Time-dependent flows in an emptying filling box
Time-dependent flows in an emptying filling box
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DOI：
10.1017/s0022112004001156
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发表时间：
2004-11
影响因子：
3.7
通讯作者：
N. Kaye;G. Hunt
中科院分区：
文献类型：
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作者：
N. Kaye;G. Hunt
我们研究的瞬态浮力驱动的流动在一个通风的填充盒，是受到持续供应的浮力。一个矩形框被认为是浮力输入表示为湍流羽流，或作为多个非相互作用的羽流，从地板上上升。盒子底部和顶部的开口将内部环境与恒定均匀密度的静态外部环境联系起来。一个理论模型的开发预测，作为时间的函数，密度分层和体积流量通过开口导致的稳定状态。与小规模的模拟实验室实验中，盐溶液和淡水被用来创建密度差的结果进行比较。确定了两个特征时间尺度：填充箱时间（$T_f$），与流体从羽流填充封闭箱所需的时间成比例;以及排出箱时间（$T_d$），与通风箱排出浮力流体所需的时间成比例。流动达到稳定状态的时间尺度取决于这两个时间尺度，这两个时间尺度是箱高度H和横截面积S、“有效”开口面积A^*$以及浮力输入的强度、数量和分布的函数。稳态流动的特征在于这些时间尺度的比值（$\mu\，{=}\，T_d/T_f$），它相当于无量纲的排气口面积$A^*/H^2$。这些流动的一个特征是，对于$\mu\，{>}\，\mu_c$，在初始瞬变过程中，浮力上层的深度可能超过或“过冲”稳定层深度。确定线和点源羽流的$\mu_c$的值，并评估浮力输入分布的发展流的敏感性。
We examine the transient buoyancy-driven flow in a ventilated filling box that is subject to a continuous supply of buoyancy. A rectangular box is considered and the buoyancy input is represented as a turbulent plume, or as multiple non-interacting plumes, rising from the floor. Openings in the base and top of the box link the interior environment with a quiescent exterior environment of constant and uniform density. A theoretical model is developed to predict, as functions of time, the density stratification and the volume flow rate through the openings leading to the steady state. Comparisons are made with the results of small-scale analogue laboratory experiments in which saline solutions and fresh water are used to create density differences. Two characteristic timescales are identified: the filling box time ($T_f$), proportional to the time taken for fluid from a plume to fill a closed box; and the draining box time ($T_d$), proportional to the time taken for a ventilated box to drain of buoyant fluid. The timescale for the flow to reach the steady state depends on these two timescales, which are functions of the box height $H$ and cross-sectional area $S$, the ‘effective’ opening area $A^*$, and the strength, number and distribution of the buoyancy inputs. The steady-state flow is shown to be characterized by the ratio of these timescales ($\mu\,{=}\,T_d/T_f$) which is equivalent to the dimensionless vent area $A^*/H^2$. A feature of these flows is that for $\mu\,{>}\,\mu_c$ the depth of the buoyant upper layer may exceed, or ‘overshoot’, the steady layer depth during the initial transient. The value of $\mu_c$ is determined for both line and point-source plumes, and the sensitivity of the developing flow to the distribution of buoyancy input assessed.