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論文
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石井, 哲人 ; 佐藤, 博之 ; 天谷, 賢児 ; 新井, 雅隆
概要:
application/pdf<br />Journal Article<br />The effects of gravity on the fluctuation characteristics of turbulent diffusion flames were experimentally investigated. Super gravity fields were formed using a spin tester. The gravity
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level G was changed from 1 to 20, where G was defined as the value of super gravity per normal gravity. Flame states such as laminar, flickering and turbulent flames were observed under the various conditions of gravity level, G and Reynolds number, Re. The transition from laminar to turbulent and blow out limit were summarized on a G-Re map. Characteristics of turbulent fluctuation were measured by a laser light reflection method. Power spectra and auto-correlations were derived from the signal of laser intensity. As the result, it was found that the turbulent flame was begun to periodic oscillation with increasing the gravity level. Time scale of turbulent fluctuation in the super gravity became long than that in the normal gravity. Spectrum component in power spectrum shifted to the low frequency side when the gravity level became high. And the full width at half-maximum of autocorrelation peak became wider in the super gravity conditions.
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論文
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佐藤, 博之 ; 天谷, 賢児 ; 新井, 雅隆
概要:
application/pdf<br />Journal Article<br />Effect of gravity level on the flickering motion was experimentally investigat
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ed for the propane and propane-hydrogen jet diffusion flames. A centrifuge was used for quantitative measurement of gravity effect, and frequency analysis was performed for the flickering flames. From the result of measurements under various gravity levels, it was clarified that the flickering frequency increased with an increase in the gravity level and it was correlated with two relationships expressed by the Strouhal number and the Froude number. One relationship was St∝Fr^<-0.41> for high Froude numbers (Fr≥100), and the other was St∝Fr^<-0.50> for low Froude numbers (Fr≤100). It meant that the Froude number gave the criterion of the flickering behavior and that flickering frequencies expressed by these two equations were affected by buoyancy in different ways. From the frequency analysis, it was found that oscillations of a flickering flame and a thermal convection around the flame were linked, but the characteristic of each flickering motion was different in the stability of periodicity.
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論文
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佐藤, 博之 ; 天谷, 賢児 ; 新井, 雅隆
概要:
application/pdf<br />Journal Article<br />Quantitative investigation of the gravity effect was performed for acetone and kerosene pool fires. A centrifuge was used to examine the gravity effect. Small-scale pool fires were observed
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under various high gravity fields. Regions of stable flame, puffing flame and irregular oscillatory flame were mapped with the gravity level and pool diameter. Flame height decreased and oscillatory frequency increased with an increase in the gravity level. Behavior of the flame height was agreed quantitatively with the scaling prediction presented by Orloff and Heskestad. Puffing phenomena observed under various gravity fields were summarized with the Strouhal number and Froude number. As the result, we could obtain an empirical equation of St=0.517Fr^<-0.502>. From this equation, puffing frequency could be estimated for a flame of various pool diameter varying from 0.01 to 50 meters.
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