Experimental optimization of disc-type generators for low-velocity hydrokinetic energy harvesting

The Flow-induced Motion (FIM) of elastically-supported triangular prisms is experimentally investigated, with system comparisons conducted across generators of varying rated powers, to reveal the hydrokinetic energy conversion of disc-type generators. The incoming flow (U = 0.556 m/s-1.209 m/s) covers the Reynolds number range of 48,567 ≤ Re ≤ 105,606 in TrSL3. Variable load resistances R_L (4 Ω ≤ R_L≤31 Ω) are applied to change the total damping in the system, and the optimal damping is determined through power generation experiments. The oscillation responses and energy conversion of the system are analyzed, along with displacement time history and power spectrum of the oscillations. Through experimental studies, the disc-type generator exhibits better power generation performance compared to traditional rotational generators. The results contribute to a more comprehensive understanding on the flow-induced motion and energy conversion of the disc-type generators, and the main findings can be summed as: (1) The best branch for oscillation responses is defined as the galloping branch at a larger load resistance, the maximum amplitude ratio A^*=1.72 is observed at R_L=21 Ω with the generator rated at 300 W. (2) The energy conversion of the system varied with different generators, suggesting that there exists optimal damping for the generators. (3) The generator rated at 200 W has the best performance on energy harvesting in the tests. The maximum active power is P_max=21.09 W at R_L=11 Ω and U_r=8.1, corresponding to the efficiency of η_harn = 9.15%. The maximum energy conversion efficiency is 12.13% at R_L=11 Ω and U_r=5.2, corresponding to the active power of P_harn=3.94 W.