Rotation-driven suppression and re-emergence of unsteady flow past a circular cylinder

The flow past a rotating cylinder undergoes substantial changes in its wake dynamics and aerodynamic response with increasing rotation rate. This study investigates these changes in two-dimensional compressible flow at \(Re_\infty=3800\) and \(M_\infty=0.1\), with the rotation rate systematically varied over \(0.1\leqΩ\leq10\) using 130 high-fidelity simulations. At low rotation rates, conventional periodic vortex shedding is progressively suppressed with increasing rotation. A narrow transition regime around \(Ω=2.2-2.8\) is identified, where sustained oscillations evolve into intermittent fluctuations before reaching a nearly quiescent state. At higher rotation rates, unsteadiness re-emerges with distinctly intermittent and multiscale characteristics, demonstrating that this instability is fundamentally different from conventional Kármán shedding. The surface pressure and streamwise skin-friction distributions reveal substantial redistribution of aerodynamic loading with rotation, characterized by increasingly intense suction and significant modification of the near-wall shear field. The maximum lift increases systematically with rotation, reflecting the strengthening Magnus-Robins effect, whereas drag exhibits a non-monotonic response with enhanced variability at high rotation rates. Despite the low free-stream Mach number, rotational acceleration produces local Mach numbers approaching 0.5, indicating appreciable compressibility effects in the near-cylinder region. Vorticity-based proper orthogonal decomposition further reveals a transition from wake-dominated coherent structures at low rotation to strongly wrapped, rotation-dominated structures at high rotation. These results establish a direct connection between rotational forcing, surface loading, compressibility, and the suppression and subsequent re-emergence of flow unsteadiness.