Negatively buoyant projectiles – from weak fountains to heavy vortices
Negatively buoyant projectiles – from weak fountains to heavy vortices
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DOI：
10.1017/s0022112010002508
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发表时间：
2010-07
影响因子：
3.7
通讯作者：
O. J. Myrtroeen;G. Hunt
中科院分区：
文献类型：
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作者：
O. J. Myrtroeen;G. Hunt
本文描述了一个实验研究，以确定有限体积的流体克服浮力垂直向上冲击进入均匀密度的静止环境所达到的最大上升高度zm。在没有密度对比的情况下，释放作为涡环传播，并且垂直轨迹受到粘性效应的限制。在增加释放的源密度时，重力效应限制轨迹并且达到最大上升高度zm。对于这些负浮力释放，zm对喷射流体柱的长度L、喷嘴直径D（= 2 r 0）、分配时间和源降低重力的依赖性通过将盐溶液注入淡水环境中来确定。对于3.4 μ L/D ≥ 9.0，zm/r 0与源参数η = Fr（L/D）成比例，源参数η = Fr（L/D）是有限体积释放的源弗劳德数Fr和长宽比L/D的乘积。我们的研究结果表明，帽的形态，发展以上的源和内诱导的旋涡运动是敏感地依赖于源的条件。此外，还确定了三种上升高度区域：“弱喷泉过渡”、“涡度发展”和“强制释放”区域，每种区域都具有不同的形态和无量纲上升高度对η的依赖关系。
An experimental investigation to establish the maximum rise height zm attained by a finite volume of fluid forced impulsively vertically upwards against its buoyancy into quiescent surroundings of uniform density is described. In the absence of a density contrast, the release propagates as a vortex ring and the vertical trajectory is limited by viscous effects. On increasing the source density of the release, gravitational effects limit the trajectory and a maximum rise height zm is reached. For these negatively buoyant releases, the dependence of zm on the length L of the column of ejected fluid, nozzle diameter D (= 2r0), dispensing time and source reduced gravity is determined by injecting saline solution into a fresh-water environment. For 3.4 ≲ L/D ≲ 9.0, zm/r0 is shown to scale on the source parameter η = Fr(L/D), a product of the source Froude number Fr and the aspect ratio L/D for the finite-volume release. Our results show that the morphology of the cap that develops above the source and the vortical motion induced within are sensitively dependent on the source conditions. Moreover, three rise-height regimes are identified: ‘weak-fountain-transition’, ‘vorticity-development’ and ‘forced-release’ regimes, each with a distinct morphology and dependence of dimensionless rise height on η.