Application of the lattice Boltzmann method to thermal explosion development

Abstract

The Lattice Boltzmann Method (LBM) is a relatively new approach within the field of CFD and offers several advantages over traditional continuum based CFD solvers including a high degree of parallelisation and relatively simple boundary conditions. This makes it an attractive potential solution to simulating aspects of fire behaviour. However, at present it has a major disadvantage. It does not handle large changes of temperature, which often create numerical instability. Application of the LBM to reacting flows is an area of current development in the field, and shows promise with respect to application in fire scenarios, although it has not yet developed enough to be able to model a compartment fire. The aim of this work was to develop a full 3D CFD model based on the LBM that could model an aspect of reacting flows. The development of a thermal explosion, and the effect of natural convection on that development, was selected as the area of study. Whilst fundamental work on thermal explosions was done in the 1930’s, there still remains a lot of development to be done; in particular the effect of natural convection on thermal explosions is not sufficiently quantified. This work is novel as very little work has been published using LBM in this area, and the effect of natural convection on the thermal explosion development has been quantified. This was modelled using the Boussinesq approximation to account for buoyancy changes due to temperature and the Frank Kamenetskii theory for thermal explosion development. Both single fireball and two fireballs were examined for Rayleigh numbers in the range 3 7 Ra = 6.10 -6.10 , and the effect was quantified by examination of the ratio of the critical Frank Kamenetskii value under natural convection conditions to the same parameter under no convection conditions. It was found that the ratio increased monotonically with increasing Rayleigh number. The separation distance between the centres for two fireballs was also evaluated. For higher separation distances the effect of natural convection was more profound than for closer separation distances.

Date of Award	May 2013
Original language	English
Supervisor	Paul Joseph (Supervisor) & VASILY NOVOZHILOV (Supervisor)