大型低温风洞内绝热结构的传热特性及试验评价体系研究

In order to solve the heat insulation problem for the large cryogenic wind tunnel some key techniques of internal insulation structure at liquid nitrogen temperature range are studied. Considering the heat insulation performance and strength characteristic of the multi-layer composite insulation structure the structural parameters are optimized and the matching relationship between material characteristic and feature sizes are analyzed. By combining the variable Mach number factor the coupling model between the polygonal aerodynamic profile structure and the cryogenic high-speed airflow load is established, which is used to thoroughly analyze the deformation of the polygonal aerodynamic profile in the specific space and also to explore the profile regulation and control methods. Furthermore, taking the alteration of temperature and pressure into account the cryogenic fluid-solid thermal coupling model of the classic internal insulation structure is created to discover the influence rule of variant factors on the heat transfer characteristic. And on this basis the internal insulation structural sample for cryogenic insulation test is designed and manufactured. According to the test results the theoretical analysis method is validated, and also the test database and the design code are set up.This project is carried out by employing the theoretical analysis and the test research comprehensively, whose purpose is to determinate the design code of the internal insulation structure serving in the cryogenic and variable Mach number environment, to reveal the heat transfer characteristic of the internal insulation structure under the cryogenic fluid-solid thermal coupling conditions， and to set up the test evaluation system of the internal insulation structure adopted in the cryogenic wind tunnel. The research achievements will be directly applied in the large cryogenic wind tunnel construction in our country, which have significant theoretical meaning and engineering value.

为解决大型低温风洞的高效可靠绝热难题，开展液氮温区内绝热结构关键技术研究。考虑多层复合绝热结构的绝热性能与强度特性，优化结构参数，分析材料特性与特征尺寸之间的匹配关系。结合变马赫数因素，建立多边形气动型面结构与低温高速气流载荷耦合模型，深入分析特定空间内多边形气动型面形变规律，探索型面调节和控制的方法。继而综合考虑温度、压力交变的特点，建立典型内绝热结构的低温流-固-热耦合传热模型，揭示不同因素对热传导特性的影响规律。在此基础上，设计加工内绝热结构样件并开展试验，结合试验结果，验证理论分析的有效性，建立试验数据库和设计标准。本项目旨在通过理论分析与试验研究，确定低温变马赫数环境下内绝热结构的设计准则，揭示低温流-固-热多场耦合作用条件下内绝热结构的传热特性，建立低温风洞典型工况下内绝热结构的试验评价体系，研究成果将直接应用于我国大型低温风洞的设计建设，具有重要的理论意义和工程价值。

为解决常规风洞模拟雷诺数偏低的问题，最实用的方法是利用低温风洞降低气流温度达到提高风洞雷诺数模拟的目的。而良好、高效保冷性能的绝热结构已成为低温风洞成功研制的关键技术之一。因此，为解决大型低温风洞的高效可靠绝热难题，项目重点开展了液氮温区内绝热结构关键技术研究。首先，研究了绝热结构传热特性和多边形气动型面防护板强度特性。建立了绝热单元一维导热理论模型，对低温氮气两种极限工况流速下的绝热结构热通量和洞体外表面温度进行了理论计算。基于快速升/降压工况推导了多边形气动型面防护板两侧压差表达式，分析了风洞各部段的防护板两侧压力分布规律。利用激光跟踪仪研究了多边形气动型面防护板的进行调节和控制方法；然后，开展了绝热结构和多边形气动型面防护板优化设计与数值计算。基于数值计算方法对绝热单元进行了优化设计，确定绝热单元的总厚度为150mm，底层、中间层和表层的厚度分别为70mm、10mm、70mm。在此基础上，建立了绝热结构有限元模型，研究了不同工况下绝热结构的强度和传热特性，结果表明绝热结构的热通量低于50W/m2，强度安全系数满足2倍的设计要求。开展了基于大型低温风洞运行工况开展了多边形气动型面防护板结构设计和强度校核，结果表明防护结构强度安全系数满足4倍的设计要求；最后，进行了基于大型低温风洞运行工况的内绝热结构试验研究。搭建了内绝热结构试验平台，加工制造了内绝热结构和防护板试验样件，根据风洞运行工况环境，建立了内绝热结构试验评价体系，开展了内绝热结构验证性试验，试验结构表明内绝热结构设计合理，材料选型恰当，在不同工况下均能满足保冷和强度要求。项目研究成果已经应用于某大型低温风洞绝热结构设计建设。此外，建立的内绝热低温平台弥补了国内可模拟低温风洞环境的试验系统的空缺，同时也为空天、深海等深冷环境下的结构/材料环境适应性试验提供了一个可靠的试验平台。