Time- and frequency-domain turbulent flow analysis of wind turbine unsteady aerodynamics

TJ Mechanical engineering and machinery

Gigante, Fabio Antonio ; Thomson, Douglas

University:University of Glasgow

Department:School of Engineering

关键词: CFD, Reynolds-Average Navier-Stokes equations, harmonic balance, horizontal axis wind turbine, vertical axis wind turbine, SST turbulence model.;   

Others  :  http://theses.gla.ac.uk/7253/1/2016gigantephd.pdf

来源: University of Glasgow

【 摘 要 】

The main objective of the research work presented in this thesis is the development of a single aerodynamic CFD code for the analysis of complex turbulent flow unsteady aerodynamics such as those encountered in horizontal and vertical axis wind turbines.The finite volume parallel CFD Optimized Structured multi-block Algorithm (COSA) research code solves the Navier-Stokes equations on structured multi-block grids and models turbulence effects with Menter's shear stress transport turbulence model.The novel algorithmic contribution of this research is the successful development of a Harmonic Balance (HB) solver which can reduce the run-time required to compute nonlinear periodic flow fields with respect to the conventional time-domain (TD) approach.The thesis also presents a semi-implicit integration based on LU factorisation and a successfully LAPACK libraries integration to massively improve the computational efficiency of the integration of the HB RANS equations and the turbulence model of Menter. The main computational results of this research are for two low-speed renewable energy applications. The former application is a turbulent unsteady flow analysis of a vertical axis wind turbine working in a low-speed turbulent regime for a wide range of operating conditions. The test case is first solved using the COSA TD turbulent solver to analyse and discuss in great detail the unsteady aerodynamic phenomena occurring in all regimes of this complex device. During the turbine rotation there is a generation of blade vortex shedding and wakes all around the rotor which interacts with the blades itself on the returning side. The most important features of the investigated devices were captured with CFD. In addition, a series of investigations have been conducted to analyse the effects of computational domain refinement, number of time steps per revolution and distance of the farfield boundary from the rotor centre on prediction accuracy. The solution of the turbulent flow solver is validated by comparing torque and power coefficients with experimental data and numerical solutions obtained with a state-of-the-art time-domain of commercial package regularly used by the industry and the Academia worldwide. A detailed selection of results is presented, dealing with the various investigated issues.Afterwards, the COSA HB turbulent solver is used to solve the problem and compare the HB resolution and speed-ups with the TD results. The main motivation for analysing this problem is to highlight the predictive capabilities and the numerical robustness of the developed turbulent HB flow solver for complex realistic problems with a strong nonlinearity and to shed more light on the complex physics of this renewable energy device.The latter application regards the turbulent unsteady flow analysis of horizontal axis wind turbine blade sections in yawed wind regime. The TD and HB turbulent flow analysis of a 164 m-diameter wind turbine rotor is performed.CFD represents an accurate design tool to get a better understanding of the physical behaviour of the flow field past wind turbine rotors and the importance of accurate design is increased as the machines tend to become larger. A study at 30% and at 85% blade section is carried out, allowing the analysis of the unsteady forces acting on two different blade sections. The aim of these analyses is to assess the computational benefits achievable by using the HB method for a common nonlinear flow problem and also to further demonstrate the predictive capabilities of the developed CFD system.The turbulent HB solutions highlight that is possible to obtain an accurate analysis as its TD counterparts can do. Moreover, the results highlight that the turbulent HB solver can compute the hysteresis force cycles of the turbine blade more than 10 times faster than the TD approach.The purpose of proving the turbulent COSA HB capabilities for studying the flow field of wind turbines rotor has been fully achieved and this research represent one of the first turbulent HB RANS applications to the analysis of periodic horizontal axis wind turbine flows, and the first application to vertical axis wind turbine flows.