Publications

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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.

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.

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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.

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The total energy produced by a wind farm depends on the complex interaction of many wind turbines operating in proximity with the turbulent atmosphere. Sometimes, the unsteady forces associated with wind negatively influence power production, causing damage and increasing the cost of producing energy associated with wind power. Wakes and the motion of air generated by rotating blades need to be better understood. Predicting wakes and other wind forces could lead to more effective wind turbine designs and farm layouts, thereby reducing the cost of energy, allowing the United States to increase the installed capacity of wind energy. The Wind Energy Technologies Department at Sandia has collaborated with the University of Minnesota to simulate the interaction of multiple wind turbines. By combining the validated, large-eddy simulation code with Sandia’s HPC capability, this consortium has improved its ability to predict unsteady forces and the electrical power generated by an array of wind turbines. The array of wind turbines simulated were specifically those at the Sandia Scaled Wind Farm Testbed (SWiFT) site which aided the design of new wind turbine blades being manufactured as part of the National Rotor Testbed project with the Department of Energy.

Rotor design and analysis work has been performed to support the conceptualization of a wind tunnel test focused on studying wake dynamics. This wind tunnel test would serve as part of a larger model validation campaign that is part of the Department of Energy Wind and Water Power Program’s Atmosphere to electrons (A2e) initiative. The first phase of this effort was directed towards designing a functionally scaled rotor based on the same design process and target full-scale turbine used for new rotors for the DOE/SNL SWiFT site. The second phase focused on assessing the capabilities of an already available rotor, the G1, designed and built by researchers at the Technical University of München.

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The dynamic wake meandering model (DWM) is a common wake model used for fast prediction of wind farm power and loads. This model is compared to higher fidelity vortex method (VM) and actuator line large eddy simulation (AL-LES) model results. By looking independently at the steady wake deficit model of DWM, and performing a more rigorous comparison than averaged result comparisons alone can produce, the models and their physical processes can be compared. The DWM and VM results of wake deficit agree best in the mid-wake region due to the consistent recovery prior to wake breakdown predicted in the VM results. DWM and AL-LES results agree best in the far-wake due to the low recovery of the laminar flow field AL-LES simulation. The physical process of wake recovery in the DWM model differed from the higher fidelity models and resulted solely from wake expansion downstream, with no momentum recovery up to 10 diameters. Sensitivity to DWM model input boundary conditions and their effects are shown, with greatest sensitivity to the rotor loading and to the turbulence model.

In this paper, the effect of two different turbine blade designs on the wake characteristics was investigated using large-eddy simulation with an actuator line model. For the two different designs, the total axial load is nearly the same but the spanwise (radial) distributions are different. The one with higher load near the blade tip is denoted as Design A; the other is Design B. From the computed results, we observed that the velocity deficit from Design B is higher than that from Design A. The intensity of turbulence kinetic energy in the far wake is also higher for Design B. The effect of blade load distribution on the wind turbine axial and tangential induction factors was also investigated.

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