Turbulent flow field and resulting noise induced by hub-less propellers

船舶推进系统产生的水下噪声已成为当今日益突出的环境问题。一个新的有前途的设计概念，以减少发出的水下噪音是使用无轴螺旋桨与电环驱动。关于这种新型推进系统的详细研究，特别是关于无轮毂螺旋桨内部和后部的湍流流场以及由此产生的声场，迄今尚未开展。本项目主要研究尾流的整体拓扑结构、叶尖涡的过渡和崩塌、叶片轮毂马蹄形涡的拓扑结构和辐射水声声场。无轮毂螺旋桨尾流的时间分辨立体PIV实验和脉动表面压力的时间同步测量以及湍流流场的全瞬态DES计算将是计划研究工作的核心内容。在有限体积公式的基础上，提出了一种四阶不可压缩流展开式水声压力场的数值预测方法。对实验数据、数值数据的分析和对相干流结构的识别将采用适当的正交分解方法。此外，还将与涡核提取方法相辅相成。由于POD方法的使用，将首次有可能对不同相干流结构的声学特性进行总结。在本工程的展望中，可以推导出减少水声声发射的第一设计规则。

The underwater noise which is generated by ship propulsion systems becomes a more and more growing environmental problem nowadays. A new promising design concept for the reduction of emitted underwater noise is the usage of hub-less propellers in conjunction with an electrical ring drive. Detailed research with respect to this new propulsion system, especially in terms of the turbulent flow field in and behind a hub-less propeller and the resulting sound field, has not been carried out so far. Main focus of the proposed project will be the investigation of the overall topology of the wake flow, the transition and collapse of the tip vortices, the topology of the horseshoe vortices at the blade hub and the radiated hydro acoustic sound field. Time resolved stereo PIV experiments in the wake flow of a hub-less propellers and time synchronous measurements of the fluctuating surface pressure in combination with fully transient DES computations of the turbulent flow field will be core elements of the planned research work.For the numerical prediction of the hydro-acoustic pressure field a fourth order Expansion over Incompressible Flow (EIF) approach will be developed based on a finite volume formulation. The approach for the analysis of the experimental data, numerical data and for the identification of coherent flow structures will be the Proper Orthogonal Decomposition procedure (POD). Moreover it will be complemented with vortex core extraction methods. Due to the usage of the POD method, conclusions to the acoustics of different coherent flow structures will be possible for the first time. In the outlook of this project, first design rules for the reduction of hydro-acoustic sound emissions might be reasoned.