Flow separation impacts on the hydrodynamic performance analysis of a marine current turbine using CFD

Abstract

Although there are different strategies to control the operation of marine turbines, the so-called ‘stall-regulated strategy’ is one of the most widely used and mature control strategies. Since the stall phenomenon is closely related to flow separation around the turbine blades the treatment of this separation requires great care during the design and performance analysis of turbines when using computational fluid dynamics (CFD). This study investigates appropriate methodologies and approaches to simulate the hydrodynamic performance of horizontal marine turbines with a specific emphasis on the flow separation phenomena. The well-known viscous flow solver ANSYS-CFX was employed as the main CFD code to predict the power extraction coefficient of these turbines. The investigations were carried out by using both numerical and experimental methods applied on tidal stream turbine models tested in the Emerson Cavitation Tunnel of Newcastle University, UK and the circulating water channel of Harbin Institute of Technology, China. The measured power extraction coefficients generally agreed well with the numerically predicted ones except for one of the models with the lower pitch angle which displayed large discrepancies over the entire operating range. The detailed flow analyses from the CFD studies with this turbine and other model at higher pitch angles revealed that large-scale detached vortices developed downstream of the model with the lower pitch angle may have contributed to this large discrepancy. The study therefore draws attention to the importance of the combined use of the CFD and model test-based approaches in the design and performance analysis of marine turbines.

Cavitation observations and noise measurements of horizontal axis tidal turbines with biomimetic blade leading-edge designs

“…In this paper a typical three bladed HATT was chosen for the study. This turbine model was designed and tested during a previous project (Wang et al, 2007) and validated by a CFD study (Shi et al, 2013). The main parameters of the notional full-scale design are given in Table 1.…”

Experimental study of wake characteristics in tidal turbine arrays

“…14 The downstream turbine operated at increased TSR due to the reduced inflow velocity and 15 showed lower performance with higher variations (Fig. 5) however, the turbine blade design 16 was shown previously to maintain high and practically constant CT values over a range of TSR 1 expected to be encountered by the upstream and downstream turbine [27]. The detailed 2 performance of array turbines will be further investigated further numerically.…”

Optimal design of a thin-wall diffuser for performance improvement of a tidal energy system for an AUV

“…Reynolds number in the ECT is almost three times higher than in the HIT water channel the impact of the Reynolds number on the results appeared to be limited. Only 0.75% difference can be found at TSR=5.5 when the turbine reached to the maximum power coefficient (Shi et al, 2013).…”

“…This was a 3-bladed horizontal axial turbine using symmetrical and bi-directional airfoil blade sections. These sections are classified as BDA65-21 and BDA66-12 (Guo et al, 2013;Shi et al, 2013), which were adopted from NACA 65-21 and NACA 66-12, respectively, as shown in Fig.2. The open water performance of the turbine was verified experimentally using a 300mm diameter model turbine which was initially tested in the Emerson Cavitation Tunnel (ECT) of Newcastle University, UK (Atlar, 2011) and later in the circulating water channel of Harbin Institute of Technology (HIT), in China.…”