Impact of reduced near‐field entrainment of overpressured volcanic jets on plume development
Impact of reduced near‐field entrainment of overpressured volcanic jets on plume development
复制标题
超压火山喷流近场夹带减少对羽流发展的影响
DOI：
10.1029/2011jb008862
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发表时间：
2012
影响因子：
--
通讯作者：
L. Mastin
中科院分区：
文献类型：
--
作者：
F. Saffaraval;S. Solovitz;D. Ogden;L. Mastin
[1]通常使用一维分析模型来研究火山羽流，该模型使用经验卷吸比来封闭方程。虽然该比值通常被视为常数，但由于流动发展和超压条件，其在喷口附近的值显著降低。为了提高这些模型的准确性，进行了一系列的实验，使用粒子图像测速仪，高精度，全场速度测量技术。实验考虑了雷诺数高达467，000和出口压力高达2.93倍大气压的高速射流。出口气体密度也从0.18到1.4倍的空气。对测得的速度进行积分以直接确定夹带。对于出口压力接近大气压的射流，在距离出口20个直径处，夹带比完全发展的水平小约30%。在近三倍的大气压力下，夹带是60%less.These结果被引入到Plumeria，一个一维羽流模式，检查减少夹带的影响。最大柱高仅略有修改，但崩溃的临界半径显着减少，在中等喷发压力下减少了近2倍。
[1] Volcanic plumes are often studied using one-dimensional analytical models, which use an empirical entrainment ratio to close the equations. Although this ratio is typically treated as constant, its value near the vent is significantly reduced due to flow development and overpressured conditions. To improve the accuracy of these models, a series of experiments was performed using particle image velocimetry, a high-accuracy, full-field velocity measurement technique. Experiments considered a high-speed jet with Reynolds numbers up to 467,000 and exit pressures up to 2.93 times atmospheric. Exit gas densities were also varied from 0.18 to 1.4 times that of air. The measured velocity was integrated to determine entrainment directly. For jets with exit pressures near atmospheric, entrainment was approximately 30% less than the fully developed level at 20 diameters from the exit. At pressures nearly three times that of the atmosphere, entrainment was 60% less. These results were introduced into Plumeria, a one-dimensional plume model, to examine the impact of reduced entrainment. The maximum column height was only slightly modified, but the critical radius for collapse was significantly reduced, decreasing by nearly a factor of two at moderate eruptive pressures.