Investigation of non-equilibrium thermochemistry in expanding flows

膨胀流动中的非平衡热化学研究

• 批准号: 2888405
• 金额: --
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2888405
• 关键词: Investigation; non; equilibrium; thermochemistry; expanding

This project falls within the EPSRC: Fluid dynamics and aerodynamicsAt hypersonic velocities, the behaviour of gases manifests non-equilibrium phenomena, representing the most intricate aspect of understanding and predicting hypersonic flows. The major difficulty in modelling these phenomena lies in accounting for the multitude of degrees of freedom involved throughout the flow history, such as the various gas species and their excitation states. Furthermore, the available thermodynamic and chemical data are inadequately characterized, and existing non-equilibrium models remain marked by uncertainties. However, non-equilibrium phenomena hold critical implications for high-speed engineering applications, particularly in the design and safety of atmospheric entry vehicles. In fact, these phenomena significantly affect vehicle aerodynamics, thermal loads, and propulsion-system efficiency. A notable example is the heating experienced by spacecraft upon entry into planetary atmospheres. This heating predominantly arises from the expansion of plasma around the vehicle's outer edge generating radiation from gases in excited states, far from thermodynamic equilibrium.It was generally assumed that afterbody radiation for Earth entry was negligible in comparison to convective heating, as indicated by the minimal readings from Apollo's afterbody radiometers. However, subsequent findings revealed that the radiometers were calibrated for the wrong wavelength [1], casting doubt on the efficacy of the existing two-temperature model for non-equilibrium flows in the wake of vehicles entering Earth's atmosphere. The understanding of non-equilibrium phenomena is even more limited for atmospheres containing carbon species, such as Mars or Venus, where the non-equilibrium wake largely contributes to afterbody heating. Consequently, the analysis of afterbody heating for vehicles designed for such planets often relies on numerical models whose validity remains unverified [2]. Moreover, with planned missions to ice giants in this decade by space agencies like NASA and ESA [3], the pressing need for an enhanced comprehension of non-equilibrium flow in expanding configurations becomes evident.The objective of this project is to investigate non-equilibrium flows to attain a comprehensive understanding of the microscopic state of the gas and encapsulate this knowledge within commonly used two-temperature equation numerical models in engineering computations. Specifically, the expanding flow, generated around the edge of a spacecraft, can be replicated through unsteady expansions in expansion tubes. During the expansion process, a reduction in density and translational temperature effectively decelerates non-equilibrium thermochemical processes, allowing the observation of these phenomena within the short time frame available in short-duration facilities through the utilization of spectroscopy. The project's primary objective is thus to develop a numerical model for steady expanding flows that is capable of representing the internal degrees of freedom to an arbitrary detail. This model will be instrumental in analysing spectroscopic data gathered in expansion tube test campaigns. The innovative numerical model will be rooted in the Navier-Stokes equations for a non-equilibrium mixture of excited and ionized species, incorporating terms to represent streamline divergence at the centreline of a test setup designed to produce steady expansion waves and will be based on the axisymmetric Navier-Stokes solver known as FRamework for Overset Simulation of Shock Tubes (FROSST) and the LAgrangian Shock Tube Analysis (LASTA) code [4].[1] Johnston, Christopher O., and Aaron M. Brandis. "Features of afterbody radiative heating for earth entry." Journal of Spacecraft and Rockets 52.1 (2015): 105-119.[2] Edquist, Karl, et al. "Aerothermodynamic design of the Mars Science Laboratory hea

这个项目属于EPSRC的福尔斯：流体动力学和空气动力学在高超音速下，气体的行为表现出非平衡现象，代表了理解和预测高超音速流动的最复杂的方面。在模拟这些现象的主要困难在于占整个流动历史中所涉及的自由度，如各种气体种类和它们的激发状态的众多。此外，现有的热力学和化学数据的特点不充分，现有的非平衡模型仍然具有不确定性。然而，非平衡现象对高速工程应用，特别是在大气层进入飞行器的设计和安全方面具有重要意义。事实上，这些现象显著地影响飞行器空气动力学、热负荷和推进系统效率。一个值得注意的例子是航天器进入行星大气层时所经历的加热。这种加热主要是由于飞行器外缘周围的等离子体膨胀产生的辐射，这些辐射来自处于激发态的气体，远离热力学平衡。通常认为，与对流加热相比，进入地球时的后体辐射可以忽略不计，正如阿波罗的后体辐射计的最小读数所示。然而，随后的研究结果显示，辐射计被校准为错误的波长[1]，对现有的双温度模型在进入地球大气层的车辆尾流中的非平衡流的有效性产生了怀疑。对非平衡现象的理解甚至更局限于含有碳物质的大气，如火星或金星，其中非平衡尾流主要有助于后体加热。因此，为这些行星设计的飞行器的后体加热分析通常依赖于数值模型，其有效性尚未得到验证[2]。此外，随着NASA和ESA等太空机构计划在本十年内对冰巨星的任务[3]，这个项目的目标是研究非平衡流，以获得对气体微观状态的全面理解，并将这些知识封装在常用的两个-工程计算中的温度方程数值模型。具体地说，膨胀流，周围产生的边缘的航天器，可以复制通过非定常膨胀在膨胀管。在膨胀过程中，密度和平移温度的降低有效地减缓了非平衡热化学过程，从而可以通过利用光谱学在短期设施中的短时间内观察这些现象。因此，该项目的主要目标是开发一个数值模型，稳定的扩大流动，是能够代表内部自由度的任意细节。该模型将有助于分析膨胀管测试活动中收集的光谱数据。创新的数值模型将植根于Navier-Stokes方程，用于激发和电离物质的非平衡混合物，在设计用于产生定常膨胀波的试验装置的中心线上，加入一些表示流线发散的项，这些项将以轴对称纳维尔-斯托克斯方程解算器（称为激波管重叠模拟的FRamework（FROSST））和拉格朗日激波管分析（LASTA）代码为基础[4]. [1]约翰斯顿，克里斯托弗O.，Aaron M.布兰迪斯“进入地球后体辐射加热的特征。《太空船与火箭杂志》52.1（2015）：105-119。[2]Edquist，Karl等人，“火星科学实验室热空气动力学设计”，