1,720,973 research outputs found
2D-3D Computations of a Vertical Axis Wind Turbine Flow Field: Modeling Issues and Physical Interpretations
No full textThis paper presents the results of a numerical investigation on the flow field past a Vertical Axis Wind Turbine at different operating conditions. Several numerical issues are considered, including the extension of the domain, the class of boundary conditions assigned, the space and time resolution, and the numerical accuracy in the resolution of the equations. The inlet boundary condition and the physical position where it is assigned, as well as appropriate far field conditions, are shown to be crucial for the reliability of the computed turbine performance. The use of proper boundary conditions and numerical settings allows performing three-dimensional unsteady calculations of VAWT aerodynamics with a technically-acceptable computational cost. The conclusions obtained are strengthened by a detailed comparison with a large data-base of experiments available for the turbine under consideration, that include both performance and time-resolved velocity measurements in the wake. The resulting flow model is then used to run time-accurate two-dimensional (2D) and three-dimensional (3D) simulations of the flow around the turbine. This set of simulations is exploited in combination to dedicated studies on the unsteady profile aerodynamics as well as detailed three-dimensional measurements in the wake to provide consistent physical interpretations of the computed flow fields
Three-dimensional unsteady aerodynamics of a H-shaped vertical axis wind turbine over the full operating range
No full textVertical-axis wind turbines have great potential for harvesting energy with high conversion efficiency both in small-scale distributed installations and in the emerging floating offshore technology; nevertheless, their complex unsteady flow field makes design and optimization very challenging. This paper documents an extensive CFD study on a H-shaped VAWT over the entire range of operation. First, a direct 2D-3D comparison of the prediction capability of CFD models over the entire turbine operational curve is presented, highlighting the range of operation in which 3D effects become crucial and, instead, the range of TSR for which a 2D approximation is acceptable. The simulations are systematically compared to a wide and accurate experimental data set of wind-tunnel experiments in controlled conditions. The combination of CFD results with measured data allowed to assess the turbine performance and time-resolved velocity measurements in the wake. Furthermore, the paper proposes a totally novel approach in analysing the computed non-periodic unsteadiness in the wake. Finally, a tracking of the unsteady tip vortex is also proposed, with remarkable similarity to experimental results documented in the literature. This fact suggests that URANS discretization permits to approximate the dynamic and evolution of the tip vortex, at least in the near wake region
A Computational Fluid Dynamics Study on the Performance of Modified H-Shaped VAWTs for Tilted Operation Condition
No full textWind energy harvesting may see radical transformation with the introduction of new wind turbine concepts. The vertical axis configuration offers significant advantages that may promote the installation in deep waters, where only floating platforms are feasible and economically convenient. While experimental tests for multi-objective assessment are expensive, and analytical methods relying on blade element momentum are of limited fidelity, advanced, high-fidelity computational fluid dynamics (CFD) techniques are a promising tool for the performance prediction of wind turbines. CFD simulations enable critical evaluation of real-time, long-term aerodynamic loading and prediction across various operational scenarios. This paper presents a fully three-dimensional (3D) CFD investigation on the aerodynamics and near-wake development of a small-scale H-shaped vertical axis wind turbine (VAWT) and two modified versions suited to tilted conditions, typical for spar-buoy applications. An in-depth spanwise study of the three versions at the peak power condition is performed. The difference in the swept area and the coning angle effect in combination with the tilt condition are considered. The obtained results show significant, potential, contribution to the ongoing development of the floating-VAWT technology. The vortical structures development is also commented to provide better understanding of the physical phenomena taking place. Since the relevant energy harvesting capability being predicted for the newly designed turbines, further simulations aimed at demonstrating the engineering relevance of the machines, utility-scale models of the turbine. The numerical predictions confirm the high performance achievable by the HV-shaped wind turbines, providing valuable insights for its future installations
3D CFD study of a DeepWind demonstrator at design, off-design and tilted operating conditions
