Numerical Analysis and Wind Tunnel Validation of Low-Temperature Ablators undergoing Shape Change
Numerical Analysis and Wind Tunnel Validation of Low-Temperature Ablators undergoing Shape Change
复制标题
低温烧蚀体形状变化的数值分析和风洞验证
DOI：
10.1016/j.ijheatmasstransfer.2021.121430
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发表时间：
2021
影响因子：
5.2
通讯作者：
Alessandro Turchi
中科院分区：
文献类型：
--
作者：
D. Bianchi;M. T. Migliorino;M. Rotondi;Alessandro Turchi
烧蚀材料地面试验的目的是提供高超声速再入条件下材料性能的关键数据。这通常在等离子风洞设施中进行。然而，为了复制真实的飞行条件，面临着不可忽视的技术挑战，例如诱导与空间相关的烧蚀材料的后退，这需要足够高的入流总马赫数，和/或再现实际的高超音速流速度，这需要足够高的入流马赫数。通常，提供一种需求的地面设施缺乏另一种需求，反之亦然。一种可能的解决办法是在连续高超音速吹扫风洞中使用低温烧蚀材料，在这种风洞中，可以在合理的低总温条件下进行具有相当大的形状变化效应的空气动力学和烧蚀试验，而且试验持续时间可以承受。这些物质很容易获得，它们的升华或烧蚀方式可以用理论相当准确地描述。这项工作的目标是数值表征此类材料在高超音速条件下的形状变化，同时根据文献数据和专门的实验地面测试活动进行验证。数值计算过程依赖于考虑材料形状变化的自组织网格生成/演化策略，并基于随后的稳态计算流体动力学（CFD）计算以及可定制的气体-表面相互作用壁边界条件。初步的数值模拟有助于设计拟在冯·卡门研究所H-3高超音速风洞中进行的实验，特别是确定密封舱的几何形状和尺寸，以便最大限度地减少烧蚀造成的形状变化。通过对樟脑表面反应热力学和动力学的分析，确定樟脑为最适合用于实验的低温烧蚀剂。从计算流体动力学方法的结果进行了比较，首先与文献实验测试的情况下，然后与先前设计的实验，具有樟脑子规模胶囊，基本的优点和限制所采用的数值方法。所获得的数值和实验结果强调，它是如何可能获得一个相对较小的曝光时间的相关形状变化，通过使用低温烧蚀在连续高超音速吹落式风洞。因此，从这项工作的结果可以用来支持实际的隔热罩的设计和尺寸和胶囊的空气动力学和稳定性的分析，占形状变化的影响，通过建立一个适当的飞行和地面条件之间的相似性。
Ground testing of ablative materials aims at providing critical data on the material behavior under hypersonic reentry conditions. This is normally done in plasma wind tunnel facilities. However, non-negligible technical challenges are faced in order to duplicate the real flight conditions, such as inducing the recession of space-relevant ablative materials, which requires sufficiently high inflow total enthalpies, and/or reproducing the actual hypersonic flow velocity, which requires sufficiently high inflow Mach numbers. Often, ground facilities which are providing one requirement are lacking the other one and vice-versa. A possible solution is to use low-temperature ablators in continuous hypersonic blow-down tunnels, where aerodynamic and ablative tests with considerable shape change effects may be performed under reasonably low total temperature conditions and with affordable test durations. These substances are readily available, and they sublimate or ablate in a fashion that can be described fairly accurately by theory. This work has the objective to numerically characterize the shape change of such materials in hypersonic conditions, concurrently providing a validation against literature data and from a dedicated experimental ground test campaign. The numerical procedure relies on ad-hoc mesh generation/evolution strategies taking into account the material shape change, and is based on subsequent steady-state Computational Fluid Dynamics (CFD) computations coupled with a customizable gas-surface interaction wall boundary condition. Preliminary numerical simulations helped the design of the experiments to be carried out in the von Karman Institute (VKI) H-3 hypersonic wind tunnel, in particular for the identification of capsule geometry and size in order to maximize the shape change caused by ablation. Subsequently, camphor is identified as the most suitable low-temperature ablator to be used in the experimental campaign after a thorough analysis of its surface reaction thermodynamics and kinetics. Results from the CFD approach are first compared with a literature experimental test case and then with those of the previously designed experiments, featuring a camphor sub-scale capsule, underlying advantages and limits of the numerical procedure adopted. The obtained numerical and experimental results underline how it is possible to obtain a relevant shape change for relatively small exposure times by using low-temperature ablators in continuous hypersonic blow-down wind tunnels. Hence, results from this work can be used to support the design and sizing of the actual heat shield and the analysis of the capsule’s aerodynamics and stability, accounting for shape change effects, by establishing an appropriate similitude between in-flight and on-ground conditions.