大型地基太阳望远镜温控技术研究

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	大型地基太阳望远镜温控技术研究
其他题名	Research on Temperature Control Technology for Large Ground-Based Solar Telescope
	张雨辰
学位类型	博士
导师	刘忠 ; 许方宇
	2022-07-01
学位授予单位	中国科学院大学
学位授予地点	北京
培养单位	中国科学院云南天文台
学位专业	天文技术与方法
关键词	大型地基太阳望远镜 2m RST 温控技术视宁度效应热光阑
摘要	随着太阳物理学研究的发展，对下一代大型地基太阳望远镜提出了高时空分辨率、高磁场测量精度的要求。中国科学院云南天文台正筹划建造8米级CGST望远镜。2m RST作为CGST关键技术的试验平台，现已进入工程实施阶段。大型太阳望远镜需要突破的三项关键技术：1、大型主镜拼接。2、望远镜热控。3、低噪声红外探测器。本文聚焦于望远镜热控，研究由此带来的热致视宁度问题。首先，提出一种基于有限元数值仿真手段的热致视宁度评估方法，研究对象包括：热光阑、主镜、副镜。仿真结果表明：三者在同等温升情况下，主镜热致视宁度占主导，不过主镜温控相对容易；在实际工况下，热控压力最大的是热光阑，通过仿真给出了热光阑温控技术指标。接下来，设计了一种高效冷却结构的热光阑，该结构具有温升小、表面温度场分布均匀的优点；同时，对热光阑进行光学优化设计，抑制了杂散光的产生。最后，攻克了光阑测温技术难点，实现了光阑测温系统闭环控制，保证了控温精度。本文对大型地基太阳望远镜温控技术进行了全面而又深入的研究，把热致视宁度效应抑制在合理范围，保证望远镜观测成像质量。视宁度评估方法基于有限元数值模拟。由于热湍流对初值依赖敏感，需借助实验方法评估环境扰动强弱，为仿真边界条件提供参考。仿真基于CFD理论，选用大涡模型（LES）进行高时空分辨率的三维瞬态仿真，获得研究对象周围温度场的时空分布状况。之后，将温度场转化为折射率场，进行渐变折射率介质中的光线追迹仿真研究。由于热致视宁度效应，导致成像面上点列图分布变得弥散，统计一段积分时间内点列图的展宽程度，进而衡量视宁度劣化情况。最终，关于主镜的热致视宁度评估结果得到了经验公式验证；也为热控系统设计提出了技术指标：1、热光阑温升应控制在10℃以内。2、主镜需借助背部吹风方式进行温控，温控目标是镜面温度接近或略低于环境温度。3、副镜热致视宁度效应可忽略，不必进行主动温控。调研分析了现有热光阑存在的技术缺陷。设计了一种具备倒圆锥通光孔外形，并且采用导流翅片式高效冷却结构的热光阑；在冷却液压降损耗较低的情况下，获得了低温升，温度场分布均匀的温控效果。同时，对光阑进行了光学设计，反光面通光孔附近区域优化了倒圆锥夹角，倒圆锥以外区域采用对称式平面反射镜结构。仿真表明，光阑的热控设计与光学设计均符合指标要求。进一步设计了一种背部为扇形镂空结构的主镜，在扇形网格腔体中吹入制冷空气对主镜表面进行温控，优化主镜热致视宁度。光阑温度场测量具有重要意义，是实现温控系统闭环控制的关键。本文提出了两种测温方法，一种是调制法，对加热光源进行调制遮挡后用热像仪获得光阑表面降温曲线，再通过理论分析获得降温曲线的数学模型，拟合得到初始温度场，该方法得到了实验与仿真的验证；还可通过该方法测定时间常数以评估光阑冷却效率。另一种是温差法，通过测量流经光阑的冷却液温升，依据冷却液温升与光阑温度场之间的映射关系，实时获得光阑温度场。光阑温控系统采用温差法实现了闭环控制，保证了控温精度。关于下一代大型地基太阳望远镜的热控问题，本文进行了相关理论与工程技术方面的研究，在2m RST上实现了可靠有效的温控效果，保证了望远镜观测质量；同时为8m CGST望远镜热控系统设计奠定了基础。
其他摘要	With the development of solar physics research, high spatial and temporal resolution, and high magnetic field measurement accuracy are required for the next generation of large ground-based solar telescopes. Yunnan Observatory, Chinese Academy of Sciences is planning to build an 8-meter CGST telescope. 2m RST, as an experimental item for CGST technologies, is now in the engineering implementation stage. Three key technologies need to be broken through for large ground-based solar telescopes: 1. large primary mirror splicing. 2. telescope thermal control. 3. Low-noise infrared detector. This paper focuses on the thermal control of telescopes and investigates the problem of seeing by them. Firstly, a method of thermogenic seeing evaluation based on finite element numerical simulation is proposed, and the research objects include: heat-stop, primary mirror, and secondary mirror. The simulation results show that: under the same temperature rise, the seeing of mirror is dominated, but the temperature control of mirror is relatively easy. Under the actual working conditions, the most difficult thermal control is the heat-stop, and the heat-stop temperature control technology index is given by simulation. Next, an efficient cooling structure of the heat-stop was designed, which has the advantages of small temperature rise and uniform surface temperature field distribution. At the same time, the optical optimization design of the heat-stop suppresses the generation of stray light. Finally, the technical difficulties of heat-stop temperature measurement have been overcome, and the closed-loop control of diaphragm temperature measurement system has been realized to ensure the accuracy of temperature control. The seeing assessment method is based on finite element numerical simulations. Since thermal turbulence is sensitive to the initial value dependence, experimental methods are needed to evaluate the strength of environmental disturbances and to provide a reference for the simulation boundary conditions. Simulation based on CFD theory, and the large eddy model (LES) is selected for the 3D transient simulation with high spatial and temporal resolution