Turbulent fountains in an open chamber
Turbulent fountains in an open chamber
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DOI：
10.1017/s0022112090002099
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发表时间：
1990-03
影响因子：
3.7
通讯作者：
W. Baines;J. S. Turner;I. Campbell
中科院分区：
文献类型：
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作者：
W. Baines;J. S. Turner;I. Campbell
本文从实验和理论两方面研究了均质流体底部向上注入稠密流体所产生的流动和密度分布。轴对称源和线源都已经使用小规模的实验室实验进行了研究，在实验中将盐水注入到淡水罐中。以这种方式形成的湍流喷泉上升到与流入的弗劳德数相关的最大高度，然后福尔斯回落并沿地板沿着展开。继续流入以类似于Baines & Turner（1969）的“羽流填充箱模型”的方式建立稳定的分层，该模型是对本工作的补充。这里考虑的喷泉流具有重要的新特征，即流入的体积是显著的，因此“开放”容器中的流体的总体积随时间增加。演化由从周围环境进入喷泉的夹带速率决定，这是通过实验直接发现的。流体再次夹带到喷泉中持续地改变在喷泉顶部的水平面以下的腔室底部处收集的混合流体中的密度分布，并且控制标记流体的“前沿”的上升速率。喷泉的顶部随时间线性上升，对于轴对称喷泉，实验和理论都表明其上升速率接近流入引起的自由表面上升速率的一半。因此，在一定的时间，前面上升超过喷泉的顶部。一旦腔室底部的混合流体上升到喷泉上方，其密度分布保持不变。的前端速度，喷泉高度和密度分布都已获得作为时间的函数，使用的理论是在很大范围内的输入弗劳德数与实验结果吻合得很好。对于线喷泉，由于不稳定性，导致流动从对称状态不规则地切换到仅在一侧发生向下流动且最大高度较小的状态，因此结果不太精确。最后，我们讨论的应用程序的动机的工作，特别是分层的混合层的岩浆房从下面补充的发展，和动态相同，但倒置的问题，通过位于屋顶附近的管道加热大型建筑物。
The flow and density distribution produced by injecting dense fluid upwards at the bottom of a homogeneous fluid have been investigated experimentally and theoretically. Both axisymmetric and line sources have been studied using small-scale laboratory experiments in which salt water is injected into a tank of fresh water. The turbulent fountain formed in this way rises to a maximum height which can be related to the Froude number of the inflow, and then falls back and spreads out along the floor. Continuing the inflow builds up a stable stratification in a similar manner to that discussed earlier for the ‘plume filling box model’ of Baines & Turner (1969) which is complementary to the present work. The fountain flows considered here have the important new feature that the volume of the inflow is significant, so the total volume of fluid in the ‘open’ container increases with time. The evolution is determined by the rate of entrainment into the fountain from its surroundings, which is found directly by experiment. Re-entrainment of fluid into the fountain continually changes the density profile in the mixed fluid collecting at the bottom of the chamber below the level of the fountain top, and controls the rate of rise of a ‘front’ of marked fluid. The top of the fountain rises linearly in time, at a rate which, for axisymmetric fountains, has been shown both experimentally and theoretically to be close to half the rate of rise of the free surface due to the inflow. Thus at a certain time the front rises above the top of the fountain. Once the mixed fluid at the bottom of the chamber has risen above the fountain its density profile remains unchanged. The front velocity, the fountain height and the density profile have all been obtained as functions of time using a theory which is in good agreement with the experimental results for a large range of input Froude numbers. For line fountains the results are less precise owing to an instability which causes the flow to switch irregularly from a symmetrical state to one in which the downflow occurs on one side only, and with a smaller maximum height. In concluding we discuss the applications which motivated the work, particularly the development of a stratified hybrid layer in magma chambers replenished from below, and the dynamically identical, but inverted problem of heating large buildings through ducts located near the roof.