Steady flows in a channel with wavy walls at the periodic pumping of the fluid are experimentally investigated. The channel is formed by two plates with sinusoidal relief located symmetrically relative to each other. The fluid oscillation results in excitation of steady flow in the channel cells. The transformation of the structure of steady flow with the dimensionless frequency of oscillation is systematically studied. In the limit of low dimensionless frequencies, when the oscillating flow in the entire volume of the channel is viscous, the steady flow in each channel cell has the form of a symmetric system of four transverse rolls. With an increase in the dimensionless frequency, the thickness of viscous boundary layers near the channel walls gradually decreases and the primary steady flow induces a secondary flow of the opposite rotation outside the boundary layers. With a further increase in the dimensionless frequency, the secondary flow fills the entire volume of the channel cells. It is found that the intensity of steady flow, which is determined by the pulsational Reynolds number, varies nonmonotonically with the dimensionless frequency. The transformation of the structure and intensity of steady flow with the dimensionless frequency in a wide range of frequency variation is determined. The general dependency of the steady flow intensity on dimensionless frequency is determined. It is found that in the limit of low frequencies, the velocity is mainly determined by the wall relief and poorly depends on the distance between the wavy walls of the channel.
Fluid flow excited by a core oscillating in a rotating spherical cavity is experimentally investigated. Oscillations are set by an external inertial field so that in the reference frame of the cavity, the core moves along a circular trajectory around the rotation axis. Two situations are considered: when the core oscillations are co-directed or counter-directed with respect to the rotation of the cavity. The oscillating core is a source of non-axisymmetric inertial waves that form a system of cone-shaped shear layers in fluid bulk. Depending on the oscillation frequency, various inertial flow regimes arise, the spatial structure of which strongly depends on the sign of the oscillations. It is found that a strong non-linear response in the form of a steady zonal flow corresponds to each flow regime. The flow structure is a system of nested liquid geostrophic cylinders, one of which is associated with the critical latitude at the core boundary, where inertial waves are generated. The next one is associated with the wave reflection from the cavity boundary and is clearly manifested when they are focused on the wave attractor. The most intense zonal flow occurs when inertial waves are superposed and global vortex structures are resonantly excited.
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