Heng Deng

The advantageous performance in terms of energy conversion for the flow-induced motion (FIM) of T-section prisms has been experimentally reported recently. In order to further understand the oscillation and energy conversion of multiple T-section prisms, a series of tests of two T-section prisms arranged in tandem with five different spacing ratios (3 ≤ L/D ≤ 15) and seven load resistances (8 Ω ≤ R_L ≤ 41 Ω) were conducted. The effects of the spacing ratio and load resistances on energy conversion were discussed. The main conclusions can be summarized as follows. For most tests, the amplitudes of the upstream T-section prism (UTP) and downstream T-section prism (DTP) were both lower than the amplitude of the single T-section prism (STP) due to the mutual interference of the two prisms. Because of the mutual interference, the active powers of UTP and DTP were both less than that of STP, but at some special spacing ratios or load resistances, the mutual interference benefited the energy converted by the two prisms. In the presented tests, the total optimal active power of the upstream T-section prism and downstream T-section prism (UTP + DTP) was 30.12 W, which was 1.5 times that of STP (20.12 W).

Flow-induced motion (FIM) performs well in energy conversion but has been barely investigated, particularly for prisms with sharp sections. Previous studies have proven that T-section prisms that undergo galloping branches with high amplitude are beneficial to energy conversions. The FIM experimental setup designed by Tianjin University (TJU) was improved to conduct a series of FIM responses and energy conversion tests on a T-section prism. Experimental results are presented and discussed, to reveal the complete FIM responses and power generation characteristics of the T-section prism under different load resistances and section aspect ratios. The main findings are summarized as follows. (1) Hard galloping (HG), soft galloping (SG), and critical galloping (CG) can be observed by varying load resistances. When the load resistances are low, HG occurs; otherwise, SG occurs. (2) In the galloping branch, the highest amplitude and the most stable oscillation cause high-quality electrical energy production by the generator. Therefore, the galloping branch is the best branch for harvesting energy. (3) In the galloping branch, as the load resistances decrease, the active power continually increases until the prism is suppressed from galloping to a vortex-induced vibration (VIV) lower branch with a maximum active power P_harn of 21.23 W and a maximum η_out of 20.2%. (4) Different section aspect ratios (α) can significantly influence the FIM responses and energy conversions of the T-section prism. For small aspect ratios, galloping is hardly observed in the complete responses, but the power generation efficiency (η_out,0.8 = 27.44%) becomes larger in the galloping branch.