Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session C09: Turbines: General |
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Chair: Brent Houchens, Sandia National Laboratories Room: 213 |
Sunday, November 24, 2019 8:00AM - 8:13AM |
C09.00001: Influence of Near-blade Hydrodynamics on Cross-flow Turbine Performance Abigale Snortland, Brian Polagye, Owen Williams Cross-Flow turbines are a promising technology for harvesting kinetic energy from wind and water currents. The hydrodynamics are complex and rapid changes in angle of attack lead to phenomena such as dynamic stall and periodic vortex shedding. A robust understanding of local flow features at the turbine blades and their impact on phase-averaged performance is essential for turbine design and can inform control strategy development. Phase-averaged 2D planar PIV data is examined for both optimal (maximum power generation) and sub-optimal rotation rates over the entire sweep of a two-bladed, cross-flow turbine. The phase and rotation-rate dependent, near-blade/wake hydrodynamics are examined in concert with phase-averaged performance data. The duration/severity of flow reversal on, and detachment from, the blades appear critical to average performance. Strong stall and vortex interactions occur over most of the turbine rotation for the sub-optimal case, possibly producing parasitic forces that outweigh any increases in lift from the leading-edge vortex. At the optimal rotation rate, vortex shedding on the upstream blade is significantly delayed, and the downstream blade is weakly stalled. This likely explains the difference in power output between the two cases. [Preview Abstract] |
Sunday, November 24, 2019 8:13AM - 8:26AM |
C09.00002: Improving the accuracy of wind farm LES using filtered actuator disk theory corrections Carl Shapiro, Dennice Gayme, Charles Meneveau The utility of large eddy simulations (LES) of large wind farms that employ the actuator disk model (ADM) are limited by over-prediction of power that can exceed 10\% at typical resolutions. Computational restrictions require spatial filtering of the actuator disk thrust force, which is distributed equally across the swept area of the rotor blades, resulting in an under-prediction of the shed vorticity. The filtered ADM, which models the wind turbine wake as concentric semi-infinite vortex cylinders, provides a basis for analytically correcting this error in simulation. When compared to simulations with various filter widths and grid sizes, the filtered ADM accurately predicts the power coefficient measured in simulations. An analytic correction factor is then derived from the filtered ADM that collapses the power coefficient measured in simulations onto the theoretical axial momentum theory predictions. This approach eliminates the need for highly refined numerical grids or empirical correction factors. [Preview Abstract] |
Sunday, November 24, 2019 8:26AM - 8:39AM |
C09.00003: LES of microscale winds in complex configurations. Laurent Bricteux, Stephanie Zeoli, Moncef Gazdallah, Paulina Pianko-Oprych, Gregoire Leroy, Pierre Benard This contribution concerns wall modeled large eddy simulations (WMLES) of turbulent winds in complex geometries that are relevant for wind energy problems: either in the built environment (e.g. generic buildings) or complex terrains (e.g. Askervein Hill). This work is performed in the framework of developing simplified operational models to be used for wind turbine siting. It is proposed to investigate the influence of the wall modeling strategy and the turbulent inflow boundary condition on the flow diagnostics relevant for wind turbine siting (local velocity and turbulence profiles). The validity and quality of an original turbulence inflow generation method are also assessed. This boundary condition is based on the algorithm of Mann and generates realistic atmospheric turbulence with a prescribed spectrum and lengthscale. [Preview Abstract] |
Sunday, November 24, 2019 8:39AM - 8:52AM |
