Biomimetic Groove and Elliptical Bluffness Synergy for Enhanced Vortex-Induced Vibration Excitation

This study investigates the passive amplification of aerodynamic excitation forces through coordinated bluff-body geometric modifications to quantify the vortex-induced vibration (VIV) energy harvesting potential of stationary cylinders in the laminar regime. Two-dimensional laminar simulations on fixed bodies isolate geometric effects from structural feedback. Circumferential biomimetic grooves are first optimised on a circular baseline at $\mathrm{R}\mathrm{e}=200$ using a Taguchi orthogonal array (L9), identifying groove amplitude as the dominant control parameter and selecting $N=24$, $Amp=5\mathrm{\%}$ as the optimal configuration, which yields a $21\mathrm{\%}$ increase in the root-mean-square lift coefficient ( $C_{\ell ,\mathrm{r}\mathrm{m}\mathrm{s}}$) and a $12.5\mathrm{\%}$ Strouhal number reduction relative to the smooth circular baseline. The optimal groove profile is coupled with vertically-oriented bluff elliptical bases at three aspect ratios ( $AR=1.0$, $0.75$, and $0.50$). Proper Orthogonal Decomposition (POD), wake fluctuation energy (WFE) mapping, and a simplified one-degree-of-freedom (1-DOF) structural projection model quantify the aerodynamic excitation power across all six configurations. Results reveal a geometric sweet spot at $AR=0.75$, where the Grooved configuration achieves the highest projected aerodynamic excitation power ( $P_{\text{est}}=0.5184$ W/m), corresponding to a 2.24-fold amplification of the available fixed-body forcing relative to the smooth circular baseline and outperforming the aggressively bluff Grooved $AR=0.50$ geometry. This counter-intuitive result is attributed to groove-to-boundary-layer interaction saturation: at $AR=0.50$, the shortened streamwise body dimension suppresses the shear-layer tripping mechanism. POD analysis confirms high modal coherence at the optimum, with the first two modes capturing $96.2\mathrm{\%}$ of the total fluctuation energy, indicating forcing characteristics favourable for sustained VIV lock-in. A complementary Reynolds-number sensitivity analysis conducted at $\mathrm{R}\mathrm{e}=100$ and $150$ further reveals that the groove contribution at $AR=0.50$ remains uniformly suppressed relative to $AR=0.75$ across the full laminar range, confirming that the saturation mechanism is a robust geometric feature rather than a Reynolds-specific artefact. However, the absolute geometric optimum is Reynolds-number dependent. $AR=0.50$ delivers stronger excitation at $\mathrm{R}\mathrm{e}=100$, the two configurations converge at $\mathrm{R}\mathrm{e}=150$, and $AR=0.75$ is the best-performing aspect ratio among those evaluated at $\mathrm{R}\mathrm{e}=200$, indicating the onset of the boundary-layer saturation mechanism at $\mathrm{R}\mathrm{e}=150$.