Studies on Vertical Axis Wind Turbines Technologies

将单独研究Darrieus型垂直轴风力涡轮机(VAWT)的气动弹性和气动声学行为，并在风力发电场编队中进行。达里厄斯风力涡轮机在20世纪70年代的S时代很常见，但由于振动过大的问题而被淘汰。“智能”控制系统和叶片节距控制抑制振动的进步，以及复合材料叶片结构的出现，使这一概念设计如今重新焕发生机。此外，有必要在更深的水域建设海上风力发电场，以将人口稠密地区附近不可避免的视觉和噪音污染降至最低，这促使该行业考虑使用浮动风力涡轮机。由于其固有的稳定性问题，水平轴风力机不适合浮式安装。在HAWT中，由于重型发电机的作用，涡轮机的重心被向上推。在浮式装置中，重心需要靠近水面，以保证水轮机的浮动稳定性。VAWT适用于这种情况，因为VAWT发电机可以位于涡轮机的底部。“troposkien”(源自希腊语“旋转绳”)几何学通常被用来设计Darrieus VAWT。“troposkien”是链条以一定的速度旋转时所呈现的形状。在这种情况下，没有弯矩，而张力是结构中唯一存在的内力。因此，“对流层”形状最大限度地减少了达里厄斯几何体的疲劳问题。考虑叶片结构曲率的非线性效应和叶片方位角区存在的气动失速，研究了在非定常空气动力作用下“对流层”曲梁的结构动力行为。结构动力学将以状态向量混合形式表示，其中面内和面外方向的力和位移都将被视为因变量。VAWT的气动模拟将结合自由尾迹涡模型，其中每个叶片部分将由于叶片升力随时间的变化而脱落涡流。在拉格朗日描述的流动中，由相邻涡旋的涡度和自由风速引起的速度场将使脱落的涡流(细丝或颗粒)在空间中演化。为了更好地描述流动，将包括塔(钝体)效果。这种数值方法在计算上有效地表示了旋翼中的自由尾迹，因为它是无混浊的，并且对于传统的(基于网格的)计算流体力学方法中通常遇到的涡强的不切实际的数值耗散具有很强的稳健性。将上述结构模型和气动模型耦合起来，对结构在非定常动力和气动载荷作用下的自激(颤振和极限环振动)和气动弹性强迫响应进行了数值研究。叶片上的非定常声压产生的气体声发射也将从叶片的局部升力中确定，以估计涡轮机的噪声足迹，并与使用应变计的定标涡轮机风洞测试的实验数据进行比较。该项目的最终目标将是开发“智能”控制系统，以最大限度地减少早期安装的Darrieur转子所检测到的高振动问题，并增强其在风力发电场安装中的性能(即能量提取)，其中一个涡轮机的自由尾迹受到其他涡轮机的影响。

The aeroelastic and aero-acoustic behaviour of Darrieus-type vertical axis wind turbines (VAWT) individually and in wind farm formations will be investigated. Darrieus wind turbines were common in the 1970's but they were phase out due to problems with excessive vibrations. Advances in "smart" control systems and blade pitch control to suppress vibrations and the advent of composite blade structures have revitalized this conceptual design nowadays. In addition, the necessity of building offshore wind farms in deeper water to minimize the unavoidable visual and noise pollution near populated areas have pushed the industry to consider floating wind turbines. Horizontal axis wind turbines are not appropriate to floating installations due to its inherent stability problems. In HAWT the centre of gravity of the turbine is pushed upwards due to the heavy electric generator. In floating installations, the centre of gravity needs to be close to the surface of the water to guarantee the floating stability of the turbine. VAWT are appropriate in this case because VAWT generators can be located at the base of the turbine. The "troposkien" (from the Greek "rotating rope") geometry has been usually invoked to design Darrieus VAWT. The "troposkien" is the shape that a chain takes when it is rotating at a certain rate. In this situation, the bending moment is absent and the tension is the only internal force present in the structure. Therefore, the "troposkien" shape minimizes the fatigue problems of the Darrieus geometry. The structural dynamic behavior of a curved beam shaped in the "troposkien" under the action of the unsteady aerodynamics will be investigated considering the non-linear effects due to both the structural curvature of the blade and the aerodynamic dynamic stall present in regions of the blade azimuth angle. The structural dynamics will be expressed in a state-vector mixed formulation form where both forces and displacements in the in- and out-plane directions will be considered as the dependent variables. The aerodynamic simulation of the VAWT will be developed incorporating a free-wake vortex model where each blade section will shed vortices due to the changes in the blade lift over time. The shed vortices (filaments or alternatively particles) will be let to evolve over space in a Lagrangian description of the flow by the velocity field induced by both the vorticity of the neighbouring vortices and the wind free speed. Tower (blunt-body) effects will be included for a better description of the flow. This numerical approach is computationally efficient to represent the free-wake in rotating wings as it is mash-less and so robust to unrealistic numerical dissipation of the vortex strength normally encountered in traditional (grid-based) computational fluid dynamics methods. Coupling the aforementioned models for the structure and the aerodynamics both the self-excited (flutter and limit cycle oscillations) and the aeroelastic forced response of the structure due to the unsteady dynamic and aerodynamic loading will be investigated numerically. Aero-acoustic emissions generated by the unsteady acoustic pressure on the blades will also be determined from the blade local lift to estimate the turbine noise footprint and compared with experimental data from wind tunnel tests with a scaled turbine instrumented with strain gauges. The final objective of the project will be to develop "smart" control systems to minimize the high vibration problems detected with earlier installations of the Darrieurs rotor and to enhance its performance (i.e. energy extraction) in wind farm installations where the free-wake of one turbine is affected by the presence of others.