C09.00004: Power measurements in a scale model wind farm: Results from varying array size, arrangement, spacing, and setpoints Dan Houck, Edwin Cowen The current trend in wind energy research is to optimize wind farms as opposed to optimizing individual turbines. There is also an emerging idea to consider the wind turbines themselves as actuators that can be used to intentionally and beneficially manipulate the flow to improve the power output of the wind farm. To this end, we completed a series of experiments with an array of 18 model-scale wind turbines in a 2 m wide flume testing changes in the number, arrangement, and spacing of the turbines as well as the setpoint, or power production, of each turbine. Each treatment case is compared to a similar control case that was arranged and operated more conventionally with all turbines attempting maximum power production. A highly accurate torque transducer provides calibrations allowing non-intrusive mechanical power measurements of each turbine. Comparisons are made on the basis of overall power output, array efficiency (total power output of the N-turbine array divided by N of an upstream turbine operating at max power), and power density (power per area). Particle image velocimetry (PIV) further reveals the fluid dynamics at work to create any improvements in power. [Preview Abstract] |
Sunday, November 24, 2019 8:52AM - 9:05AM |
C09.00005: Flow Instabilities during High-performance Operation of a Wind Energy Harvester with No External Moving Parts Brent Houchens, David Marian, Suhas Pol, Carsten Westergaard A novel wind energy harvester with no external moving parts is demonstrated at one-third scale (0.5-meter chord) in wind tunnel tests. The device uses mirrored airfoil-pairs to create suction. This pulls air out from ducts internal to the foils, through air-jet orifices on the low-pressure sides of the foils, and into the external incident wind. Power is transmitted pneumatically through the center of the foils to an internal turbine-generator. In the high-performance operating mode at high angle-of-attack, a mechanical power transmission of nearly one-half of the Betz limit is achieved. However, this high angle-of-attack configuration is susceptible to aero-acoustic instabilities which can diminish the performance to as low as one-sixth of the Betz limit. These instabilities are investigated here for a configuration with all air-jets covered. Pressure measurements are made on the low-pressure sides of the foils and the break in symmetry associated with the instability is documented. Particle image velocimetry is used to characterize the flow field before and after onset of the instability. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. [Preview Abstract] |
Sunday, November 24, 2019 9:05AM - 9:18AM |
C09.00006: Experimental comparison of HAWTs with hydrostatic and regular transmissions Helber Antonio Esquivel-Puentes, Andrea Vacca, Leonardo P Chamorro, Jose Garcia-Bravo, Humberto Bocanegra-Evans, David Warsinger, Walter Gutierrez, Luciano Castillo The performance of a horizontal axis wind turbine (HAWT) with hydrostatic transmission was compared with that of a standard unit using well-controlled experiments. The power output of the hydrostatic unit is used for electricity generation, and/or reverse osmosis to obtain fresh water. Furthermore, the hydrostatic transmission allows for moving the major electro-mechanical components located in the hub to the ground level. The associated changes resulted in reductions of approximately 30{\%} of the total mass of the unit, and of about 7 to 14{\%} of the cost of the energy. The reconfiguration of the structure of the turbine also implied changes in the response of the system to turbulence. We assessed such effects across scales considering changes in the transfer function of the spectrum of the power output, following Tobin \textit{et al} (2015). [Preview Abstract] |
Sunday, November 24, 2019 9:18AM - 9:31AM |
C09.00007: Reliability of Long-term Lidar-based Wind Measurements for Various Wind Energy Applications Jay Prakash Goit, Susumu Shimada, Tetsuya Kogaki In this work, we conduct a long-term measurement campaign (approximately one year) using a profiling Lidar, in order to investigate whether Lidars can be used as a reliable alternative to meteorological masts for wind energy applications. It is found that the Lidar-measured wind speed showed good agreement with those measured using sonic anemometers mounted to the neighboring meteorological mast, with the coefficient of determination ($R^2>0.99$). However, comparison of the standard deviations shows larger degree of variations, with $R^2$ between 0.92 and 0.97. Turbulence intensities computed for the 90th percentile of the standard deviation show that the Lidar-measured turbulence intensities are larger by roughly 2\% than those measured by the sonic anemometer. But the gust factors for peak wind speeds converge roughly to 1.9 during strong wind speed for both the devices. Finally, wind speed and turbulence distribution for the Lidar and sonic anemometer are used to compute fatigue load for NREL 5-MW reference wind turbine using aeroelastic simulation. The 20 years lifetime DELs for the Lidar wind speed are higher than those for the sonic anemometer wind speeds, by 6\% for the blade root bending moment and by 13\% for the tower based bending moment. [Preview Abstract] |
