Thermally-driven vortex resulting from the linear heat wires of different shapes under cross wind
TL;DR: In this article, the authors present an experimental study of the thermally-driven vortex induced by the linear heat wire under cross wind, where the straight, C-and S-shape wires were designed to simulate the fire front of different shapes and a wide range of heat release rate per length and wind speed were used to test the critical conditions under which vortex flows occur.
About: This article is published in Applied Thermal Engineering.The article was published on 2019-12-25. It has received 3 citations till now. The article focuses on the topics: Vortex & Vorticity.
Citations
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TL;DR: In this article , the authors used a long narrow fire source placed parallel to the wind (parallel arrangement); the results were compared with those of previous experiments where the fire source was placed perpendicular to wind (perpendicular arrangement).
1 citations
TL;DR: In this article , the effect of the distance between the burner rim and table's edge, the wind speed and the heat release rate (HRR) on the linear flame was investigated by experimental and numerical simulations.
01 Mar 2013
TL;DR: In this paper, it was shown that counter-rotating vortex pairs (CVPs) formed along and just downwind of a flame were occasionally shed downwind, and these vortices were a CVP of the plume of the flame.
Abstract: One of the formation mechanisms of fire whirls, which often occur in a cross flow downwind of a fire, was studied experimentally in a wind tunnel using a flow visualisation technique. We observed that vortices forming along and just downwind of a flame were occasionally shed downwind. Such vortices differed markedly from wake vortices, which occurred downwind of the flame and exhibited periodic shedding behaviour in the downwind direction. We demonstrated that these vortices were a counter-rotating vortex pair (CVP) of the plume of the flame. This result suggests that the CVP of a large fire is a possible origin of the fire whirls that occur downwind of a fire area and are shed downwind.
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TL;DR: In this article, a fire whirl from a liquid-fuel pool (acetone) is formed at the center of a rotating screen which imparts a controlled angular momentum to the ambient air.
Abstract: A fire whirl from a liquid-fuel pool (acetone) is formed at the center of a rotating screen which imparts a controlled angular momentum to the ambient air. Measurements show that outside of the core the fluid motion is that of a free vortex. A hot-wire method of measurement of the radial temperature distribution is developed. The temperature distribution shows that the fire whirl consists of a rotating cylinder, fuel rich inside, lean outside. The turbulent plume theory is extended to include combustion and angular momentum. This theory checks the experimental results and provides: o 1. The turbulent mixing coefficient decreases with increasing angular momentum, as is to be expected. 2. The turbulent mixing coefficient increases with elevation above the ground. This effect was not expected. Its cause remains unknown, although it may be in some way related to the vertex-jump (vortex breakdown) phenomena which may be required if the whirl is to satisfy both ground-level and “high”-altitude boundary conditions.
175 citations
TL;DR: In this paper, the authors measured the flame length, velocity, temperature, and mass flux for line fires in a very similar manner to axisymmetric systems and found that the air entrainment coefficient for non-reacting, buoyant plume region in the Boussinesq approximation and assuming Gaussian distributions for horizontal velocity and temperature is 0.13.
113 citations
TL;DR: In this article, three types of scale-models, with scaling ratios of 1 235, 1 2500, and 1 4837, corresponding to three actual fire whirls (prototypes) were designed in the laboratory.
112 citations
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TL;DR: In this article, a scaling law that predicts the critical lateral wind velocity was developed and validated by various data including scale-model experiments by other researchers and real urban fire whirls, and a dimensional analysis was conducted to understand the effect of flow circulation on the increase in flame height.
95 citations
01 Jan 2007
TL;DR: In this article, an experimental and methodological investigation on the behaviors of square fire arrays which are composed of 3.5 to 7.7 n-heptane fires initiated from fuel pans of 5 cm in diameter and 2 cm in height is presented.
Abstract: This paper gives an experimental and methodological investigation on the behaviors of square fire arrays which are composed of 3 × 3 to 7 × 7 n-heptane fires initiated from fuel pans of 5 cm in diameter and 2 cm in height. It is intended to develop a burn-out time (BOT) data analysis method to analyze the interaction effects (which may induce fire merging and fire whirls) among the multiple fires. In 26 fire tests the fire point spacing D varied from 20 to 50 cm for each array size and in several cases shear flow was added from one side of the array. By considering the flame height L a reasonable critical condition for initiation of fire merging was implied to be D/L = 0.29 − 0.34, which is independent of the fire array size and fire point spacing. By burn-out time data the Interaction index I (m) and Interaction link index A (m, n) were defined to characterize the fire interactions. The assumptions essential to solve the equation system of I (m) = ∑n A (n, m) were examined in detail, whereby the equation system was solved. The analysis showed that the burn-out time data analysis realizes a quantitatively reasonable comparison of the fire interaction effects, thus indicating that it is reasonable to regard the burn-out time as a measure for the average burning rate for each specific fire point. An apparent criterion of BOT(m)/BOTR = 0.5 was summarized to identify whether any fire point m will be completely involved in fire merging (where BOTR is the burn-out time of the free burning reference fire point). It was implied that the interaction effect imposed on any fire is mainly ascribed to its adjacent four fires. The effects of shear flow to fire burning and occurrences of fire whirls were also discussed.
88 citations