effects of surge motion on floating horizontal axis tidal turbines

Abstract

Wave induced motions due to actual sea state conditions will impact the performance of floating horizontal axis tidal turbine systems. This paper presents the results from numerical simulations of a 3-bladed horizontal axis tidal turbine oscillating in surge motion in a moving reference frame. The optimum tip-speed ratio, λ = 4.4 and k-ω SST turbulence model were used in the present study. The Navier-Stokes equation was modified by adding an inertial term to the equation and the Dirichlet boundary condition was also modified in order to simulate in the moving reference frame. The surge oscillations were parameterised in terms of the ratio of surge amplitude to rotor radius, A*, and the ratio of oscillation frequency to the rotational frequency of the rotor, ω*. A series of tests were conducted to study the effect of each parameter on the hydrodynamic performance of the tidal turbine. The results show that stall can occur on the blade when the velocity relative to the rotor is sufficiently high. In certain cases, negative thrust and power coefficients were observed when the velocity relative to the rotor is low. The fluctuation in blade loading increases together with the amplitude and frequency of oscillation, which will contribute to the fatigue of the rotor.

A Numerical Study on the Hydrodynamics of a Floating Tidal Rotor Under the Combined Effects of Currents and Waves

“…The bullet points show mean quantities, while bars The thrust plots show that mean values are not significantly influenced by waves nor by platform motions. This is in agreement with the results presented by, e.g., Galloway et al (2014), de Jesus Henriques et al (2014), and Guo et al (2018a, for cases of rotors operating under the influence of surface waves, and by Osman and Willden (2020) and Osman et al (2019) for rotors under prescribed motions. The load fluctuation magnitude, however, varies between cases as a function of wave period.…”

“…The motion of a rotor in some of these degrees of freedom, decoupled from waves, has been studied through the simulation of rotors under prescribed motions. Osman et al (2019), Osman and Willden (2020), for example, studied a tidal rotor under prescribed surge and pendular motions, respectively, using Reynolds-Averaged Navier Stokes (RANS) CFD simulations. Similar to the cases above of rotors under the influence of surface waves, the studies on prescribed motions demonstrated that mean loads are largely unaffected as long as no significant flow separation is observed on the blades.…”

Hydrodynamics and Wake Flow Analysis of a Floating Twin-Rotor Horizontal Axis Tidal Current Turbine in Roll Motion

“…The axial damping coefficient of the turbine was derived by using the least squares method and was found to have no significant correlation with the amplitude and frequency of the surge motion. Osman [13] obtained similar results in their study. Jiang [14] studied the load variation of a vertical-axis tidal current turbine under the coupling effect of roll and yaw.…”

The Fluid Mechanics of Tidal Stream Energy Conversion

“…Surge oscillations result in velocity perturbations that are uniform across the rotor (Zhang et al 2015), whereas platform pitching motions create a spatially varying velocity perturbation. Turbine blades may temporarily stall under large platform motions, which tend to reduce the mean thrust and power compared to the nonoscillating case and significantly increase fatigue loads (bin Osman et al 2019). The added mass of turbines oscillating in surge has been found to be modest (Whelan et al 2009, bin Osman et al 2019.…”

“…Turbine blades may temporarily stall under large platform motions, which tend to reduce the mean thrust and power compared to the nonoscillating case and significantly increase fatigue loads (bin Osman et al 2019). The added mass of turbines oscillating in surge has been found to be modest (Whelan et al 2009, bin Osman et al 2019.…”