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Modelling and Simulation of helicopters and tilt-rotors in Vortex Ring State

涡环状态下直升机和倾转旋翼机的建模与仿真

基本信息

批准号：
1804616
负责人：
金额：
--
依托单位：
University of Glasgow
依托单位国家：
英国
项目类别：
Studentship
财政年份：
2016
资助国家：
英国
起止时间：
2016 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=studentship-1804616
关键词：
Modelling Simulation helicopters tilt rotors

项目摘要

Progress with computational fluid dynamics based on the Navier-Stokes equations allows for the computation of flows around propellers within realistic time-scales. The most established method for such simulations is to employ the Unsteady Reynolds-Averaged Navier-Stokes method that is a good compromise between accuracy and efficiency. This is because URANS doesn't need to resolve all flow scales which leads to CFD meshes of the size of millions of cells and time steps that are of 1/100 of the chord travel-time of particles. The results can be used for the computation of the mean pressure and velocity fields as well as the slowest frequencies present in the flow. When translated to acoustics, the method can only give tone-noise while the broadband spectrum remains under-resolved.In terms of geometric complexity, the use of structured or unstructured grids is possible, and by employing overset or sliding meshes, the predictions can account for the interaction between the wing and nacelle of an installed propeller system. The Helicopter Multi-Block method of Glasgow has all the ingredients for computing the flow around installed propellers based on the URANS approach and it is therefore a good starting point for research work in this area. On the other hand, the need to resolve more and more harmonics as well as the broad-band part of the acoustic spectrum present in propeller flows, requires more sophisticated techniques that are based on simulation rather than modelling of turbulence. Glasgow has substantial experience with Detached Eddy Simulation for the computation of flows inside weapon bays and helicopter rotors. DES could, in principle, be used for propellers and should allow for the resolution of a large part of the flow spectrum at the expense of more computational resources. For a flow around a propeller blade, grids of the order of 10 million cells should be used with this method and time steps of the order of 1/10000 of the chord travel-time. This of course leads to an increase of the required CPU time by a factor of 100 in comparison to URANS (due to the use of efficient time-integration schemes in the HMB solver). To avoid the penalty associated with this method. The recently-developed Structure-Adaptive-Simulation or SAS should be tested for propeller flows. This method should give results close to the DES at almost twice the cost of the URANS method. It is therefore advisable to adopt a triple strategy that begins with the evaluation of the URANS and DES for propeller flows and then compare the potential gains of SAS with the promised reduction in CPU time in comparison to the DES method. The CFD results of any of the above method can be combined with a number of tools for the further exploitation of the pressure field in conjunction with far-field aeroacoustics methods.Glasgow has experience with the FW-H method that is popular in the field of helicopter rotors. The method uses the CFD-generated unsteady pressure and based on the linearized acoustics equations, produces the acoustic signature of the propeller at distances far apart from the source of noise.Thickness, loading and broadband noise sources could be resolved in the near-field and propagated further of the CFD domain with the FWH method. In addition, trailing edge noise should be resolved by a fine-mesh DES solution.A second method that could be combined with the CFD results could lead to the prediction of the noise-level inside the cabin of an aircraft equipped with propellers. This would lead to an integrated simulation environment where the propeller performance and its acoustics could be studied and used for the far-field and cabin noise predictions at the same time.

基于Navier-Stokes方程的计算流体动力学的进展允许在现实的时间尺度内计算螺旋桨周围的流动。这种模拟的最成熟的方法是采用非定常雷诺平均纳维尔-斯托克斯方法，这是准确性和效率之间的一个很好的折衷。这是因为URANS不需要解决所有的流尺度，这导致了数百万个单元格的CFD网格和粒子弦旅行时间的1/100的时间步长。结果可用于计算平均压力和速度场以及最慢的频率在流动中存在。当转换到声学时，该方法只能给出音调噪声，而宽带频谱仍然是欠分辨的。在几何复杂性方面，可以使用结构化或非结构化网格，并通过采用重叠或滑动网格，预测可以考虑安装的螺旋桨系统的机翼和短舱之间的相互作用。格拉斯哥的“直升机多块”方法具有根据URANS方法计算已安装螺旋桨周围气流的所有要素，因此，它是该领域研究工作的一个良好起点。另一方面，需要解决越来越多的谐波以及螺旋桨流中存在的声学频谱的宽带部分，需要基于模拟而不是湍流建模的更复杂的技术。格拉斯哥在计算武器舱和直升机旋翼内的流动方面具有大量的分离涡模拟经验。DES原则上可用于螺旋桨，并应允许以更多的计算资源为代价来解决大部分流谱。对于螺旋桨叶片的绕流，这种方法应使用1000万个网格的数量级，时间步长为弦线走时的1/10000。这当然导致所需的CPU时间与URANS相比增加了100倍（由于在HMB求解器中使用了有效的时间积分方案）。以避免与这种方法相关的惩罚。最近开发的结构自适应模拟或SAS应测试螺旋桨流。这种方法应该得到接近DES的结果，而成本几乎是URANS方法的两倍。因此，建议采用一种三重策略，首先评估螺旋桨流的URANS和DES，然后将SAS的潜在收益与DES方法相比所承诺的CPU时间减少进行比较。上述任何一种方法的计算流体动力学结果都可以与许多工具结合起来，以便进一步利用远场气动声学方法来研究压力场。格拉斯哥对直升机旋翼领域中流行的FW-H方法有经验。该方法利用CFD产生的非定常压力，基于线性化的声学方程，在远离噪声源的距离处产生螺旋桨的声学特征，利用FWH方法可以在近场求解厚度、载荷和宽带噪声源，并将其传播到CFD域。此外，尾缘噪声应采用细网格DES解来求解。第二种方法可与CFD结果相结合，用于预测装有螺旋桨的飞机机舱内的噪声级。这将导致一个集成的仿真环境，螺旋桨的性能和它的声学可以研究，并用于远场和机舱噪声预测在同一时间。