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Abstract The paper presents the results of an investigation of a possibility for energy harvesting from a flexible material such as an ionic polymer–metal composite (IPMC) placed in a steady flow of air characteristic of conditions typical to a densely urbanized area. As electro-active devices require dynamic loading to produce current, their response is usually evaluated in unsteady and turbulent flows, where an electro-active polymer follows the movement of the medium surrounding the device. In our study, we examine the flow conditions at which flutter sets the IPMC strip in motion. Although flutter is often perceived as an unfavorable phenomenon for aerodynamic applications and civil structures, it may be beneficial for harvesting wind energy. Of particular interest is that this phenomenon may occur in a steady flow, which potentially expands the range of favorable flow conditions for energy harvesting. In the paper, the air speed at which flutter occurs and the speed range at which flutter is sustained are provided along with the estimated amount of power produced in an IPMC sample of specified dimensions. 

Falling particle curtains are important in many engineering applications, including receivers for concentrating solar power (CSP) facilities. During the formation of such a curtain, we observe a multiphase analog of Rayleigh-Taylor instability. It was originally described in 2011 for a situation when air sparsely seeded with glycol droplets was placed above a volume of unseeded air, producing an unstably stratified average density distribution that was characterized by an effective Atwood number 0.03. In that case, the evolution of the instability was indistinguishable from single-phase Rayleigh-Taylor instability with the same Atwood number, as the presence of the droplets largely acted as an additional contribution to the mean density of the gaseous medium. Here we present experiments where the volume (and mass) fraction of the seeding particles in gas is considerably higher, and the gravity-driven flow is dominated by the particle movement. In this case, the evolution of the observed instability appears significantly different.