Investigation Of Aerodynamic Performance And Wake Configuration Of Horizontal-Axis Wind Turbines

Due to its relatively high computational efficiency and simplicity compared to other methods, the Blade Element Momentum theory (BEM) still used for industrial design horizontal-axis wind turbines (HAWT). Yet various experimental campaigns have demonstrated that BEM-based design codes are not always sufficiently reliable for predicting the aerodynamic load distributions on the wind turbine blades. This is particularly true for stalled and yawed rotor conditions. This method has been extended with a number of empirical corrections not based on physical flow features. As the method can't capture accurately the wake and three dimensional flow influences, the importance of accurate design models does also increase as the turbines become larger. Therefore, the research is today shifting toward a more fundamental approach, aiming at understanding basic aerodynamic mechanisms. The aim of the project is to get a better understanding of the wake behavior and whose effect to the aerodynamic loads and performances of the wind turbines. From these evaluations, it will hopefully be possible to improve the engineering methods and base them to a greater extent on physical features instead of empirical corrections. The investigation contents and the innovations of the paper are list as follows:1,In the sake of provide the groundwork for the investigation, firstly the classical aerodynamic models were reviewed and all the method's apply ranges and specialties were summarized.2,The wake configuration was analyzed with the prescribed wake method in this paper, the induced velocities expression formula and models of the induced velocities and the wake configuration are obtained from the generalized classical vortex of the rotor. The model is built in two steps in order to first evaluate its functionality for the simple case of the ideal rotor, where the wake translates backwards without expansion and then include the expansion as a parameter easily tuned to investigate its effect on the results. The results shown that the model can used for calculate the wake configuration and aerodynamics performance of the wind turbine rotor. The model can be used for analysis and engineering design of wind turbine. But as the prescribed wake method is based on the experiments, there is certain limitation in its application.3,A second-order accurate model has been developed and validated for modeling the unsteady aerodynamics of a wind turbine. The free-vortex wake method consists of the Lagrangian description of the rotor flow field and viscous effects were incorporated using a viscous splitting approach. The wake geometry solution was then integrated with the rotor aerodynamics model in a consistent manner. The analysis was then used to predict the performance and air loads on a wind turbine in the upwind configuration under unyawed and yawed flow conditions. The present work has demonstrated the versatility and robustness of the free-vortex wake method for wind turbine applications.4,The free wake model coupled with the blade model was used to calculate the performances and air loads for the NREL phase VI wind turbine and compared with BEM model. The skewed wake geometry behind the upwind wind turbine was successfully predicted in yawed flow conditions over a range of yaw angles and tip speed ratios and the calculation results was consistent with the experiments. It has been shown that compared with the BEM model the free wake-lifting surface model is more accurately predict the transient wake aerodynamics to obtain accurate estimates of the unsteady air loads and performances.5,According with the NREL Phase VI wind turbine rotor, the model wind turbine and the experimental platform have been designed and processed. Combined with CFD simulation and calculation, the aerodynamics experiments with particle image velocimetry (PIV) for the three-dimensional flow field with different tip speed ratios was carried out. The whole velocity field of a model HAWT is measured with PIV. The formation and development of the three dimensional wake behind the model wind turbine are systematically measured. The results show that during the downstream development of the wake, the track of the wake centre forms a helical curve whose rotation direction is opposite to that of the rotor and there are obviously three dimensional flows in the wake regions. The distribution of the axial velocity behind the HAWT rotor reveals the expansion and decay of the wake. The axial velocity defect decreases with developing of the wake, suggesting slightly contracting of the wake there. The results show that during the downstream development of the wake, the width of the wake will not be expanded after it expands to some extent and the magnitude of vorticity decreases with downstream developing of the wake vortex.