Inertial wave mode excitation in a rotating annulus with partially librating boundaries
Inertial wave mode excitation in a rotating annulus with partially librating boundaries
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DOI：
10.1088/0169-5983/46/4/041423
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发表时间：
2014-07
影响因子：
1.5
通讯作者：
I. Borcia;Ghasemi V Abouzar;U. Harlander
中科院分区：
文献类型：
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作者：
I. Borcia;Ghasemi V Abouzar;U. Harlander
通过调节外筒和上、下盖的转速，在充满流体的旋转环空中激发惯性模式。由于边界层中的周期性运动，这种强迫导致惯性波束从环带的拐角区域发射出来。当强迫频率与旋转环的本征频率匹配时，波束方向图幅度增大，波束展宽，可以观察到模式结构。将本征模与相应的无粘问题的解析解进行了比较。特别是对于压力场，可以找到一个很好的一致性。然而，在所有频率下，都存在与激励波束相关的剪切层。这一点在使用Kalliroscope粒子进行的实验可视化中变得尤为明显，突出了流体中的相对运动。比较本征频率，我们发现相对于解析频率，实验频率和数值频率显示出向更高频率的微小移动。这种频移是由于在振动外壁存在斯托克斯边界层而导致的有效共振体积的减小。由于作用力的对称性，并不是所有可能的模都能被激发。结果表明，只有相对于旋转轴的对称模存在。从根本上讲，这项研究可能有助于更好地理解振动行星和卫星中的惯性模式激发，在这些行星和卫星中，惯性波从内部或外部球面边界的临界点发射。
Inertial modes are excited in a fluid filled rotating annulus by modulating the rotation rate of the outer cylinder and the upper and lower lids. This forcing leads to inertial wave beams being emitted from the corner regions of the annulus due to periodic motions in the boundary layers. When the forcing frequency matches the eigenfrequency of the rotating annulus the beam pattern amplitude is increasing, the beams broaden and mode structures can be observed. The eigenmodes are compared with analytical solutions of the corresponding inviscid problem. In particular for the pressure field a good agreement can be found. However, shear layers related to the excited wave beams are present for all frequencies. This becomes obvious particularly in the experimental visualizations that are carried out by using Kalliroscope particles, highlighting relative motion in the fluid. Comparing the eigenfrequencies we find that relative to the analytical frequencies, the experimental and numerical ones show a small shift towards higher frequencies. This frequency shift is due to the reduction of the effective resonance volume that results from the existence of a Stokes boundary layer at the outer librating wall. Due to the symmetry of the forcing not all possible modes can be excited. It is shown that only symmetric modes with respect to the rotation axis exist. From a fundamental perspective, the study might help to better understand inertial mode excitation in librating planets and moons where inertial waves are emitted from critical points on the inner or outer spherical boundary.