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 Q14: Wind Turbines: Vertical Axis |
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Chair: Mark Miller, Pennsylvania State University Room: 307/308 |
Tuesday, November 26, 2019 7:45AM - 7:58AM |
Q14.00001: Blade-Wake Interactions in a Vertical Axis Wind Turbine Sangwoo Ahnn, Hyeongmin Kim, Sehyeong Oh, Haecheon Choi We investigate the flow characteristics of a vertical axis wind turbine (VAWT) and its aerodynamic performance using large eddy simulation with an immersed boundary method. The VAWT considered in this study consists of three blades, and the Reynolds number is 80,000 based on the rotor diameter and free-stream velocity. The simulation results show that each blade interacts with the wakes generated by the preceding blade and also by itself in the downwind region. To examine the effect of these blade-wake interactions on the aerodynamic performance, we simulate the flows with one blade only and with two blades, respectively. The blade performance significantly deteriorates in the upwind region due to the wake induced by the preceding blade. In the downwind region where the blade performance is poor, each blade interacts with its own wake and the wake from the preceding blade, but these blade-wake interactions rather improve the aerodynamic performance of each blade. As the tip speed ratio increases, the preceding blade highly influences the performance of the following blade, but does not much on the second following blade. [Preview Abstract] |
Tuesday, November 26, 2019 7:58AM - 8:11AM |
Q14.00002: A design of active flow control on vertical-axis wind turbines based on resolvent analysis Hsieh-Chen Tsai We design an active flow control on vertical-axis wind turbines (VAWT) combining the resolvent analysis and direct numerical simulations (DNS). The immersed boundary projection method is used to simulate the two-dimensional incompressible flow around a NACA0018 three-bladed VAWT at low Reynolds numbers. Localized body forces are placed on the surfaces of the turbine blades to mimic the streamwise plasma jets generated by Dielectric barrier discharge (DBD) actuators. The optimal actuator locations and the optimal actuation frequencies at various Reynolds numbers are determined by the resolvent analysis of the mean flow around the VAWT. Preliminary results show that by removing wake-capturing vortical structures observed in previous studies, the active flow control successively enhances the average torque generated by turbine blades. [Preview Abstract] |
Tuesday, November 26, 2019 8:11AM - 8:24AM |
Q14.00003: Performance Analysis of Flexible-Bladed Vertical-Axis Wind Turbines Lalit Roy, David MacPhee In this study, airfoil lift and drag coefficient data are used in a blade element momentum theory-based double multiple stream tube (DMST) model to assess performance of a chord-wise flexible vertical-axis wind turbine (VAWT). Wind-tunnel experiments are performed for rigid and flexible airfoils, over a range of Reynolds numbers, and performance improvements in terms of lift and drag coefficients are discussed. Airfoil simulations are performed using the OpenFOAM framework to help identify any mechanisms of airfoil performance improvement. Finally, airfoil lift and drag data are used with the aforementioned DMST model to investigate any performance improvements in VAWT performance through the use of flexible blades. [Preview Abstract] |
Tuesday, November 26, 2019 8:24AM - 8:37AM |
Q14.00004: 2D CFD study of Darrieus type straight single bladed VAWT using OpenFOAM Asmelash Haftu, Shivasubramanian Gopalakrishnan, Prabhu Ramachandran Vertical Axis Wind Turbines (VAWTs) employ one or more, straight or curved blades which rotate parallel to the axis of rotation. Blade arrangement creates complex aerodynamics and unsteadiness in the flow. The objective of this study is to demonstrate a CFD model for simulating VAWT blade traversing circular orbit and describe the unsteady aerodynamics data. The model geometric configuration consists of rotor-core and turbine diameters as 1.5m and 1.22m respectively for NACA0015 airfoil with chord length 0.1542. Inlet velocity of water 0.091m/s yields a blade Reynolds number of 67,000 for a tip speed ratio equal to 5. Our mesh independent test suggests about 200k cells (snappyHexMesh), compromising between accuracy, stability, and cost. The pimpleDyMFoam (compatible with moving meshes) is a suitable pressure based OpenFOAM solver for the unsteady 2D simulation with second-order accuracy in space and time. Nondimensional normal and tangential force components were computed and compared well with the experimental work of Oler JW. et al. (1983). The methodology presented here can be used as a guideline for design, and CFD analysis of single to multi-bladed VAWTs with fewer cells than reported earlier. [Preview Abstract] |
Tuesday, November 26, 2019 8:37AM - 8:50AM |
Q14.00005: Impact of different strut geometries on the performance of H-Darrieus vertical-axis turbines Thierry Villeneuve, Guy Dumas Previous studies have shown that the performance of H-Darrieus vertical-axis turbines are highly sensitive to the blades mounting structure. More precisely, the struts, that are supporting the turbine blades, are detrimental to the power extraction. Indeed, the presence of the struts leads to an additional viscous drag contribution for the moving blades that results in a negative torque contribution at the turbine shaft. In addition to this added drag contribution, the struts also affect the flow field within the turbine, and thus, the forces acting on the turbine blades. In order to better understand these interactions between the blades and the struts, URANS and DDES numerical simulations are conducted for an H-Darrieus vertical-axis turbine with different strut configurations at a high Reynolds number. The results obtained from these simulations show that the struts affect importantly the spanwise distribution of the forces on the turbine blades. Moreover, the numerical simulations provide useful insights into the flow field within the turbine that can help to develop a strut geometry that could extract energy from the flow while minimizing its interference with the blade, and thus, contributing positively to the turbine efficiency. [Preview Abstract] |
