Hydrodynamic Force of an Obliquely Oscillating Cylinder in Steady Flow

This study conducts a series of three-dimensional numerical simulations to explore the dynamics of an oscillating cylinder in steady current. Simulations are set at a fixed Reynolds number of 500 for the steady current and a small oscillation amplitude of 0.4 cylinder diameter. Seven oscillation angles θ from 0° to 90°, defining as the orientation of the cylinder oscillation relative to the current, have been investigated across various oscillation wavelengths λ*. The impact of θ on the wake characteristics can be broadly categorized into three regions. For small λ* (less than 1.5), the flow is predominantly influenced by the cylinder oscillation, with forces that vary monotonically with respect to θ. In contrast, at larger λ* (greater than 10), cylinder oscillation becomes negligible, and the wake is primarily driven by the incoming flow. Complex wake interactions exist at intermediate λ* = 1.5–10, particularly in terms of the occurrence of lock-on states. The primary lock-on at θ = 90° (period-1 wake), characterized by a repeatable vortex shedding pattern over each oscillation period, develops at all angles. Meanwhile, the primarily lock-on state at θ = 0° (period-2 wake) is only observed for θ up to about 75°. As θ increases from 0°, both lock-on states shift towards smaller λ*.