Combined aeroacoustic and flow diagnostic analysis of the motion induced sound generation by an oscillating airfoil with active flap

非定常攻角下翼型产生的流致噪声是气动声学领域中一个重要的问题。示例包括桨距控制风力涡轮机的转子叶片和用于流动控制的主动后缘襟翼。通过翼或叶片的运动，产生声音的流动结构的轨迹发生变化，并且这些流动结构与运动的翼相互作用。这使得声源的定位和表征以及声音生成过程的建模都变得复杂。在这里的拟议项目的框架内，流动诊断方法，最近开发的申请人之一，已扩展到应用的气动声学调查的运动机翼。该方法结合了麦克风测量在声学远场与流量测量，并提供了深入了解的空间和时间发展的流动结构，参与声音生成过程。该程序是基于湍流波动和压力波动，辐射声波在声学远场之间的相关系数的计算。通过对所得系数矩阵进行时空分析，可以识别出与气动声学相关的流场结构的轨迹。该项目的新奇在于将这种方法应用于具有可变后缘襟翼的运动机翼周围复杂流动的气动声学现象。机翼的运动对相关系数有很大的影响。尽管有一个明确的解释的相关系数和表征的声音生产，一个详细的分析的特征相干流结构和它们的动态是必要的。本计画的最终目标是为改进动翼气动噪声的预测模型做出贡献。这应包括噪声的空气动力学特性和运动机翼对声音传播的影响。

Flow induced noise generated by wing profiles with unsteady change of the angle of attack is of crucial importance for a variety of open questions in the field of aeroacoustics. Examples include rotor blades of pitch-controlled wind turbines and active trailing edge flaps for flow control. By the movement of the wings or blades, the trajectories of sound producing flow structures vary and these flow structures interact with the moving wing. This complicates both the localization and characterization of the sound source as well as the modelling of the sound generation process. Within the framework of the proposed project here a flow diagnostic methodology, recently developed by one of the applicants, has to be extended to the application for the aeroacoustic investigation of moving wings. The methodology combines microphone measurements in the acoustic far-field with flow measurements and provides insights into the spatial and temporal development of flow structures, being involved in the sound generation process. The procedure is based on the calculation of the correlation coefficient between turbulent fluctuations and pressure fluctuations, which radiate as sound waves in the acoustic far field. The trajectories of aeroacoustic relevant flow structures can be identified by a space-time analysis of the resulting coefficient matrix. The novelty of this project is the application of this methodology to the aeroacoustic phenomenon of complex flows around moving wings with variable trailing edge flap. The correlation coefficients are strongly influenced by the movement of the wing. Despite a clear interpretation of the correlation coefficients and the characterization of sound production, a detailed analysis of the characteristic coherent flow structures and their dynamics is necessary. The ultimate goal of this project is to make a contribution to an improved prediction-model for aerodynamically induced noise of moving wings. This should include both the aerodynamic characterization of the noise and the influenced to the sound propagation by the moving wing.