Endwall Flow Mechanisms in Electric Propulsors

在过去的几十年里，航空业及其排放的急剧增长引起了人们对航空电气化的兴趣。电池和发动机技术限制了电动飞机的可能航程，使其仅适用于城市环境中的短期任务。由于这些环境中的基础设施限制，这些飞机中的大多数都是为垂直起降（e-VTOL）而设计的。轴驱动涵道风扇通常用于推进e-VTOL，从而实现安全和安静的任务。然而，最近的研究项目表明，将电动机放置在转子的护罩（边缘驱动风扇，RDF）可以提高推进器的性能。轮缘提供了对机械应力的支撑，并且电机冷却和布线变得不那么复杂，因为电缆不穿过气路。然而，旋转的护罩会改变流场并影响系统的效率。从现有文献中可以清楚地看出，转子尖端区域的流型（称为端壁流）会影响涵道风扇的气动损失和稳定性。已经完成的大部分工作都集中在传统的悬臂式转子叶片上，不适用于RDF。因此，本博士项目旨在分析护罩对气动性能的影响，包括效率和失速裕度，并评估e-VTOL不同风扇设计之间的权衡。将进行定常和非定常CFD模拟，以研究整个e-VTOL飞行使命中发动机内的流场。这种设计的非定常模拟在以前的研究中没有进行过，并且对于理解在发动机的某些操作条件下出现的流动不稳定性的原因和后果是必要的。所研究的设计将在惠特尔实验室的e-VTOL专用钻机中快速制造和测试。为了评估RDF的可行性，将采用综合系统方法，考虑新设计对所有发动机部件的影响。

Over the last decades, the dramatic growth of the aviation industry and its emissions has caused an increased interest in the electrification of aviation. The battery and motor technology limit the possible range of electric aircraft, making them suitable only for short missions in urban environments. Due to the infrastructure limitations in these environments, most of these aircraft are designed for vertical take-off and landing (e-VTOLs). Shaft-driven ducted fans are commonly used for the propulsion of e-VTOLs leading to safe and quiet missions. However, recent research projects suggest that placing the electric motor at the rotor's shroud (Rim-Driven Fan, RDF) could enhance the propulsor's performance. The rim provides support against mechanical stresses, and the motor cooling and wiring become less complex as cables do not cross the gas path. Nonetheless, the rotating shroud would modify the flow field and affect the system's efficiency.From the existing literature, it is clear that the flow patterns developed at the tip region of the rotor, referred to as endwall flows, affect the aerodynamic loss and stability of ducted fans. Most of the work already done is focused on conventional, cantilevered rotor blades and does not apply to RDFs. Hence, this PhD project aims to analyse the effect of shroud on the aerodynamic performance, in terms of both efficiency and stall margin, and assess the trade-offs between the different designs of fans for e-VTOLs.Steady and unsteady CFD simulations will be carried out to investigate the flow field developed within the engine throughout the e-VTOL flight mission. Unsteady simulations for such designs have not been conducted in previous studies and are necessary to understand the causes and consequences of flow instabilities appearing under certain operating conditions of the engine. The designs examined will be rapidly manufactured and tested in an e-VTOL dedicated rig in the Whittle laboratory. To assess the feasibility of RDFs an integrated-system approach will be adopted, accounting for the impact of the new design on all the engine components.