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首页> 外文会议>International Conference on Computational Methods and Experimental Measurements(CMEM/07); 2007; Prague(CZ) >Stability of stratified spin-up flows
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Stability of stratified spin-up flows

机译：分层旋转流的稳定性

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摘要

The stability of stratified rotating flows is investigated by means of laboratory experiments in axisymmetric cylindrical and annular containers with both horizontal and sloping bottoms. The baroclinic current is initiated via incremental spin-up/down of a linearly stratified fluid by an abrupt change in the rotation rate of the system (from Ω ± ΔΩ to Ω). The flow stability depends on the characteristic values of the Rossby number, ε = ΔΩ/Ω, and the Burger number, B_u = NH/fR, where f = 2Ω is the Coriolis parameter, R is the characteristic horizontal length scale of the flow, H is the depth of the fluid layer, and N is the buoyancy frequency. Particular attention is given to the nonlinear flow regime (finite Rossby numbers). It is found that axisymmetric spin-up current loses its azimuthal symmetry when B_u < 1, and breaks into a system of large-scale cyclonic and anticyclonic vortices with a predominantly vertical axis of rotation. The eddies always develop at the density fronts formed by the corner regions adjacent to the sidewalls of the container. The corner regions reach a quasi-equilibrium state at the characteristic time scale E~(-1/2)Ω_(-1) (where E = v/ΩH~2 is the Ekman number and v is the kinematic viscosity), which is also observed for homogenous fluids. It is also shown that the stability of the spin-up flow is affected by the bottom slope. In the presence of the latter the bottom boundary layer experiences a qualitatively different behavior. While the density field demonstrates a smooth monotonic behavior in the case of stratified spin-up at all times, it reveals high-frequency fluctuations in the spin-down case, suggesting the turbulent nature of the bottom boundary layer. The results of observations may be found useful in interpreting in-situ measurements of upwelling- and downwelling-favorable oceanic currents in the littoral zones.
机译：通过在水平和倾斜底部均轴对称的圆柱形和环形容器中进行实验室实验，研究了分层旋转流的稳定性。斜压电流是通过系统旋转速度的突然变化（从Ω±ΔΩ到Ω），通过线性分层流体的增量旋转/下降来启动的。流动稳定性取决于Rossby数的特征值ε=ΔΩ/Ω和Burger数B_u = NH / fR，其中f =2Ω是科里奥利参数，R是流动的特征水平长度尺度， H是流体层的深度，N是浮力频率。特别注意非线性流动状态（有限的Rossby数）。发现当B_u <1时，轴对称自旋电流失去其方位对称性，并分解为一个以旋转轴为主的大型旋风和反旋风涡旋系统。涡流总是在与容器侧壁相邻的拐角区域形成的密度前沿形成。拐角区域在特征时间尺度E〜（-1/2）Ω_（-1）处达到准平衡状态（其中E = v /ΩH〜2是埃克曼数，v是运动粘度），即还观察到均匀流体。还显示出旋转速度的稳定性受底部斜率的影响。在后者的存在下，底部边界层经历了质的不同行为。尽管密度场在任何时候都分层旋转时显示出平滑的单调行为，但它在旋转时显示出高频波动，表明底部边界层的湍流性质。观测结果可能有助于解释沿岸带上涌和下涌有利洋流的原位测量。

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