Influence of turbulence on the wake of a marine current turbine simulator

Abstract

Marine current turbine commercial prototypes have now been deployed and arrays of multiple turbines under design. The tidal flows in which they operate are highly turbulent, but the characteristics of the inflow turbulence have not being considered in present design methods. This work considers the effects of inflow turbulence on the wake behind an actuator disc representation of a marine current turbine. Different turbulence intensities and integral length scales were generated in a large eddy simulation using a gridInlet, which produces turbulence from a grid pattern on the inlet boundary. The results highlight the significance of turbulence on the wake profile, with a different flow regime occurring for the zero turbulence case. Increasing the turbulence intensity reduced the velocity deficit and shifted the maximum deficit closer to the turbine. Increasing the integral length scale increased the velocity deficit close to the turbine due to an increased production of turbulent energy. However, the wake recovery was increased due to the higher rate of turbulent mixing causing the wake to expand. The implication of this work is that marine current turbine arrays could be further optimized, increasing the energy yield of the array when the site-specific turbulence characteristics are considered.

Effects of turbulence on tidal turbines: Implications to performance, blade loads, and condition monitoring

“…On the other hand, large scale turbulence interacts directly with the body itself and the wake as a whole. Similar effects have been found using porous disc rotor simulators [10], and the interaction of turbulence scale with the wake observed using Large Eddy Simulations with actuator discs [11]. It was found that small scale turbulence reduced the velocity deficit in the wake of the actuator disc, but did not significantly affect the wake expansion or wake recovery.…”

“…Previous investigations have shown how the thrust coefficient, or mean (time averaged) thrust force, of a porous disc rotor simulator can vary by over 20% in turbulent flows with different turbulence characteristics [10]. Further, numerical simulations have shown how turbulence affects the wake recovery behind an actuator disc turbine representation [11]. Studies using model turbine rotors have also shown significant variations when operated in flows with different turbulence intensities [12]- [14].…”

“…For example, it is possible to have 2 different flows with turbulence intensities of 10%, but one has large scale, low frequency turbulent structures, and the other with small scale, high frequency structures. Previous investigations have found the integral length scale to be an important parameter resulting in significant variations in thrust and wake recovery [10], [11].…”

On the Evolution of the Integral Time Scale within Wind Farms

“…Furthermore, Singh et al [29] pointed out that wind turbines reduce the intermittency and asymmetry in the wake by breaking and deflecting the large-scale flow structures; the non-local transfer between large and small scales is strongly attenuated, resulting in the more homogenized velocity structure as compared to the base flow. Numerical simulations by Blackmore et al [30] showed that the increase in Λ u of the incoming flow might speed up the wake recovery and increase the wake span.…”

Experimental demonstration of performance of a vertical axis marine current turbine in a river

“…1,2 Several marine current power research projects are underway world-wide, commercial as well as academic. 3,4 Much work has been or is being done on scale-model experiments and numerical modeling, [5][6][7][8] and investigations have been and are being performed outside the laboratories as well. 9,10 The water flow speed at a potential marine current power site is an important factor in determining the possible energy yield from the site.…”