Effect of Confinement on Flow Around a Rotating Elliptic Cylinder in Laminar Flow Regime

The flow phenomena around a rotating elliptic cylinder placed in a narrow channel is studied numerically. The walls of the channel act as a confinement that limits the flow in the transverse direction. The confinement ratio $(β)$⁠, nondimensional rotation rate $(α)$⁠, and the Reynolds number (Re) span across multiple values. A parametric study is done to identify the variations in drag-coefficient $(CD)$⁠, lift-coefficient $(CL)$⁠, and moment coefficient $(CM)$ with changes in $β, α$⁠, and Re. Near-field and far-field vorticity contours are discussed in detail. fast Fourier transform (FFT) of the time-periodic lift signals are presented to understand the shedding-frequency characteristics. Furthermore, $CM$ values are analyzed for possible cases of autorotation. It is observed that confinement acts to delay the shedding of vortices. However, a complete suppression is not obtained even for the maximum value of $β$⁠. This is likely because of the sharp flow separation at the edges of the cylinder, which tends to promote the formation of a vortex. Hovering vortices are observed for $α>1$⁠, and a special case is identified for which the hovering vortex never dissipates.