No full textEnergy transition, towards increased renewables, demands for reliable, efficient, and innovative technical solutions, at acceptable cost. Wind energy conversion exhibits one of the greatest potential, mainly in off-shore deployment. Vertical-axis wind turbines are characterized by a reduced wave recovery and enhanced power output, which boost the installation of bigger capacity turbines, properly cluster to maximize the farm density. These two requirements entail deeper understanding of the wake physics and detailed description of the machine performance. A careful 3D CFD investigation, supported by experimental validation, is carried out to define the relevant flow mechanism of a lab-model, DeepWind demonstrator, in upright and tilted condition. The results show how the performance is varying along the span, and how it is affected by a skewed flow. The lower part of the machine benefits from combined effect of blade curvatures and rotor inclination. A thorough description of the complex vortical field complements the performance data, and provide useful considerations apt for promoting the design of future vertical-axis wind turbines, for floating off-shore applications. The performance parameters are then computed for a full-size rotor to show how the Reynolds effect play a relevant role in the machine aerodynamics of bigger capacity turbines
Three-dimensional CFD simulation and experimental assessment of the performance of a H-shape vertical axis wind turbine at design and off-design conditions
Full text linkThe paper presents the results of a computational study on the aerodynamics and the performance of a small-scale Vertical Axis Wind Turbine (VAWT) for distributed micro-generation. The complexity of VAWT aerodynamics, which are inherently unsteady and three-dimensional, makes high-fidelity flow models extremely demanding in terms of computational cost, limiting the analysis to mainly 2D or 2.5D Computational Fluid-Dynamic (CFD) approaches. This paper discusses how a proper setting of the flow model and of the numerical solution opens the way for carrying out fully 3D unsteady CFD simulations of a VAWT with engineering-relevant computational cost. Two operating conditions are considered, covering both peak efficiency condition as well as off-design operation. The fidelity of the numerical predictions is assessed via a systematic comparison with the experimental benchmark data available for this turbine, consisting of both performance and wake measurements carried out in the large-scale wind tunnel of the Politecnico di Milano. The analysis of the flow field on the equatorial plane allows highlighting its time-dependent evolution, with the aim of identifying both the periodic flow structures and the onset of dynamic stall. The 3D computational model allows investigating the aerodynamics of the struts and the evolution of the trailing vorticity at the tip of the blades, eventually resulting in periodic large-scale vortices
SENSITIVITY OF VERTICAL AXIS WIND TURBINES TO ROTOR SHAPE AND BLADE DESIGN: A COMPUTATIONAL INVESTIGATION
Full text linkHigh-order discontinuous Galerkin computation of axisymmetric transonic flows in safety relief valves
No full textA computational study on the performance and wake development of a tilted H-Shaped VAWT rotor
No full textWind energy is expected to play a key role in achieving challenging decarbonization objectives set by the current green energy transition. VAWTs are well-suited for the emerging market of floating offshore wind and hold significant potential to decrease the levelized cost of energy for offshore platforms. However, the flow field around a VAWT rotor is unsteady and three-dimensional due to the interaction between blades and vortical structures. Computational Fluid Dynamics is a crucial tool to study complex flow structures and optimize the machines at a reduced cost. This study presents a comprehensive 3D CFD investigation of the performance and wakes development trends of a straight-blade H-shaped VAWT operating in a tilted condition, a typical configuration for floating offshore installations. The VAWT model is studied at peak power and off-design TSR values. The predictions are analyzed by considering the complex flow field and near-wake development. The study finds that the 3D flow originating from the struts, the finite blade effects, and the tilted operating condition critically impact the machine's performance. The study provides an in-depth analysis of turbine aerodynamics and spanwise variations to investigate the fluid-dynamic phenomena and their implications on energy production
Three-dimensional modeling and investigation of the flow around a troposkein vertical axis wind turbine at different operating conditions
No full textVertical axis wind turbines of troposkein architecture are among the most attractive technologies for harvesting wind energy off-shore. In this paper, a high-fidelity Computational Fluid-Dynamics model of the flow around troposkein rotors is presented, experimentally validated, and applied to analyze the complex aerodynamics of this machine considering both operation and design aspects. At first, a set of two-dimensional simulations of the machine equatorial section was carried out to compare multiple spatial resolutions and three eddy-viscosity turbulence models, including Spalart–Allmaras, k-ω SST, and k-ω SST in low-Reynolds formulation, using as reference wind-tunnel experimental data. Then, the results of fully three-dimensional simulations for peak power and high TSR conditions are discussed, to further assess the models against experiments and to investigate the turbine aerodynamics and its spanwise variability, the flow around and downstream of the rotor, with particular emphasis on the peculiar character of troposkein rotor wake and the related tip vortices. Finally, the paper proposes an analysis about the impact of blade design on the machine aerodynamics, showing that rotors obtained with the simplest and most economic blade bending procedure outperforms configurations obtained by manufacturing the blades with plane airfoil sections along the troposkein curve
Turbine vane film cooling: Heat transfer evaluation using high-order discontinuous Galerkin RANS computations
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