Rayleigh–Taylor instability in complex stratifications
Rayleigh–Taylor instability in complex stratifications
复制标题
复杂分层中的瑞利-泰勒不稳定性
DOI：
--
复制
发表时间：
2005
影响因子：
3.7
通讯作者：
S. Dalziel
中科院分区：
文献类型：
--
作者：
J. Jacobs;S. Dalziel
实验研究了由一个不稳定界面和一个稳定界面分隔的三流体系统的瑞利-泰勒不稳定性。实验是重力驱动的，并进行了由盐溶液和淡水组成的可混溶液体。下面的两层最初是重力稳定的，是通过将较轻的流体沉积在较重的流体的较厚层的顶部而形成的。相对较厚的顶层最初通过在实验开始时移除的刚性屏障与两个较低的层分离。在底层流体的密度等于顶层流体的密度的情况下，所得到的湍流被发现是自相似的，所示的平均浓度分布的崩溃，以及平均浓度曲线的峰值的衰减的行为。在这种配置中，底层的上部不稳定界面所产生的湍流的侵蚀被发现是小的。当底层流体的密度增加到高于顶层流体的密度时，侵蚀程度进一步减小。在较低的界面是稳定分层的情况下，在较低的（静态稳定）界面的夹带率E被发现遵循幂律的理查森数，即$E propto Ri^{-n}$，与$n {approx} 1.3$，结果与研究的振荡网格诱导的混合。当底层流体的密度降低到顶层流体的密度以下时，侵蚀如预期的那样增加。然而，在这种情况下，整体密度分布是这样的，它是全局瑞利-泰勒不稳定的在后期的时间。在这种情况下，湍流混合区在后期的增长类似于单界面Rayleigh-Taylor不稳定性，具有近似相同的增长常数值。在这些后期不稳定的实验中，密度分布接近一个等效的两层瑞利-泰勒不稳定系统。
The Rayleigh–Taylor instability of a system of three fluids separated by one unstable and one stable interface has been investigated experimentally. The experiments were gravitationally driven and conducted with miscible liquids consisting of salt solutions and fresh water. The lower two layers are initially gravitationally stable and are formed by depositing the lighter fluid on top of a thicker layer of the heavier one. The relatively thick top layer is initially separated from the two lower layers by a rigid barrier that is removed at the start of an experiment. In situations where the density of the bottom-layer fluid equals that of the top-layer fluid, the resulting turbulent flow is found to be self-similar as demonstrated by the collapse of the mean concentration distributions as well as the behaviour of the decay of the peak of the mean concentration profiles. In this configuration, the erosion of the bottom layer by the turbulence generated by the upper unstable interface is found to be small. When the density of the bottom-layer fluid is increased above that of the top-layer fluid, the degree of erosion is further decreased. In the cases where the lower interface is stably stratified at late-time, the entrainment rate E at the lower (statically stable) interface is found to follow a power law of the Richardson number, i.e. $E propto Ri^{-n}$, with $n {approx} 1.3$, a result in agreement with studies of mixing induced by oscillating grids. When the density of the bottom-layer fluid is decreased below that of the top-layer fluid, the erosion increases as expected. However, in this case, the overall density distribution is such that it is globally Rayleigh–Taylor unstable at late time. In this situation, the turbulent mixing region at late times grows similarly to that of single-interface Rayleigh–Taylor instability with approximately the same value of the growth constant. In these late-time unstable experiments the density profile approaches that of an equivalent two-layer Rayleigh–Taylor unstable system.