Numerical Simulation of Wave Energy Converter With Hydrofoil Blades Under Various Wave Conditions

Abstract

Ocean wave is a rich source of renewable energy with much higher power density than winds. Various WEC technologies have been proposed or are under development. In this study, we developed a 2-dimensional (2D) model and analyzed the rotational motion of the lift-type rotor’s blade under steady flow and unsteady flow. The numerical model was validated by experiments under steady flow. Fast Fourier Transform (FFT) analysis was performed to identify the major contribution of frequency in terms of vortexes generated in the flow field. A comparative study was also performed by comparing all the cases in terms of energy conversion efficiency under different wave conditions. It turns out that the efficiency of energy conversion has a maximum value in the steady flow, while the efficiency for unsteady flow keeps decreasing, therefore this is highly due to the increased dissipation because of the oscillating. When the flow is oscillating, the rotational speed of the rotor under periodic condition is lower than the rotational velocity with steady flow, and a curve fitting was performed in this study to predict the periodic average rotational speed. We conclude that for oscillating flow a minimum of 1.6% energy conversion efficiency can be expected, but it may vary for the actual ocean waves. It is expected the current 2D simulation results can contribute to the wave energy community, especially when the rotor design and optimization is required.

Rotors for wave energy conversion—Practice and possibilities

“…The authors used the waveDyM-Foam solver which is a combination of pimpleDyMFoam (a solver for unsteady multi-phase flow with dynamic mesh treat-FIGURE 20 Rotor power of a horizontal Savonius-type cyclorotor, for different rotor entry angles at varying rotor speed, when submergence depth is equal to the rotors' diameter at mean sea state. [26] FIGURE 21 Efficiency of a vertical Darrieus-type cyclorotor, in oscillating flow, as studied in [10] ment) and waves2Foam (a wave generation function and boundary treatment library).…”

“…The effort to derive a numerical model usually falters due to the computational difficulties of solving a high fidelity model [10,12,[26][27][28]. Almost all relevant cyclorotor mathematical models were developed only for potential flow, monochromatic waves, and generally in a 2D environment.…”

“…Other designs for vertical rotor based WECs follow a simplifies philosophy that avoids the reliance on any information or intervention from weather forecasting, sensing, electrical and or mechanical control. For example, a number of FIGURE 13 Vertical-axis unidirectional cyclorotors for wave energy conversion patented by Yang [25] vertical-axis rotor concepts were presented in the articles of Yang et al [10,25,[45][46][47][48]. These rotors have a number of cup blades or curve hydrofoils, as shown in Figure 13.…”

“…For example, a number of vertical‐axis rotor concepts were presented in the articles of Yang et al. [10, 25, 45–48]. These rotors have a number of cup blades or curve hydrofoils, as shown in Figure 13.…”

“…They are, in general, based on approximate calculations, with some authors obtained more than 90% energy absorption. Some cyclorotor WEC concepts are adapted from wind/air turbines, such as the Savonius [5,9], Darrieus and Wells rotors [10,11], for the marine environment. Despite some promising results, few devices have been developed beyond technology readiness level (TRL) 4 [12,13].…”