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Direct numerical simulations (DNSs) of rotating turbulent Poiseuille flows are performed to study the effects of system rotation on the kinematics of the quasi-streamwise vortices. By using the second invariant of the deformation tensor, a number of streamwise vortices are detected and averaged in the wall vicinity. As observed in the homogeneous shear flow(1), with the increase in the system rotation the streamwise vortical structures tend to be aligned and elongated in the streamwise direction, and their shape in the cross streamwise plane becomes more circular rather than elliptic. In the case of smaller angular frequency, the streamwise vortices tend to be accompanied by the vortices of opposite streamwise vorticity in both ejection and sweep sides of the vortex, where inrush motion of fluids toward the wall, and outward motion from the wall are observed, respectively. With increase in the system rotation, vortices in the sweep side are attenuated, though those in the ejection side are enhanced. Enhancement of vortices in the ejection side is found to be attributed to the alignment of vortical structure and low- speed streak in the streamwise direction.
Author(s):
Oaki Iida
Japan