Influences of yaw angle and turbulence intensity on the performance of a 20 kW in-stream hydrokinetic turbine

Abstract

Three-dimensional transient Computational Fluid Dynamics (CFD) simulations are performed to study the hydrodynamic performance of an ocean current turbine with a 3.0 m diameter 3-bladed rotor. Simulations are based on the Reynolds Averaged Navier-Stokes (RANS) equations and the shear stress transport k-ω turbulent model is utilized. The influence of yaw angle and upstream turbulence intensity (TI) on the turbine performance is studied. The CFD method is first validated using existing experimental data and good agreement is obtained. The performance of the turbine, including power, thrust and wake characteristics are then studied at different tip speed ratios (TSR). The turbine obtains a maximum coefficient of power (Cp) of 0.4642 at TSR=6 and the coefficient of thrust (Ct) increases over the entire evaluated TSR range to a value of 0.8788 at a TSR=10. Simulations are also performed at four different yaw angles, 0°, 5°, 10° and 15° which show that both Cp and Ct decrease as yaw angle increases. Finally simulations of three different TIs, 3%, 6% and 9%, are performed and analyzed. Results show that TI minimally affects Cp and Ct for the considered TI range, but greatly influences the downstream wake structure.

Characterization of the mean flow field in the far wake region behind ocean current turbines

“…This simulated 0.8 m rotor is designed to match the one used in experimental setup in Mycek et al (2014). Further validation of the CFD approach utilized here was carried by comparing the CFD approach with experimental setup in Bahaj et al (2007a, b) and is provided in detail in Tian et al (2016).…”

“…Using the data generation methodology described above, simulations are carried out for a reference 20 kW three bladed OCT model, with rotor diameter 3 m and hub diameter 0.6 m. The airfoil shapes used by this rotor are created from the FF-77-W airfoil type and other rotor details are available in Tian et al (2016). In addition to the 3 m rotor utilized to create the primary results presented in this paper, a 0.8 m rotor is simulated using the same CFD approach to validate the wake profile generated from the methodology presented here.…”

“…It provides accurate predictions of the onset and amount of flow separation under adverse pressure gradients, and has been successfully used in the CFD simulation of wind/water turbines (Lawson et al 2011;Lee et al 2015). The details of the CFD data generation methodology and validation based on experimental results available in Bahaj et al (2007a, b) are presented in Tian et al (2016), and briefly described here for the completeness of this paper.…”

“…The performance of turbine in terms of thrust and power coefficients were validated by simulating experimental setup of Bahaj et al (2007a, b), and this validation is presented in detail in Tian et al (2016). Likewise, the validation of wake profile generated by the CFD is carried out by comparing the wake profile of the CFD with the experimental studies presented in Mycek et al (2014).…”

Dynamic modeling of an underwater moored platform equipped with a hydrokinetic energy turbine

“…A previous study shows that the change in the rotor forces is less than 7.4% when the yaw angle is smaller than 15°. 26 Therefore, the effect of yaw on the rotor forces is neglected and the rotor forces at zero yaw state are used in this model. The force vector of the rotor is found by and C 2 , respectively, and ½x y , y y , z y T is the location of rotor in the UMP-fixed frame.…”