Composite structural housing with integrated thermal management

随着现代旋翼机设计从传统动力转向更多的电气系统，对高效热调节的需求从未如此高过。目前的旋翼机系统可以解决这个问题，但它们将受益于更高的集成和优化。实现这一目标的关键可能在于进一步利用在航空航天工业中已经很常见的材料；复合材料。复合材料，即碳和玻璃纤维增强复合材料（CFRPs/GFRPs）在现代飞机上有广泛的应用，可以包含多达40-50%的结构部件。复合材料的流行主要是由于其高强重比和刚度裁剪能力。然而，由于它们的热性能差，它们在温度临界区域受到限制。这意味着它们通常不适用于需要大量散热的部件周围的结构应用。然而，如果这些复合材料的热性能可以在不影响材料本身的机械性能的情况下得到改善，那么好处将是很多的。该项目旨在研究改善复合材料热特性的方法，以帮助从温度关键部件中去除热量。目前有一些新颖的概念可以在小范围内做到这一点，但目前对该领域的文献和研究很少。这可能意味着必须使用一种新技术，或者多种技术的组合来实现这一点。可以使用两种类型的技术；被动和主动冷却。被动冷却系统将利用微观结构或几何特征，并利用周围环境来促进散热，而不需要消耗能量。在微观结构上，这可能包括在复合基体中加入导热添加剂或改善基体内的结晶度。从几何上讲，这可能涉及利用周围条件和转子产生的空速的通风特征。然而，最有希望的概念可能是使用z形钉钉进行簇缝（拼接），以提高复合材料通过厚度方向的导热性。这将在结构中创造更多导电材料（如碳或金属）的导热路径。从机械性能的角度来看，这两种技术已经有了用途，但它们的热效应尚未在研究中进行调查。作为该项目的一部分，已经进行了初步实验来研究z形钉销，并取得了有希望的初步结果。主动冷却系统需要消耗一些能量，以便从系统中除去热量。要做到这一点，最简单的方法是在结构的表面注入冷却液。现代旋翼机中也存在一些类似的系统，但集成到复合结构中非常复杂。然而，可以在复合材料中嵌入通道，形成一个“血管网络”，通过该网络可以泵送冷却剂。基于有限的文献，该技术提供了实现所需冷却效果的最大潜力，并将构成本项目实验工作的主体。通道的尺寸、结构和制造方法，以及冷却剂和流速的选择，都是需要进一步研究的因素。这些变量将为研究创造一个强有力的起点。在确定具有最大潜力的概念之前，该项目将采用双管齐下的方法对被动和主动系统进行实验评估。然后将对这一概念进行更详细的评价，并考虑到具体的应用，以期提高TRL水平并进一步研究未来的项目。

As modern rotorcraft design shifts away from conventional power and towards more electrical systems, the need for efficient thermal regulation has never been higher. Systems are currently in place to combat this in rotorcraft but they would benefit from higher integration and optimisation. The key to achieving this may lie in further utilisation of materials that are already commonplace in the aerospace industry; composites. Composite materials, namely carbon and glass fibre reinforced composites (CFRPs/GFRPs) have widespread applications in modern aircraft and can comprise as much as 40-50% of structural components. The prevalence of composite materials is mainly due to their high strength-weight ratio and stiffness tailoring ability. They are however limited in temperature critical areas due to their poor thermal performance. This means they are generally unsuitable for structural applications around components that require a large amount of heat removal. However, if the thermal performance of these composite materials could be improved without compromising the mechanical properties of the material itself, the benefits would be numerous. This project aims to investigate ways to improve the thermal characteristics of composite materials in ways that would aid the removal of heat from temperature critical components. There are currently a few novel concepts that can do this on a small scale, but current literature and research into the area is scarce. This likely means a new technique, or a combination of techniques would have to be used to achieve this. There are two types of techniques that could be used; passive and active cooling. A passively cooled system would employ microstructural or geometric features and take advantage of the surrounding environment to promote heat dissipation without the need for energy consumption. Microstructurally, this may include thermally conductive additives into the composite matrix or improved crystallinity within the matrix. Geometrically, this may involve ventilation features that take advantage of the surrounding conditions and the airspeed produced by the rotors. Possibly the most promising concept however would be to improve thermal conductivity in the through-thickness direction of the composite using z-pinning for tufting (stitching). This would create thermally conductive pathways within the structure with more conductive materials such as carbon or metals. These two techniques already have uses from a mechanical performance perspective, but their thermal effects have not been investigated in research. Preliminary experiments have already been carried out to investigate z-pinning as part of this project, with promising initial results. An actively cooled system would require some means of energy consumption in order to remove heat from the system. This would most easily be done by pumping a cooling fluid around the surface of the structure. Some similar systems exist in the modern rotorcraft but integration into composite structures is very complex. Channels can however be embedded within the composite to create a 'vascular network' through which coolant can be pumped. Based on the limited literature, this technique offers the most potential to achieve the cooling effect required, and will form the bulk of the experimental work of this project. The size, configuration, and fabrication method of the channels are all factors that need to be investigated further, as well as choice of coolant and flow velocity. These variables will create a strong starting point for research. The project will use a two pronged approach to evaluate both passive and active systems experimentally, before identifying the concept with the highest potential. This concept will then be evaluated in more detail and with a specific application in mind, in the hopes of raising the TRL level and furthering the research for future projects.