Power Properties of Two Interacting Wind Turbine Rotors

Abstract

In the current experiments, two identical wind turbine models were placed in uniform flow conditions in a water flume. The initial flow in the flume was subject to a very low turbulence level, limiting the influence of external disturbances on the development of the inherent wake instability. Both rotors are three-bladed and designed using blade element/lifting line (BE/LL) optimum theory at a tip-speed ratio, λ, of 5 with a constant design lift coefficient along the span, CL = 0.8. Measurements of the rotor characteristics were conducted by strain sensors installed in the rotor mounting. The resulting power capacity has been studied and analyzed at different rotor positions and a range of tip-speed ratios from 2 to 8, and a simple algebraic relationship between the velocity deficit in the wake of the front turbine and the power of the second turbine was found, when both rotors have the coaxial position.

Lab-scale measurements of wind farm blockage effects

“…they both follow the Reynolds scaling for incompressible flows. Aerodynamic experiments in water are thus not unusual and have been performed in both water flumes [13] as well as towing tanks [14], [15]. The single wind turbine rotors are represented by porous actuator discs with a solidity of σ = 57 % and a thrust coefficient of C T = 0.95.…”

Experiments on line arrays of horizontal-axis hydroturbines

“…Rotor performance was studied by measuring torque, M, and thrust, T, by strain sensors installed in the rotor mounting [25]. The voltage of the sensors was amplified by a preamplifier Scout 55, produced by Hootinger Baldwin Messtechnik, and was digitized by a NI6218 16 bit analog-to-digital converter unit produced by National Instruments Company.…”

Review of wake management techniques for wind turbines

“…The majority of studies are low‐fidelity simulations and analytical studies that use one of a few popular wake models to approximate the dynamics of wake–turbine and wake–wake interactions 32,34,36–38,41,42,45,49,53,54,59,61,63,65,66,68,70,74,75,77,82,85,89,91,93,94 . Some have used high‐fidelity computational fluid dynamics (CFD) 3,9,26,37,60,62,67,76,81,86,90 or specifically large eddy simulations (LES), 50,55 as well as scaled wind tunnel experiments, 33,39,40,47,48,52,56,69,79,91 and field tests 35,43,44,62,71 . The potential of AIC may have been inflated by the high number of low‐fidelity simulations, which likely report high power gains because they lack sufficient detail to capture critical wake dynamics.…”

“…As the wake expands, any turbine positioned directly downstream will not be able to harvest this excess energy. Another reason that so many studies may be inadequate indicators of AIC's potential is that they test it with a single column of turbines aligned to the inflow 26,33,35,37–40,42,48,50,55,56,59,62,63,65,66,68–70,74,76,77,79–82,85,89,91,92,94 . While such an arrangement does provide a worst‐case scenario as a baseline, it may also be a worst‐case scenario for AIC because downstream turbines are not optimally placed to harvest the excess energy left by upstream‐derated turbines.…”