Hydrokinetic energy harnessing by spring-mounted oscillators in FIM with different cross sections: From triangle to circle

Flow-Induced Motion (FIM) phenomena of spring-mounted oscillators were numerically investigated with 2-dimensional simulations to examine the effects of cross section on hydrokinetic energy harnessing. In the simulations, the test flow speed increases from 0.2 m/s to 3.0 m/s (1.61×10⁴ <Re (Reynolds number) < 2.42×10⁵). Six selective cross sections (i.e. triangle, square, hexagon, octagon, 24-sided polygon, and circle) are applied in this study. Results suggest that in the Vortex-Induced Vibration (VIV) region, the response of circular cylinder is the strongest; the maximum amplitude (0.078 m) and maximum converted power (4.6W) are achieved at Re = 4.6×10⁴. Meanwhile, the maximum energy conversion efficiency (34.5%) is also obtained in the VIV region. In the galloping region, decreasing the number of sides of cross section will enhance the FIM responses. More specifically, the amplitude and converted power of the triangular prism are the highest. However, the energy conversion efficiency in the galloping region is significantly lower than that in the VIV region, although the maximum converted power is always obtained at the highest flow speed in the galloping region. Besides, for the smooth circular cylinder, when Re > 9.6 × 10⁴, the amplitude approaches zero, which means the frequency lock-in phenomenon disappears and the response no longer belongs to VIV or galloping.