Numerical flow analysis of vertical axis wind turbines with morphing airfoils

变形翼型具有改变其几何形状的能力，以优化特定操作流动条件下的气动力。这项技术在应用于垂直轴风力涡轮机(VAWT)时非常有效，因为这些涡轮机的叶片在旋转时会遇到不同的攻角。为了同样的目的，变桨距技术在过去也曾被研究过，但它在机械上更难实现，而且提供的灵活性比变形翼型要小。变形形状的控制更容易实现，并具有更大的潜力来优化每个叶片产生的瞬时扭矩。拟议的研究将研究变形翼型，它会改变后缘的几何形状，从而改变翼型的弯曲线。改变几何形状可以用来防止动态失速，增加旋转背风部分的功率提取，在旋转周期内分配负载，或作为断开系统。这项研究计划提出了一种方法来了解变形几何体的影响，特别是在动态失速期间。它还包括开发一个计算工具，用于预测VAWT在不同变形策略下提取的功率。计算流体动力学技术是模拟复杂几何形状周围流体流动的强大工具。虽然计算成本较高，但大涡模拟(LES)是研究动态失速等复杂非定常流动的必要模型。多年来，Paraschivoiu教授的研究小组开发了内部LES-CFD程序，并对VAWT进行了验证。本方案的目标是进一步开发数值算法和软件，并利用这些算法和软件来分析变形叶片上的流动以及动态失速。这项研究的其他重要方面将是对改进的大涡模拟模型的研究，以及增加新的加速技术，这些技术将减少大涡模拟通常所需的大量计算时间。

A morphing airfoil has the ability to change its geometry in order to optimize the aerodynamic forces for a specific operating flow condition. This technology can be very effective when applied to vertical axis wind turbines (VAWTs), because the blades of these turbines encounter different angles of attack as they rotate. Variable pitch technology has been investigated in the past for the same purpose, but it is mechanically more difficult to implement and offers less flexibility than morphing airfoils. Control of the morphing shape is easier to implement and has a greater potential for optimizing the instantaneous torque generated by each blade. The proposed research will investigate morphing airfoils that change the geometry of the trailing edge, and therefore the camber line of the airfoil. Changing the geometry can be used to prevent dynamic stall, to increase power extraction in the leeward portion of the rotation, to distribute the load over the rotation cycle or as a breaking system. This research plan proposes an approach to understand the influence of morphing the geometry, in particular during dynamics stall. It also includes the development of a computational tool for predicting the power extracted by a VAWT for different morphing strategies.Computational Fluid Dynamics techniques are powerful tools to simulate fluid flow around complex geometries. Although computationally expensive, Large Eddy Simulation (LES) is a necessary model to study complex unsteady flows such as the one occurring during dynamic stall. Over the years, an in-house LES-CFD code has been developed by Prof. Paraschivoiu's research group, and validated for VAWTs. The objective of the current proposal is the further development of the numerical algorithms and software, and to use these to analyze flow over morphing wind turbine blades, as well as dynamic stall. Other important aspects of the research will be the investigation of an improved LES model and addition of new acceleration techniques that will reduce the significant computation time that LES typically requires.