Sunday, November 24, 2019 9:31AM - 9:44AM |
C09.00008: Actuator-line simulations of wind turbines with block-structured adaptive mesh refinement Mahesh Natarajan, Hariswaran Sitaraman, Shreyas Ananthan, Michael Alan Sprague Wind turbine parametrization methods such as the actuator disk (ADM) or actuator line methods (ALM) have shown good promise in determining power generation and loads on the turbine blades. However, performing such simulations in a cost-effective manner is a challenging task, due to the wide range of scales involved. The scales in the atmospheric boundary layer (ABL) range from ~ 1 km to scales in the wake region that are ~1 m. Adaptive mesh refinement techniques are well suited for this scenario, and will enable well-resolved simulations that can capture turbulent structures across multiple length scales. In this work, we implement an ALM model in two frameworks - a compressible and an incompressible flow solver - both developed within the block-structured adaptive mesh refinement (AMR) framework of AMReX [1], and compare their performance. Computational scaling studies are done on a single turbine configuration, and compared with Nalu-Wind [2] - an unstructured CFD solver for wind turbine simulations. [Preview Abstract] |
Sunday, November 24, 2019 9:44AM - 9:57AM |
C09.00009: Biomimetic individual pitch control for wind turbines Marion Coquelet, Laurent Bricteux, Maxime Lejeune, Philippe Chatelain Individual Pitch Control (IPC) has proved efficient in reducing fatigue loads on wind turbines. As 1P (once-per-revolution) blade loads are significant due to wind shear or tower shadow effect, their alleviation implies a rhythmic behavior in the changes of the blade pitch angles. This work relies on Large Eddy Simulations (LES) to demonstrate the effectiveness of a biomimetic architecture for IPC. The high-fidelity simulation of the flow physics is essential to assess the performances of the controller. It is performed by an in-house lifting-lines-enabled Vortex Particle-Mesh method, dealing with synthetic turbulence and wind shear at the inflow. The individual pitch controller is based on Central Pattern Generators (CPGs). CPGs produce, from very simple inputs, rhythmic outputs that drive repetitive motions like walking or breathing. The specificity of these networks is their ability to operate autonomously. They are here implemented as coupled non-linear oscillators, capable of producing coordinated rhythmic patterns and driven by a knowledge of the upstream flow conditions. The latter are reconstructed online by an Extended Kalman Filter processing the loads experienced by the individual blades. [Preview Abstract] |
Sunday, November 24, 2019 9:57AM - 10:10AM |
C09.00010: Comparison of theory and large-eddy simulations with experiments of flow over a wing Luis Martinez, Marc Henry de Frahan, Ganesh Vijayakumar, Shreyas Ananthan In this work, we compare experimental measurements of the force distribution along the span of a NACA-0015 wing at low angles of attack to: 1) filtered-lifting-line-theory, 2) large-eddy simulations (LES) using the actuator line model, and 3) blade resolved detached-eddy simulations (DES). These techniques are often used to model wind turbine blades in computational fluid dynamics. Filtered-lifting-line-theory is a semi-analytical solution to the blade forces along the blade from the actuator line model. The results from filtered-lifting-line-theory and LES using the actuator line model are in excellent agreement, as expected, and agree well with the measurements. The results suggest that when computing the forces along the blade, filtered-lifting-line-theory, LES using the actuator line model, and blade resolved DES agree well with the experiment and the differences between each method are small. However, when comparing the flow fields downstream, blade resolved simulations are able to accurately capture the tip-vortex, whereas the actuator line model cannot always capture the flow details from the tip vortex. [Preview Abstract] |
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