The VIVACE Converter: Model Tests at High Damping and Reynolds Number Around 10⁵

The VIVACE Converter is a new concept to generate clean and renewable energy from fluid flows such as those abundant in oceans, rivers or other water resources. The underlying concepts for design, scaling, and operation of VIVACE (Vortex Induced Vibrations Aquatic Clean Energy) were introduced in our previous paper. In its simplest form, a VIVACE modulo consists of a single rigid cylinder mounted on elastic supports and connected to a Power Take Off (PTO) system. The cylinder is placed in a steady unidirectional current and excited in VIV. In this paper, the VIVACE modulo was tested in the Low Turbulence Free Surface Water Channel of the University of Michigan to demonstrate the concept, generate electricity, measure its efficiency, and calculate basic benchmarking measures such as energy density. Tests performed were tailored to the particulars of the VIVACE modulo which dictate that the cylinder operate in VIV under high damping and as high a Reynolds number as possible. At the same time, a broad range of synchronization is required to make VIVACE effective in energy generation in a realistic environment. Due to these requirements, VIV tests have not been performed before in the subspace applicable to the operation of the VIVACE modulo. In the process of extracting fluid kinetic energy and converting it to electricity in the lab, for a given set of cylinder-springs-transmission-generator, only the damping used for harnessing electricity was optimized. Even at this early stage of development, for the tested VIVACE modulo, the maximum peak efficiency achieved was η_Peak = 0.308; the corresponding integrated power efficiency in that particular test was η_VIVACE = 0.22 with theoretical upper limit based on measurements of η_UL-VIVACE = 0.3663. Such a high efficiency was achieved even at the low velocity U = 0.840m/sec = 1.63knots.