Direct Numerical Simulation Of Three-dimensional Buoyant Reactive Plume

Buoyant reactive plume is a basic phenomenon of fire, and researching its near-field dynamics is a very important part to understand the fire phenomena. Based on direct numerical simulation (DNS) which doesn't depend on the turbulence and combustion model and instead, directly solve the hydrodynamic equations, the three-dimensional buoyant reactive plumes with low Reynolds number was numerically investigated, and the detailed information of the near-field plume dynamics were obtained. The work in this paper mainly includes four parts as follows:Owing to the large computational account of direct numerical simulation in the three-dimensional combustion problem, the reasonable physical model and boundary conditions in this work were determined, and the dimensionless flow-field was proposed using similarity principle of dynamics, which provided a theoretical basis for the direct numerical simulation of buoyant reactive plumes.Thermal radiation plays a significant role in fire science, but few relative numerical simulations were carried out by researchers before. The information of near field dynamics of buoyant reactive plume, including the vertical structures, temperature, velocity, turbulence fluctuation, entrainment and other characteristics, were contrasted and analyzed under three different radiation magnitude (0%, 10% and 35%) conditions by spatial three-dimensional direct numerical simulation. Quantitative analysis of the influence of radiation on reactive plumes was taken then.In view of fire in plateau area being the hot issue of fire science at present, the direct numerical simulation was used to study buoyant reactive plumes at 2000 meters and 4000 meters above sea level. And the plume's characteristics including the dimensionless of temperature field, vorticity field, turbulence fluctuation, etc were analyzed. At last, the impact of external environment on the reactive plumes, and the characteristics of the buoyant reactive plume in plateau area were determined. The results show that there are some influences on the reaction rate and pulsation period of reactive plume for the low pressures and low oxygen concentrations condition in high altitude areas, which would provide a useful reference for fire test on the plateau.In allusion to the influence of the radiation upon the buoyant reactive plume in the plain area, the influence of different radiation magnitude at high altitude with low pressures and low oxygen concentrations was also studied. At the same time, the influence of radiation on reactive plumes under two different altitude conditions were compared and analyzed.This work was supported by the National Natural Science Foundation of China (50876097), for which the author like to express his gratitude.