Non-Intrusive Multidimensional Investigation of Spallation Phenomena in Ablating Materials

本研究是对航天器热防护材料层裂现象的多维实验研究。层裂是烧蚀过程中一个重要但知之甚少的组成部分，它为进入行星大气的航天器提供热保护，确保飞行和任务成功。到目前为止，文献中可获得的实验层裂数据数量非常有限，而且没有特别详细的数据。这项工作的目的是首次整理针对层裂的广泛实验测量结果，并量化层裂对航天器热载荷的影响。这分为两部分，首先将表征材料的表面状态和从表面喷出的层裂颗粒，其次将评估这些颗粒对整体流场的影响。将使用双色比热法、摄影测量、层析成像和高速成像对表面状态进行详细的调查。这将导致测量散裂的颗粒数量以及颗粒大小、温度和速度。表面状态测量对于理解材料的响应是至关重要的，因为这很大程度上受表面温度和表面物理剥离材料的量的影响。这些测量将允许评估散裂过程对整体烧蚀和材料响应的影响。此外，抛射粒子的特性是模拟散裂粒子对流场影响的关键。这项研究的第二部分是通过实验确定散落粒子对整个流场的影响。粒子通过散裂过程被抛出，并将新的辐射和反应成分引入到流场中，这些成分在烧蚀模拟中历来被忽略。利用光谱学、高速过滤成像和层析成像技术，这项研究将量化这些注入颗粒对流场的影响。这些实验将从绝对辐射强度和辐射的空间分布两个方面测量粒子引起的辐射强度变化。这次研究产生的数据集将是对层裂现象的第一次广泛和详细的测量。这些数据可用于材料响应代码的验证和验证以及烧蚀流场耦合计算分析。这可以改进航天器热防护材料的数值模型，确保未来航天器热防护设计的更高确定性和效率。

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.