Flow-induced vibration response mapping for non-canonical afterbody geometries

Flow-induced vibration (FIV) prediction for non-canonical bluff bodies remains challenging due to hybrid regimes that differ from the classical vortex-induced vibration (VIV) and galloping. While canonical bluff bodies, such as circular cylinders and square cylinders at high (>20°) angles of attack, exhibit well-defined responses like vortex-induced vibration (VIV), non-canonical bodies can exhibit complex dynamics. For instance, a D-section cylinder with its flat face upstream primarily undergoes VIV at low reduced velocities, transitions to a hybrid VIV-galloping regime at intermediate velocities, and ultimately shifts to galloping at high reduced velocities. In contrast, a square cylinder oriented with its flat face upstream (zero angle of attack; same forebody as the D-section cylinder but with a different afterbody) exhibits classical galloping behavior. To give another example, a reverse D-section cylinder (curved face upstream and no afterbody) exhibits VIV at low mass ratios, whereas a complex response (which can be classified as neither VIV nor galloping) occurs at high mass ratios. In contrast, a circular cylinder (which has a curved forebody and afterbody) exhibits pure VIV across all mass ratios. This demonstrates that the FIV dynamics cannot be determined by the forebody or afterbody geometry in isolation; instead, the combined effects of the two need to be studied to uncover the flow interactions that initiate and sustain the FIVs. Therefore, we systematically vary the afterbody shape (curvature) and size (aspect ratio) for various (smooth and sharp-edged) forebodies in pursuit of developing a predictive FIV model for non-canonical bluff bodies. An overset grid framework with curvilinear grids is applied to handle complex geometries, and the Navier-Stokes equations in a non-inertial reference frame are solved to model body oscillations. The simulation results enable the generation of a comprehensive FIV response map to predict vibration amplitude and frequency for various bluff body geometries.