Simulation of flow phenomena at the helicopter rotor with high accuracy

该项目的总体目标是提高直升机的气动和气动声学模拟能力。高级数值——在这个例子中是高阶的不连续伽辽金离散——已经在更简单的一般问题中被证明是成功的，现在的目标是将它们的价值与现有的flow求解器（如FLOWer）的可能性结合起来。因此，新一代技术先进的仿真工具将会出现。考虑到当前和未来计算技术的具体特点，我们希望建立新的精度、可靠性和效率水平。因此，可以预期的是，直升机飞行包线中额外的和更有问题的部分，如高负荷或侧向飞行，甚至尾翼震动条件，都可以成功地模拟出来，因此“虚拟首次飞行”的愿景比以往任何时候都更接近。在项目的前一部分，新的DES（分离涡流模拟）模型已经成功实施和验证。此外，现有的DG流求解器的运行时间已经减少了近一个数量级，同时保持甚至提高了并行效率，最多可达数千个处理器。在目前提出的项目中，这些努力将继续朝着直升机旋翼复杂流动现象的模拟方向发展。为了达到这一目标，必须扩展物理模型及其公式，以涵盖动态失速的高度不稳定流动特征，动态失速发生在后退叶片的前飞中，并且可能对整个流场产生重大影响。另一方面，不可避免地要处理旋翼叶片的弹性问题，旋翼叶片的变形会对空气动力学产生反作用。因此，必须考虑网格的运动和变形，并利用重叠网格的嵌合体技术交换网格之间的流动状态。虽然湍流模型以及网格变形和奇美拉转移是一种成熟的技术，但它们在高阶离散中的使用必须非常密切地观察，并且可能会出现一些适当的修改。最后，我们的精度改进不仅要在推力和功率消耗等全局值上进行评估，而且要在遇到BVI（叶片涡相互作用）事件的下降飞行的声学后处理中进行评估。总而言之，这些新颖的工具将有助于可靠地、足够准确地回答具有挑战性的技术问题，以便在中期显著扩展现有方法的能力。

The global goal of the project is the improvement of aerodynamic and aeroacoustic simulation capabilities for the helicopter. Advanced numerics - in this case Discontinuous Galerkin discretisations of high order - have already proven successful in simpler generic problems, and the aim is now to bring their value together with the existing possibilities of established flow solver like FLOWer. In consequence, a new generation of technologically advanced simulation tools will emerge. Taking into account the specific features of current and future computing technology we want to establish new levels of accuracy, reliability and efficiency. Therefore it is to be expected, that additional and more problematic parts of the helicopter flight envelope like highly loaded or sideward flight or even tail shake conditions can be simulated successfully and so the vision of a "virtual first flight" comes closer than ever.In a previous part of the project new DES (Detached Eddy Simulation) models have been successfully implemented and validated. Furthermore, run times of the then existing DG flow solver have been reduced by nearly an order of magnitude, while maintaining and even improving parallel efficiency up to thousands of processors. In the currently proposed project these efforts shall be continued towards the simulation of the complex flow phenomena at the helicopter rotor.In order to reach that goal, the physical model and its formulation have to be extended to cover the highly instationary flow features of dynamic stall, which happens in forward flight at the retreating blade and may significantly influence the entire flow field. On the other hand, it is inevitable to handle the elasticity of the rotor blades, where their deformation retroacts on the aerodynamics. Therefore the movement and deformation of the meshes have to be considered and - using the Chimera technology of overlapping grids - the flow state between them exchanged. Although turbulence models in general as well as grid deformation and Chimera transfers are well established technology, their usage in high order discretisations has to be observed very closely and possibly some modifications may turn up as appropriate. Finally, the success of our accuracy improvements is to be evaluated not only in global values as thrust and power consumption, but also in the acoustic post processing of descent flight encountering BVI (blade vortex interaction) events.To sum it up, such novel tools shall help to answer challenging technical questions dependably with sufficient accuracy, in order to significantly extend the capabilities of established methods in the medium term.