Non-Intrusive Multidimensional Investigation of Spallation Phenomena in Ablating Materials

本文对航天器热防护材料的散裂现象进行了多维度的实验研究。溅落是烧蚀过程中一个重要的但鲜为人知的组成部分，它为进入行星大气层的航天器提供热保护，确保飞行和任务的成功。到目前为止，文献中只有非常有限的实验碎裂数据，并且可用的数据不是特别详细。这项工作的目的是第一次整理针对碎裂的广泛实验测量结果，并量化碎裂对航天器热载荷的影响。这分为两个部分，首先，材料的表面状态和从表面喷射出的散裂颗粒将被表征，其次，这些颗粒对整个流场的影响将被评估。对表面状态的详细研究将使用双色比热法、摄影测量法、断层扫描和高速成像进行。这将导致颗粒碎裂的数量和颗粒的大小，温度和速度的测量。表面状态测量对于理解材料响应至关重要，因为这受到表面温度和从表面物理剥离的材料量的严重影响。这些测量将允许剥落过程对整体烧蚀和材料响应的影响进行评估。此外，抛射颗粒的特性是模拟抛射颗粒对流场影响的关键。本研究的第二个组成部分是实验确定碎裂颗粒对整个流场的影响。颗粒通过散裂过程喷射出来，并在流场中引入了新的辐射和反应成分，这些成分在烧蚀模型中一直被忽略。利用光谱学、高速滤波成像和断层扫描技术，本研究将量化这些注入颗粒对流场的影响。实验将测量由粒子引起的辐射强度变化，包括绝对辐射强度和辐射的空间分布。从这次调查中得到的数据集将是对散裂现象的第一次广泛和详细的测量。这些数据可用于验证和验证材料响应代码和耦合烧蚀流场计算分析。从而可以改进航天器热防护材料的数值模型，为未来航天器热防护设计提供更高的确定性和效率。

This study is a multidimensional experimental investigation into the spallation phenomena for spacecraft thermal protection materials. Spallation is an important, yet poorly understood, component of the ablation process which provides thermal protection for a spacecraft entering a planetary atmosphere ensuring flight and mission success. Thus far there is only a very limited amount of experimental spallation data available in the literature, and the data which is available is not particularly detailed.The objective of this work is to, for the first time, collate extensive experimental measurements targetting spallation and to quantify the effects of spallation on spacecraft thermal loading. This is split into two components, firstly the surface state of the material and the spallation particles ejected from the surface will be characterised, and secondly, the effect of these particles on the overall flow field will be evaluated.A detailed investigation of the surface state will be conducted using two-colour ratio pyrometry, photogrammetry, tomography and high-speed imaging. This will result in the measurement of the number of particles spallated and the particle sizes, temperatures and velocities. The surface state measurements are critical for understanding the material response as this is heavily influenced by the surface temperature and the amount of material physically stripped from the surface. These measurements will allow the effect of the spallation process on the overall ablation and material response to be evaluated. Additionally, the ejected particle characteristics are key to the modelling of the effect of the spalled particles on the flow-field.The second component of this investigation is the experimental determination of the effect of the spalled particles on the overall flow-field. The particles are ejected by the spallation process and introduce new radiating and reacting components into the flow-field which have been historically ignored in ablation modelling. Utilising spectroscopy, high-speed filtered imaging and tomography this investigation will quantify the effect of these injected particles on the flow-field. The experiments will measure the radiation intensity modifications caused by the particles, both in terms of absolute radiation intensity and spatial distribution of the radiation.The data sets resulting from this investigation will be the first extensive and detailed measurements of the spallation phenomena. These data can then be used for verification and validation of material response codes and coupled ablation flow-field computational analyses. This can then improve the numerical models of spacecraft thermal protection materials ensuring higher certainty and efficiency in future spacecraft thermal heat shield design.