Abstract
The objective of this paper is to numerically investigate the effects of the atmospheric boundary layer on the aerodynamic performance and loads of a novel dual-rotor wind turbine (DRWT). Large eddy simulations are carried out with the turbines operating in the atmospheric boundary layer (ABL) and in a uniform inflow. Two stability conditions corresponding to neutral and slightly stable atmospheres are investigated. The turbines are modeled using the actuator line method where the rotor blades are modeled as body forces. Comparisons are drawn between the DRWT and a comparable conventional single-rotor wind turbine (SRWT) to assess changes in aerodynamic efficiency and loads, as well as wake mixing and momentum and kinetic energy entrainment into the turbine wake layer. The results show that the DRWT improves isolated turbine aerodynamic performance by about 5%–6%. The DRWT also enhances turbulent axial momentum entrainment by about 3.3 %. The highest entrainment is observed in the neutral stability case when the turbulence in the ABL is moderately high. Aerodynamic loads for the DRWT, measured as out-of-plane blade root bending moment, are marginally reduced. Spectral analyses of ABL cases show peaks in unsteady loads at the rotor passing frequency and its harmonics for both rotors of the DRWT.
Highlights
Modern utility-scale horizontal axis wind turbine (HAWT) rotor blades are aerodynamically optimized in the outboard region, whereas the blade root region is designed primarily to withstand structural loads
A cartoon of the dual-rotor wind turbine (DRWT) technology proposed by Rosenberg et al [16]
We analyze the effect of the atmospheric boundary layer (ABL) on blade root loss, wake mixing and aerodynamic loads
Summary
Modern utility-scale horizontal axis wind turbine (HAWT) rotor blades are aerodynamically optimized in the outboard region, whereas the blade root region is designed primarily to withstand structural loads. Very high thickness-to-chord ratio airfoils, which are aerodynamically poor, are used in the blade root region to provide structural integrity. Up to 5% loss in wind energy extraction capability is estimated to occur per turbine due to this compromise [1]. Occurs even in turbines that operate in isolation, i.e., with no other turbine nearby. Most utility-scale turbines are deployed in clusters, with multiple turbines operating in proximity of each other. Array interference (wake) losses resulting from aerodynamic interaction between turbines in wind farms have been measured to range between 8% and 40% depending on wind farm location, farm layout/wind direction and atmospheric stability condition [2]
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