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

该项目属于 EPSRC：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。模拟这些现象的主要困难在于考虑整个流动历史中涉及的多个自由度，例如各种气体种类及其激发态。此外，现有的热力学和化学数据没有充分表征，现有的非平衡模型仍然存在不确定性。然而，非平衡现象对高速工程应用具有至关重要的影响，特别是在大气进入飞行器的设计和安全方面。事实上，这些现象显着影响车辆空气动力学、热负荷和推进系统效率。一个著名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，处于激发态的气体产生辐射，远离热力学平衡。通常认为，与对流加热相比，进入地球的尾部辐射可以忽略不计，如最小温度所示阿波罗号尾部辐射计的读数。然而，随后的发现表明，辐射计校准的波长是错误的[1]，这使人们对现有的双温度模型在车辆进入地球大气层后非平衡流的有效性产生了怀疑。对于含有碳物质的大气（例如火星或金星），对非平衡现象的理解更加有限，其中非平衡尾流很大程度上有助于尾部加热。因此，针对此类行星设计的车辆的尾部加热分析通常依赖于其有效性尚未得到验证的数值模型[2]。此外，随着美国国家航空航天局 (NASA) 和欧洲航天局 (ESA) 等航天机构计划在本十年内对冰巨星执行任务 [3]，加强对膨胀结构中非平衡流动的理解的迫切需要变得显而易见。该项目的目标是研究非平衡流动。平衡流以获得对气体微观状态的全面了解，并将这些知识封装在工程计算中常用的二温度方程数值模型中。具体来说，航天器边缘周围产生的膨胀流可以通过膨胀管中的不稳定膨胀来复制。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，从而允许通过利用光谱学在短持续时间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稳定膨胀流动的数值模型，该模型能够表示任意细节的内部自由度。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激发态和电离态非平衡混合物的纳维-斯托克斯方程，纳入了表示测试装置中心线流线发散的术语，该测试装置旨在产生稳定的膨胀波，并将基于轴对称纳维-斯托克斯求解器，称为激波管重叠模拟框架 (FROSST) 和拉格朗日激波管分析 (LASTA) 代码[4].[1]克里斯托弗·O·约翰斯顿和亚伦·M·布兰迪斯。 “进入地球的尾部辐射加热的特征。”航天器与火箭杂志52.1（2015）：105-119.[2]埃德奎斯特，卡尔，等人。 《火星科学实验室热源气动热力学设计》