Laboratory experiments were performed on a geometrically scaled vertical-axis wind turbine model over an unprecedented range of Reynolds numbers, including and exceeding those of the full-scale turbine. The study was performed in the high-pressure environment of the Princeton High Reynolds number Test Facility (HRTF). Utilizing highly compressed air as the working fluid enabled extremely high Reynolds numbers while still maintaining dynamic similarity by matching the tip speed ratio (defined as the ratio of tip velocity to free stream, $\unicode[STIX]{x1D706}=\unicode[STIX]{x1D714}R/U$) and Mach number (defined at the turbine tip, $Ma=\unicode[STIX]{x1D714}R/a$). Preliminary comparisons are made with measurements from the full-scale field turbine. Peak power for both the field data and experiments resides around $\unicode[STIX]{x1D706}=1$. In addition, a systematic investigation of trends with Reynolds number was performed in the laboratory, which revealed details about the asymptotic behaviour. It was shown that the parameter that characterizes invariance in the power coefficient was the Reynolds number based on blade chord conditions ($Re_{c}$). The power coefficient reaches its asymptotic value when $Re_{c}>1.5\times 10^{6}$, which is higher than what the field turbine experiences. The asymptotic power curve is found, which is invariant to further increases in Reynolds number.
This study examined three-dimensional, volumetric mean velocity fields and corresponding performance measurements for an isolated vertical-axis wind turbine (VAWT) and for co- and counter-rotating pairs of VAWTs with varying incident wind direction and turbine spacings. The purpose was to identify turbine configurations and flow mechanisms that can improve the power densities of VAWT arrays in wind farms. All experiments were conducted at a Reynolds number of R e D = 7.3 × 10 4 . In the paired arrays, performance enhancement was observed for both the upstream and downstream turbines. Increases in downstream turbine performance correlate with bluff–body accelerations around the upstream turbine, which increase the incident freestream velocity on the downstream turbine in certain positions. Decreases in downstream turbine performance are determined by its position in the upstream turbine’s wake. Changes in upstream turbine performance are related to variations in the surrounding flow field due to the presence of the downstream rotor. For the most robust array configuration studied, an average 14% increase in array performance over approximately a 50° range of wind direction was observed. Additionally, three-dimensional vortex interactions behind pairs of VAWT were observed that can replenish momentum in the wake by advection rather than turbulent diffusion. These effects and their implications for wind-farm design are discussed.
Numerical investigation of the yawed wake and its effects on the downstream wind turbine J. Renewable Sustainable Energy 8, 033303 (2016) Increased power production is observed in downstream vertical-axis wind turbines (VAWTs) when positioned offset from the wake of upstream turbines. This effect is found to exist in both laboratory and field environments with pairs of co-and counter-rotating turbines, respectively. It is hypothesized that the observed production enhancement is due to flow acceleration adjacent to the upstream turbine due to bluff body blockage, which would increase the incident freestream velocity on appropriately positioned downstream turbines. A low-order model combining potential flow and actuator disk theory captures this effect. Additional laboratory and field experiments further validate the predictive capabilities of the model. Finally, an evolutionary algorithm reveals patterns in optimized VAWT arrays with various numbers of turbines. A "truss-shaped" array is identified as a promising configuration to optimize energy extraction in VAWT wind farms by maximizing the performance enhancement of downstream turbines. Published by AIP Publishing.
This study focuses on wind tunnel testing of a 3-bladed H-rotor vertical axis wind turbine (VAWT) under various conditions. Different performance metrics such as power coefficient (CP ), thrust load coefficient (CX ), and lateral load coefficient (CY ) are presented at four wind speeds. Parked loads, which are key parameters in designing VAWTs, are reported for the baseline case. Apart from presenting the benchmark results for the baseline model, the impact of two control strategies to boost the energy production of the VAWT are investigated. First, the effect of installing the plasma actuators on all blades is tested at four plasma input voltages. The results indicate that plasma actuators are an efficient approach to enhance the aerodynamic efficiency of VAWTs through modification of drag and lift loads acting on the blades. The second control strategy evaluated is intracycle RPM control. In this control method, the rotational speed of the turbine is varied with the azimuthal location of blades at each cycle so that the power production is increased. The results observed for this control strategy encourage further research development to expand the limited knowledge on its application for VAWTs.
Abstract. In this work, we extend the AeroDyn module of OpenFAST to support arbitrary collections of wings, rotors, and towers. The new standalone AeroDyn driver supports arbitrary motions of the lifting surfaces and complex turbulent inflows. Aerodynamics and inflow are assembled into one module that can be readily coupled with an elastic solver. We describe the features and updates necessary for the implementation of the new AeroDyn driver. We present different case studies of the driver to illustrate its application to concepts such as multirotors, kites, or vertical-axis wind turbines. We perform verification and validation of some of the new features using the following test cases: elliptical wings, horizontal-axis wind turbines, and 2D and 3D vertical-axis wind turbines. The wind turbine simulations are compared to existing tools and field measurements. We use this opportunity to describe some limitations of current models and to highlight areas that we think should be the focus of future research in wind turbine aerodynamics.
The aerodynamic effects of a dual plasma actuator arrangement on a GOE 735, 23% thickness airfoil, modeled after a Renewegy VP-20 wind turbine blade cross section, were studied. Experiments demonstrating actuator thrust capabilities are compared to previous reports to better understand the relationship between actuator geometry and performance. Characterizations of the effects of plasma actuators for aerodynamic flow control on the resultant coefficient of lift and drag curves are discussed at Re=1.50 × 10 5 . Additionally, the dual plasma actuator arrangement was tested at various applied voltage amplitudes, ranging from 1-9kVrms and frequencies ranging from 2-6kHz at Re=1.50 × 10 4 to study the aerodynamic effects and the electrical costs of this type of flow control. The voltage and current waveforms were sampled during 10s measurements so that the power dissipated by the actuators could be calculated. Relationships between the thrust produced by the actuators, the voltage amplitude and frequency, the coefficient of lift just before stall, and the dissipated power are discussed. In addition the effects of multiple actuators, the coefficient of drag just before stall, and the phase offsets of the voltage and current signals are discussed. NomenclatureU Windspeed, m/s f Frequency, Hz V Voltage, V T Thrust, g/m Re Reynolds Number C d Coefficient of drag C l Coefficient of lift α Angle of attack, deg P D Power dissipated, W Φ Phase angle between the current and the voltage AC signals, deg Subscripts rms Root mean squared value max Maximum value * Graduate Student, GALCIT, Downloaded by CORNELL UNIVERSITY on July 30, 2015 | http://arc.aiaa.org |
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