to obtain the spatial and temporal distribution of the temperature field around the study object. After that, the temperature field is transformed into the refractive index field and the simulation study of ray tracing in a gradient refractive index medium is performed. Due to the effect of seeing, the distribution of the dot map on the imaging surface becomes diffuse, and the width expansion of the dot map over a period of integration time is counted to measure the seeing. Eventually, the seeing of the primary mirror were verified by empirical equations; technical specifications were proposed for the design of the thermal control system: 1. the temperature rise of the heat-stop should be controlled within 10℃. 2. The primary mirror needs to be temperature controlled with the help of back blowing, and the temperature control goal is to have the mirror surface temperature close to or slightly below the ambient temperature. 3. The secondary mirror thermogenic seeing effect can be ignored, there is no need for active temperature control. The technical defects of the heat-stop were investigated and analyzed. We designed a heat-stop with an inverted cone through-hole profile and a high efficiency cooling structure with inflow fins. The temperature control effect of low temperature rise and uniform temperature field distribution is obtained with low cooling hydraulic drop loss in the heat-stop. At the same time, the optical design of the heat-stop is optimized with an inverted cone angle in the area near the reflective surface through-hole and a symmetrical plane reflector structure in the area outside the inverted cone.The simulation results show that the thermal control design and optical design of the heat-stop meet the requirements. Further designed a main mirror with a fan-shaped hollow structure on the back, blowing cooling air into the fan-shaped grid cavity to temperature control the surface of the main mirror, optimizing the main mirror thermogenic seeing. The heat-stop temperature field measurement is of great significance and is the key to achieving closed-loop control of the temperature control system. In this paper, two temperature measurement methods are proposed, one is the modulation method, in which the heating light source is shaded, and the thermal imaging camera is used to obtain the cooling curve of the heat-stop surface, and then the mathematical model of the cooling curve is obtained by theoretical analysis and then the initial temperature field is fitted, and the method is verified by experiments and simulations. In applications, in addition to heat-stop temperature measurement, heat-stop cooling efficiency can also be evaluated by measuring time-constant. Another method is the temperature difference method, by measuring the temperature rise of the coolant flowing through the heat-stop, based on the relationship between the coolant temperature rise and the diaphragm temperature field, the diaphragm temperature field is obtained in real time. The heat-stop temperature control system uses the temperature difference method to achieve closed-loop control and improve the temperature control accuracy. This paper presents the theoretical and engineering studies on the thermal control of the next generation of large ground-based solar telescope, and achieves reliable and effective temperature control on the 2m RST to ensure the quality of observations of the telescope. The paper also lays the foundation for the design of the thermal control system of the 8m CGST telescope.
学科领域	天文学 ; 天文学其他学科 ; 机械工程 ; 电子、通信与自动控制技术
学科门类	理学 ; 理学::天文学 ; 工学 ; 工学::控制科学与工程
页数	0
语种	中文
文献类型	学位论文
条目标识符	http://ir.ynao.ac.cn/handle/114a53/25783
专题	天文技术实验室
推荐引用方式 GB/T 7714	张雨辰. 大型地基太阳望远镜温控技术研究[D]. 北京. 中国科学院大学,2022.

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