Tuesday, November 26, 2019 8:50AM - 9:03AM |
Q14.00006: A Wake in the Middle of the Night: 3D-PTV Measurements around Full-Scale Vertical-Axis Wind Turbines Nathaniel Wei, Ian Brownstein, Jennifer Cardona, Michael Howland, John Dabiri Studies of the wake dynamics of wind turbines are critical for the design and optimization of wind farms in order to minimize wake losses and maximize power density. To observe the inherently three-dimensional flow structures in the wakes of full-scale vertical-axis wind turbines (VAWTs), a volumetric particle-tracking velocimetry method was developed for field experiments at the Field Laboratory for Optimized Wind Energy (FLOWE) in Lancaster, CA, using six cameras and artificial snow as tracer particles. Velocity and vorticity fields extending up to three turbine diameters into the wake were measured around isolated 2-kW VAWTs: one with five straight blades, and another with three helical blades. Two tip-speed ratios were examined for each turbine. The 3D flow measurements allowed the dynamics of vortical structures in the streamwise, transverse, and wall-normal directions to be analyzed. Additionally, significant differences in wake geometry between the straight- and helical-bladed turbines were observed, which can be explained using a simple vortex-line model. These results help clarify mechanisms responsible for wake recovery in VAWTs, and thus have implications for wind-farm design. [Preview Abstract] |
Tuesday, November 26, 2019 9:03AM - 9:16AM |
Q14.00007: Vertical Axis Wind Turbine Design Using Design-by-Morphing and Bayesian Optimization Haris Moazam Sheikh, Philip S Marcus Vertical Axis Wind Turbines (VAWTs) have not been commercialized due to their low Coefficients of Performance (Cp) compared to Horizontal Axis Wind Turbines (HAWTs). However, their low Cp's are likely due to the historical lack of systematic optimization. Recent studies, however, have shown that VAWTs can outperform HAWTs in closely packed arrays in terms of energy produced/area. This observation, combined with their low manufacturing and maintenance costs, and versatility, have sparked renewed interest in VAWTs. In this work, we optimize a VAWT and its concentrator with two techniques: Design by Morphing (DbM), which is a novel design method, and Bayesian optimization. With DbM, the shapes of the VAWT blades and concentrators are determined by morphing baseline shapes together, and the weights of the shapes used in the morph are part of a large Degree of Freedom (DoF) design space. Searching for the optimal design in the high DoF space is not possible using conventional optimization techniques due to the high cost of data for this problem, (i.e., computing or experimentally measuring the Cp of a VAWT). Using Bayesian optimization however, a 6-DoF space is optimized with only 1000 CFD-computed data points and produces an optimized VAWT along with its concentrator. [Preview Abstract] |
Tuesday, November 26, 2019 9:16AM - 9:29AM |
Q14.00008: Vertical Axis Wind Turbine Performance Scaling at High Reynolds Numbers with Varying Solidity Mark Miller, Alexander Pique, Subrahmanyam Duvvuri, Marcus Hultmark The large physical size and numerous design configurations of the Vertical Axis Wind Turbine have made it difficult to fully characterize the operational envelope of these machines. Laboratory experiments have been performed on a limited number of configurations due to the high-cost associated with testing full-scale models in large wind tunnel facilities. Ongoing work at Princeton University and Penn State has aimed to examine VAWT operation in detail using the controlled conditions of the laboratory, while simultaneously matching the full-scale aerodynamic parameters of interest: the Reynolds number and the tip speed ratio. To achieve this, a specialized, high-pressure wind tunnel facility has been employed to reach very large Reynolds numbers of 5 million, based on diameter and free-stream conditions, independent of changes to the tip speed. Results are presented from a 10 cm diameter model at many different tip speed ratios and Reynolds numbers which match and even exceed those of the full-scale, 2 m diameter commercial turbine from Wing Power Energy. Furthermore, experimental results are presented when varying the model solidity by changing the number of blades, showcasing the effects on turbine performance as a function of these aerodynamic quantities. [Preview Abstract] |
Tuesday, November 26, 2019 9:29AM - 9:42AM |
Q14.00009: Effect of helical-shape blades on the wake flow characteristics of vertical axis wind turbines. Shuolin Xiao, Rongnan Yao, Daniel Araya, John Dabiri, Di Yang Vertical axis wind turbine (VAWT) is a widely used type of wind energy harvesting device. In recent years, considerable efforts have been devoted to studying the turbulent wake flow characteristics behind VAWTs. While most previous studies have focused on the VAWTs with straight blades, limited progress has been made for understanding the wake flow dynamics of VAWTs with helical-shape blades. In this study, the characteristics of turbulent wake flows behind helical-shape VAWTs are investigated both by wind tunnel experiments using the particle image velocimetry (PIV) technique and by large-eddy simulation (LES) using the actuator-line model (ALM). This talk presents the preliminary PIV and LES-ALM results for the wake behind a helical-shape VAWT and compares them to those for a straight-blade VAWT. [Preview Abstract] |
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