Numerical Investigation of the Afterbody Effects on Flow-Induced Vibration

Modeling and prediction of flow-induced vibration (FIV) of non-canonical bluff bodies is challenging because their responses can depart from classical vortex-induced vibration (VIV) and galloping. While canonical configurations such as circular cylinders and square cylinders at zero angle of attack exhibit well-defined VIV and galloping responses, respectively, structures with modified forebody–afterbody combinations can show hybrid or transitional behavior. In this study, we isolate the role of afterbody by considering a two-dimensional bluff body with a fixed circular forebody and a super-ellipsoidal afterbody of varying curvature �� and a fixed aspect ratio. The flow equations are solved in a non-inertial frame attached to the oscillating cylinder, coupled to a single degree-of-freedom spring–mass–damper system, using a high-order in-house solver on an overset curvilinear grid. The simulations show that low-curvature afterbodies (�� ≈ 1.0 − 1.5) produce a galloping response, high-curvature afterbodies (�� ≳ 1.7) exhibit the classical VIV, and an intermediate curvature (�� ≈ 1.6) yields a mixed VIV–galloping regime. Analysis of vorticity fields, wake modes, energy-transfer metrics, and separation angles confirms that these behaviors arise from how the afterbody curvature controls shear-layer separation/reattachment, vortex wrapping around the trailing edge, and cross-wake interaction. The results demonstrate that modest changes in afterbody curvature are sufficient to switch, or blend, the dominant FIV mechanism for a given circular forebody.