheres particles was performed. Modelled results were compared with measured data from experiments conducted in wind tunnel, to evaluate the model performance. The experiments aim to assess the ash mass loss during a three-minute time interval, using Pine ash samples collected from Loriga wildfire of 24 August 2018. Both experimental and modeling results show a similar behavior, whereas most of the ash is eroded during the first seconds of the trial (around 20%). During the remaining time, if there are no high air velocity fluctuations, ash quantity remains stationary. This similarity between the two approaches is better verified in multi-spherical particles and in spherical particles with rolling friction, which are more representative of real ash shape. The application of CFD tools is particularly relevant to assess the effectiveness of mitigation measures, which may be difficult to quantify with wind tunnel experiments.