Numerical simulation of the heat-relief capacity of an axisymmetric body in a gas flow

The paper describes a computational experiment and presents the results of numerical modeling of an axisymmetric body with an optimized shape with a minimum aerodynamic drag force as a heat sink in a convective gas flow. The resulting optimized body shape coincides with streamlines, which is the main advantage, since no separation of the flow from the surface is observed in the flow around. Thus, the entire surface area will be the effective surface area of the heat sink, unlike other known body shapes, due to which the temperature of the heat-loaded element placed in the center of the heat sink will decrease.

Floristic shifts in wetlands: the effects of environmental variables on the interaction between Phragmites australis (Common Reed) and Melaleuca ericifolia (Swamp Paperbark)

Over the past 40–50 years, the woody shrub Melaleuca ericifolia has progressively invaded large areas of Phragmites australis in Dowd Morass, a Ramsar-listed, brackish wetland in south-eastern Australia. To understand the processes underlying this shift we grew Phragmites and Melaleuca alone and together under contrasting sediment organic-matter loadings and salinities. To examine if the capacity of Phragmites to aerate the sediment influenced plant interactions, we also dissipated convective gas flow in some Phragmites plants by perforating their stems. Although Phragmites suppressed the growth of Melaleuca under all conditions, Melaleuca persisted. We did not find Phragmites ramets to be more sensitive to salinity than Melaleuca seedlings. Surprisingly Phragmites did not increase sediment redox and was more sensitive to increased organic-matter loading than Melaleuca. These results do not support the notion that colonisation by Melaleuca was facilitated by a decline in Phragmites at higher salinities or through aeration of the sediments by Phragmites. Seedlings of Melaleuca, however, were easily blown over by wind and it is likely that Phragmites stands shelter Melaleuca during establishment. Although our short-term experiment did not show that Melaleuca was a better competitor, differences in seasonal growth patterns may contribute to a shift in competitive abilities over a longer time scale.

Numerical and Experimental Study of Merging Fires in Square Arrays

In large-scale forest fires and city fires, merging fires and fire whirls have often been observed, which cause substantial casualties and property damages. It is important to know particularly where and under what conditions of weather such merging fires and fire whirls appear in cities or forests. However, there have been no adequate answers, since the detailed physical characteristics about them are not fully clarified yet, although previous studies have examined the phenomena of merging flames. Therefore, we have carried out preliminary studies and found that the merged tall fires can enhance the fire spread, and developed a method to analyze burn-out data of fire arrays. If sufficient knowledge can be obtained by relevant experiments and numerical computations, it may be possible to mitigate the damages due to merged fires and fire whirls. The objective of this study is to investigate the merging conditions of fires in square arrays in laboratory experiments and also by CFD numerical simulations, varying the size of square array, inter-fire distance and heat release rate, to judge ‘unmerged’ or ‘merged’ conditions in the fire array. It has been found that the fire merging is dependent on the inter-fire distance in the array and also on the total heat release rate of all fires surrounding the center region of the array. Also found that the experimental and simulated results on the merged and unmerged cases in the fire array, as affected by the total heat release rate and the inter-fire distance, which control the convective gas flow into the array, behave very similarly. Therefore, it can be concluded that the fire merging in array fires are highly based on the convection in the flow field due to fires and can be predicted by simple CFD simulations.