Ni-Cr single splats were plasma-sprayed at room temperature onto aluminum and stainless steel substrates, which were modified by thermal and hydrothermal treatments to control the oxide surface chemistry. The proportions of the different splat types were found to vary as a function of substrate pretreatment, especially when the pretreatment involved heating. It was observed that surface roughness did not correlate with changes in splat morphology. Substrate surfaces were characterized by X-ray photoelectron spectroscopy using in situ heating in vacuum to determine the effect of thermal pretreatment on substrate surface chemistry. It was found that the surface layers were composed primarily of oxyhydroxides. When the substrates were heated to 350°C, water vapor was released from the dehydration of oxyhydroxide. Preheating the substrate can remove the water prior to spraying: preheated substrates had improved the physical contact between the splat and substrate, which enhanced the formation of disk splats and increased the number of splats.

This study proposes a novel wind energy harvester that exploits both vortex-induced vibration (VIV) and galloping phenomena with a hybrid cross-sectioned bluff body. Magnetic-induced monostable nonlinearity is then introduced in the harvester to improve its energy harvesting performance. The bluff-body cross section uses the combination of 3/4 round and 1/4 square to introduce the coupled VIV and galloping, and the magnetic repulsive force of the two magnets is employed to realize the monostable nonlinearity. Governing equations bringing together the VIV, galloping and magnet-induced monostable nonlinearity are established. Wind tunnel experiment is first conducted to validate the aerodynamic model of the governing equations without the monostable nonlinearity, which reveals the advantage of the coupled VIV and galloping for performance improvement. Consequently, the numerical simulations are performed to reveal the benefit of the magnet-induced monostable nonlinearity for wind energy harvesting. Results show that compared to the coupled VIV-galloping harvester without the monostable nonlinearity, the proposed monostable harvester can reduce the cut-in speed of galloping, which boosts the voltage output in a wider wind speed range and further promotes the advantages of the combination of VIV and galloping.

No abstract

No abstract

No abstract