CFD Validation of Moment Balancing Method on Drag-Dominant Tidal Turbines (DDTTs)

Abstract

Current performance analysis processes for drag-dominant tidal turbines are unsuitable as disk actuator theory lacks support for varying swept blockage area, bypass flow downstream interaction, and parasitic rotor drag, whereas blade element momentum theory is computably effective for three-blade lift-dominated aerofoil. This study proposes a novel technique to calculate the optimal turbine tip speed ratio (TSR) with a cost-effective and user-friendly moment balancing algorithm. A reliable dynamic TSR matrix was developed with varying rotational speeds and fluid velocities, unlike previous works simulated at a fixed fluid velocity. Thrust and idle moments are introduced as functions of inlet fluid velocity and rotational speed, respectively. The quadratic relationships are verified through regression analysis, and net moment equations are established. Rotational speed was a reliable predictor for Pinwheel’s idle moment, while inlet velocity was a reliable predictor for thrust moment for both models. The optimal (Cp, TSR) values for Pinwheel and Savonius turbines were (0.223, 2.37) and (0.63, 0.29), respectively, within an acceptable error range for experimental validation. This study aims to improve prevailing industry practices by enhancing an engineer’s understanding of optimal blade design by adjusting the rotor speed to suit the inlet flow case compared to ‘trial and error’ with cost-intensive simulations.

The Biffis Canal Hydrodynamic System Performance Study of Drag-Dominant Tidal Turbine Using Moment Balancing Method

“…Previous works investigated moment analysis of a single turbine in either horizontal or vertical axis configuration by utilizing a fixed inlet flow speed scheme. The TSR ranges of this study follow a dynamic TSR matrix for the simulations as studied in [18]. In this study, the simulation algorithm aims to investigate the net moment of rotating machinery under different BCs, specifically the rotating speed and flow velocity.…”

“…The previous study tested the rectangular channels with seawater continua for Pinwheel and Savonius turbines [18]. The geometries of the Pinwheel and Savonius turbines were developed using SolidWorks and subsequently imported into the Star-CCM+ platform.…”

“…This study investigated the models by multiplying the Savonius turbine's blade radius by a factor of 3.58 for an equal blade and Ref. [18] utilised the Savonius blade and channel area from [27] to calculate the blockage and aspect ratio with their definition equation shown as Equations ( 1) and (2). The aspect ratio is defined as the ratio of channel width to channel height, and the blockage ratio is the ratio of the rotor blades' sweep area to the channel cross-section area.…”