Characterization of the three-dimensional turbulent boundary layer in a concentric annulus with a rotating inner cylinder

Direct numerical simulations of fluid flow through a concentric annulus with a rotating inner wall were performed at $ReDh=8900$⁠. To elucidate the modifications of the near-wall turbulent structure induced by rotation of the inner wall, we compared data obtained at rotation rates of $N=0.0$ and 0.429 for a system with a radius ratio $(R*)$ of 0.5. Conditional quadrant/octant analysis and probability density functions of the velocity fluctuations revealed distinctive features of the three-dimensional turbulent boundary layer (3DTBL) in the concentric annulus with a rotating inner wall. Coherent structures near the inner wall were identified by a $λ2$-based eduction scheme to give the detailed information on the activated near-wall turbulent structures. The ensemble-averaging of the educed coherent vortices showed that enhanced ejections near the vortices were primarily responsible for the augmented turbulent structures. The alteration of the turbulent structures was attributed to the centrifugal force arising from rotation of the inner wall. The assumption of Littell and Eaton on the cause of the altered turbulent structures in 3DTBLs was invalid in the present study. Taken together, the present results showed that the 3DTBL in a rotating concentric annulus has features different from those observed in other types of 3DTBL due to the transverse curvature.