## 1 Introduction
The previous researchers showed that non-circular bluff bodies were more prone to galloping, and the passive turbulence control (PTC) cylinder (32), triangular prism (33; 34), rectangular cylinder (35), and T-section prism (36) were experimentally proved to have better energy conversion capacity, and the harnessed power in water was much higher than that in air. [PERSON] et al. (2019, 2021) proposed an optimized experimental design method for a piezoelectric energy generator which effectively collected kinetic energy from FIM and provided  
Figure 2: The amplitude response of a downstream cylinder to a circular cylinder: (**a**) Response of the downstream cylinder for typical VIV and WIV responses; (**b**) Response of the downstream cylinder at different spacing Reproduced with permission from (24), Copyright Cambridge University Press, 2010.  
sustainable power for microelectronic products. Various cross-sections of the interference cylinder were proposed; with a wind speed of 2.36 m/s and _L_/_D_ = 0.9, the average output power of a square prism was 803.4 uW. [PERSON] et al. [39] produced a novel wind energy harvester named a vibro-impact dielectric elastomer generator (VI DEG) which can harness power up to 0.16 mW by increasing the stiffness of the system and adjusting the distance between the DEMs appropriately. [PERSON] [40] carried out a series of experiments of two smooth cylinders and two PTC cylinders to compare the oscillation responses. The results showed that the amplitude of the downstream PTC was close to that of the upstream PTC and single PTC for \(U^{*}_{water}=U\)/\(f_{water}\)_D_) \(\geq\) 8. Based on the experiments, [PERSON] et al. [41] and [PERSON] et al. [42] conducted a series of comprehensive tests on the free vibration of multi-PTC cylinders and concluded the optimal arrangement of PTC cylinders. [PERSON] et al. [43] also performed numerical simulation of the energy conversion of tandem PTC cylinders. The peak energy conversion efficiency reached 37%, which was close to the efficiency of experiments. [PERSON] et al. [44,45] proposed a two-dimensional numerical simulation method to study the vortex-induced vibration energy conversion with a spacing ratio of 2 \(\leq\)_L_/_D_ \(\leq\) 50, and the cir-tria section (\(\eta\) = 26.5 %) was the best of five cross sections. Meanwhile, the energy conversion of rectangue with different aspect ratios has been discussed and analyzed. [46] The influence of the submergence depths of cylinders had been examined to explore more thoroughly the VIV responses based on simulation and experimental results. As the submergence depth decreases, the VIV amplitude decreases, with a similar decrease in the hydrokinetic energy conversion [47]. [PERSON] et al. [48] creatively proposed a new converter consisting of an elastically mounted circular cylinder and a free-to-rate pentagram impeller to harness hydrokinetic energy. The average energy conversion efficiency is about 22.6%, and the power density can reach 885.53 W/m\({}^{3}\), which can be achieved by two-way fluid-structure interaction simulations. FIM responses and energy conversion tests of T-section prisms have been conducted at Tianjin University with the maximum active power of 21.23 W [36], which was slightly lower than that of the PTC cylinder (23.54 W) reported by [PERSON] [49]. The hard galloping (HG) and soft galloping (SG) investigated experimentally for triangular prisms [33] can also be observed for T-section prisms. There are still many issues that remain to be addressed. For example, the oscillation responses of UTP and DTP are not clear, especially for variation of spacing and load resistances. The experimental study has two objectives. The first one is to determine the mutual interference responses of the upstream T-section prism (UTP) and downstream T-section prism (DTP). The second aim is to estimate the energy conversion of UTP and DTP, as well as the influence of the spacing ratio and load resistances on energy conversion.