LowNoise: Linear Stability and Resolvent Analysis for Prediction and Mitigation of Wind Turbine Trailing-edge Noise

低噪声：用于预测和缓解风力涡轮机后沿噪声的线性稳定性和分辨率分析

• 批准号: 458062719
• 负责人: Professor Dr.-Ing. Kilian Oberleithner
• 金额: --
• 依托单位: Instituto Tecnológico de Aeronáutica (ITA)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/458062719?language=en
• 关键词: LowNoise; Linear; Stability; Resolvent; Analysis

The mitigation of flow noise from wind turbines is of central importance for current and future, even more powerful wind turbines. The most important noise source is the trailing-edge noise. It is caused by pressure fluctuations in the boundary layer at the trailing edge of the rotor blade. Frequency characteristics and sound levels depend largely on the coherent eddy-like structures in the boundary layer. Current methods to reduce trailing-edge noise show contradictory results, as their influence on the coherent structures is neither sufficiently understood nor reliably modelled.Current investigations on free shear flows and boundary layer flows clearly show that linear stability and resolvent analysis can be used to systematically describe the formation and control of coherent structures. Therefore, in the LowNoise project, these very successful and novel methods are applied to the flow field of a typical wind turbine airfoil. The central goal is a physical low-dimensional model which describes the essential mechanisms of trailing-edge noise.The modelling is done in several steps. The coherent structures are approximated as linear modes of the mean-flow field, which can be determined by the stability or resolvent analysis. The pressure fluctuations on the wing surface are then determined by data assimilation from the linear modes. The trailing-edge noise, then, results from the integral of the pressure field on the wing surface.The central innovation of this approach is the modelling of the sound sources using linear stability and resolvent theory. On the one hand, this enables the quantitative determination of the trailing-edge noise at significantly fewer empirical input variables than with current low-dimensional models. On the other hand, the model provides the causal mechanisms of the formation of the coherent structures, and thus, of the trailing-edge noise, which allows to optimise existing control measures and to develop new more effective control measures.The LowNoise project starts with large-eddy simulations of the entire flow field. From the flow fields the velocity and pressure fluctuations of the coherent structures can be extracted and an empirical low-dimensional model can be derived. Based on the mean-flow fields of the simulation the stability and resolvent theory model will be developed. The validation of the simulations and the model is done experimentally by means of pressure and acoustic measurements in a wind tunnel. The project ends with a model-based analysis of the control influences of the trailing-edge noise.The models developed in LowNoise will show the essential physical relationships for the generation and effective reduction of trailing-edge noise of wind turbines. Furthermore, the model and concepts developed in LowNoise can be applied to a variety of other wall-bounded flows.

降低风力涡轮机的流动噪声对于当前和未来，甚至是更强大的风力涡轮机来说都是至关重要的。最重要的噪声源是后缘噪声。这是由转子叶片后缘边界层的压力波动引起的。频率特性和声级在很大程度上取决于边界层中的相干涡状结构。现有的抑制尾缘噪声的方法对相干结构的影响没有得到充分的理解，也没有得到可靠的模拟，目前对自由剪切流和边界层流动的研究表明，线性稳定性和预解分析可以系统地描述相干结构的形成和控制。因此，在LowNoise项目中，这些非常成功和新颖的方法被应用到典型的风力机翼型的流场中。中心目标是描述后缘噪声的基本机制的物理低维模型。建模分几个步骤完成。相干结构被近似为平均流场的线性模式，可以通过稳定性分析或预解分析来确定。然后，通过对线性模式的数据同化来确定机翼表面的压力波动。这种方法的主要创新之处在于利用线性稳定性理论和预解理论对声源进行建模。一方面，这使得能够在比目前的低维模型少得多的经验输入变量下定量确定后缘噪声。另一方面，该模型提供了相干结构和后缘噪声形成的原因机制，从而允许优化现有的控制措施和开发新的更有效的控制措施。LowNoise项目从整个流场的大涡模拟开始。从流场中可以提取出拟序结构的速度和压力脉动，并可以得到经验的低维模型。基于模拟得到的平均流场，建立了稳定性和预解性理论模型。通过风洞中的压力测量和声学测量对模拟和模型进行了实验验证。项目最后对尾缘噪声的控制影响进行了基于模型的分析。在LowNoise中开发的模型将显示产生和有效降低风力涡轮机尾缘噪声的基本物理关系。此外，在LowNoise中开发的模型和概念可以应用于各种其他壁面边界流。