Design and CFD Simulations of a Vortex-Induced Piezoelectric Energy Converter (VIPEC) for Underwater Environment

Abstract

Abstract:A novel vortex-induced piezoelectric energy converter (VIPEC) is presented in this paper to harvest ocean kinetic energy in the underwater environment. The converter consists of a circular cylinder, a pivoted plate attached to the tail of the cylinder, several piezoelectric patches and a storage circuit. Vortex-induced pressure difference acts on the plate and drives the plate to squeeze piezo patches to convert fluid dynamic energy into electric energy. The output voltage is derived from the piezoelectric constitutive equation with fluid forces. In order to evaluate the performance of the VIPEC, two-dimensional computational fluid dynamics (CFD) simulations based on the Reynolds averaged Navier-Stokes (RANS) equation and the shear stress transport (SST) k-ω turbulence model are conducted. The CFD method is firstly verified for different grid resolutions and time steps, and then validated using simulation and experimental data. The influences of the plate length and flow velocity on the wake structure, the driving force and the performance of the VIPEC are investigated. The results reveal that different parameters reach their peaks at different plate lengths, and the converter has a maximal output voltage of 2.3 mV in a specified condition and the maximal power density reaches 0.035 µW/m 3 with a resistance load of 10 MΩ. The influence of the simulated subcritical Reynolds number on the driving force is not noticeable. The simulation results also demonstrate the feasibility of this device.

Layout Optimization Design of Two Vortex Induced Piezoelectric Energy Converters (VIPECs) Using the Combined Kriging Surrogate Model and Particle Swarm Optimization Method

“…Due to the narrow gap between the cylinder and the internal revolute joint inside it, the plate was solely stuck with piezo patches rather than the cylinder. As a result, the plate's vibration amplitude was bounded and it was possible to approximate the output voltage with a stationary VIPEC with high precision through a two-dimensional simulation, as explained in previous work [15]. Hence, stationary wall conditions were implemented on all sides of the VIPEC including the cylinder and the plate, i.e., both the zero normal and tangential velocity conditions were imposed on those walls.…”

“…Periodical vortex shedding occurred at the back of the cylinder and detached from either side of it due to the flow separation around the cylinder. Studies on a single VIPEC including its governing equations, boundary conditions, the influence of geometric parameters on its hydrodynamic, and voltage performance have been elaborated in previous work [15]. Therefore, this paper puts emphasis on the interaction of two VIPECs and tries to determine their optimal layout parameter.…”

“…Hence, stationary wall conditions were implemented on all sides of the VIPEC including the cylinder and the plate, i.e., both the zero normal and tangential velocity conditions were imposed on those walls. The output voltage was predicted at the plate's average position like a single VIPEC to evaluate its performance [15].…”

“…In order to maximize the output voltage of two VIPECs, the layout configuration design was based on an optimal VIPEC from previous work, that is, the cylinder's diameter (D) was 35 mm and the plate's dimensionless length was L * = L D = 2.5, where L is the plate's length [15]. The open circuit output voltage was derived through the piezoelectric constitutive equation and is expressed as [15,16]:…”

“…In order to establish the output voltage's response surface model, it is necessary to obtain a number of simulation results in advance. Computational Fluid Dynamics (CFD) simulations can predict the hydrodynamic performance of the VIPEC and its output voltage with high accuracy [15]. CFD simulations are conducted at prescribed sampled points to obtain necessary information on these points.…”