Advances in wind-plant control have often focused on more effectively balancing power between neighboring turbines. Wake steering is one such method that provides control-based improvements in a quasi-static way, but this does little to fundamentally change the wake recovery process, and thus, it has limited potential. This study investigates use of another control paradigm known as dynamic wake control (DWC) to excite the mutual inductance instability between adjacent tip-vortex structures, thereby accelerating the breakdown of the structures. The current work carries this approach beyond the hypothetical by applying the excitation via turbine control vectors that already exist on all modern wind turbines: blade pitch and rotor speed control. The investigation leverages a free-vortex wake method (FVWM) that allows a thorough exploration of relevant frequencies and amplitudes of harmonic forcing for each control vector (as well as the phase difference between the vectors for a tandem configuration) while still capturing the essential tip-vortex dynamics. The FVWM output feeds into a Fourier stability analysis working to pinpoint candidate DWC strategies suggesting fastest wake recovery. Near-wake length reductions of >80% are demonstrated, although without considering inflow turbulence. Analysis is provided to interpret these predictions considering the presence of turbulence in a real atmospheric inflow.
Nalu-Wind simulations of the neutral inflow Scaled Wind Farm Technology (SWiFT) benchmark were used to analyze which quantities of interest within the wind turbine wake and surrounding control volume are important in performing a momentum deficit analysis of the wind turbine thrust force. The necessary quantities of interest to conduct a full Reynolds-Averaged Navier-Stokes (RANS) formulation analysis were extracted along the control volume surfaces within the Nalu simulation domain over a 10 minute period. The thrust force calculated within the wake from two to eight diameters downstream using the control volume surfaces and the full RANS approach matched the thrust force that the wind turbine applied to the flowfield. A simplified one-dimension momentum analysis was included to determine if the inflow and wake velocities typically acquired during field campaigns would be sufficient to perform a momentum deficit analysis within a wind turbine wake. The one-dimensional analysis resulted in a 70% difference relative to the coefficient of thrust (Ct ) determined by the full RANS method at 2D downstream and a 40% difference from 5D to 8D, where D is the diameter of the turbine. This suggests that the quantities typically captured during field campaigns are insufficient to perform an accurate momentum deficit analysis unless streamwise pressure distribution is acquired, which reduced the relative difference to less than 10% for this particular atmospheric inflow.
Subscale wind turbines can be installed in the field for the development of wind technologies, for which the blade aerodynamics can be designed in a way similar to that of a full-scale wind turbine. However, it is not clear whether the wake of a subscale turbine, which is located closer to the ground and faces different incoming turbulence, is also similar to that of a full-scale wind turbine. In this work we investigate the wakes from a full-scale wind turbine of rotor diameter 80 m and a subscale wind turbine of rotor diameter of 27 m using large-eddy simulation with the turbine blades and nacelle modeled using actuator surface models. The blade aerodynamics of the two turbines are the same. In the simulations, the two turbines also face the same turbulent boundary inflows. The computed results show differences between the two turbines for both velocity deficits and turbine-added turbulence kinetic energy. Such differences are further analyzed by examining the mean kinetic energy equation.
The National Rotor Testbed (NRT) design verification experiment is the first test of the new NRT blades retrofitted to the existing Vestas V27 hub and nacelle operated at the Sandia Scaled Wind Farm Technology (SWiFT) facility. This document lays out a plan for pre-assembly, ground assembly, installation, commissioning, and flight testing the NRT rotor. Its performance will be quantified. Adjustments to torque constant and collective blade pitch will be made to ensure that the tip-speed-ratio and span-wise loading are as close to the NRT design as possible. This will ensure that the NRT creates a scaled wake of the GE 1.5sle turbine. Upon completion of this test, the NRT will be in an operational state, ready for future experiments. Page 3 of 30
A revised Sandia V27 reference model is provided for use with the wind turbine analysis code, FAST, incorporating refined parameters based on blade geometry measurements and performance data collected during the 2017 wake steering campaign at the Scaled Wind Farm Technology (SWiFT) site. The chord, twist, and airfoil section shapes were measured at five span locations on the blades of wind turbine WTGb1. The V27 AeroDyn file was updated with values equal to the measured chord and twist. The measured airfoil shapes deviated over the aft half of the chord compared to the original blade model NACA profiles. Differences in trailing edge camber were converted to an equivalent trailing edge flap effect calculated with thin airfoil theory. These mod- ified airfoil polars were updated in the V27 FAST model. The tip-speed-ratio and root bending moment were measured experimentally in the wake steering campaign at SWiFT on wind turbine WTGa1. The torque constant and collective pitch of the model were tuned so that the model output tip-speed-ratio and thrust, root bending moment matched the experiment across all wind speeds in region 2 operation with minimum error.
A new wind turbine blade has been designed for the National Rotor Testbed (NRT) project and for future experiments at the Scaled Wind Farm Technology (SWiFT) facility with a specific focus on scaled wakes. This report shows the aerodynamic design of new blades that can produce a wake that has similitude to utility scale blades despite the difference in size and location in the atmospheric boundary layer. Dimensionless quantities circulation, induction, thrust coefficient, and tip-speed-ratio were kept equal between rotor scales in region 2 of operation. The new NRT design matched the aerodynamic quantities of the most common wind turbine in the United States, the GE 1.5sle turbine with 37c model blades. The NRT blade design is presented along with its performance subject to the winds at SWiFT. The design requirements determined by the SWiFT experimental test campaign are shown to be met.