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Abstract
The structure and dynamics of coherent vortex tubes in the zero-absolute-vorticity state (ZAVS), which is realized in a rotating uniformly sheared flow with zero mean absolute vorticity, are investigated by the use of the results of direct numerical simulations. A coherent vortex tube consists of two parts; two end parts and an intermediate part between them. The end parts keep the inclination angle against the tilting mechanism by the mean shear flow and rotate the vortex tubes from the direction of the mean-shear vorticity at their birth period to that of the system rotation as time proceeds. The generation of the Reynolds stress is activated in the regions near the end parts. The change in the direction of the vortex tubes toward that of the system rotation contributes to the stabilization of the whole turbulent flow field. The vortex tubes are deformed and flattened as they are turned toward the direction of the system rotation, which leads to the decay of the vortex tubes. The deformation of the vortex tubes also causes the decrease in the Reynolds stress, which suppresses the growth of the turbulence kinetic energy. The interaction between coherent vortex tubes are also investigated in various configurations.