红外与激光工程, 2018, 47 (12): 1218005, 网络出版: 2019-01-10  

大口径主镜热边界层热控对成像质量影响分析

Effect of thermal control of thermal boundary layer on image quality with large-aperture primary mirror
谭玉凤 1,2,3,*王继红 1,2任戈 1,2任晓坜 1,2,3杨欣欣 1,2,3谢宗良 1,2,3贺璧 1,2,3
作者单位
1 中国科学院光电技术研究所, 四川 成都 610209
2 中国科学院光束控制重点实验室, 四川 成都 610209
3 中国科学院大学, 北京 100049
摘要
随着望远镜口径的增大, 主镜热惯性增大, 主镜温度相对于环境温度的滞后性引起反射面热边界层形成热湍流波动, 严重影响望远镜成像质量。介绍了一种基于CFD仿真和光程差累积的计算方法评估主镜反射面热边界层的湍流波动对成像质量的影响。以3.0 m口径的主镜为例, 仿真计算了自然对流下和强迫对流下不同温升的反射面热边界层分布, 将热边界层的流场参数转化成折射率场分布, 采用光程差累积法得到反射面热边界层的成像质量。结果可以定量地描述反射面热边界层对成像质量的影响; 验证了现有天文观测要求主镜反射面与环境温差小于±2 K的合理性; 同时证明了主镜反射面热控措施使得强迫对流下的光程差比自然对流下的下降了一个数量级, 显著提高了主镜视宁度, 进一步表明反射面热控措施对改善成像质量具有重要意义。
Abstract
With the increase of the aperture of the telescope, the inertia of the primary mirror increases sharply. Both of the temperature difference with optical surface and ambient air and turbulence fluctuation at thermal boundary layer result in heavy mirror seeing, directly influence the optical quality. A method based on computational fluid dynamics and optical path difference integrated calculation was proposed to evaluate the optical quality due to turbulence fluctuation at thermal boundary layer. To verify this method, the thermal boundary temperature distribution of a 3.0 m aperture primary mirror was simulated and calculated in different temperature warmer optical surface in natural and forced convection, respectively. Then, the temperature field was transformed to be refractive index field by corresponding equations. The optical performance of thermal boundary layer was calculated by optical path difference integration at the refractive index field. The results can quantitatively describe the effect on optical quality from the thermal boundary layer, which has made up for the deficiency of the existing seeing test. Meanwhile, it is verified that the existing astronomical observation requires the temperature difference between the primary mirror and the ambient air less than 2 K. The primary mirror thermal control system makes the optical path difference in forced convection decrease by an order of magnitude than that in the natural convection, which significantly improves the primary mirror seeing. Furthermore, it is indicated that the thermal control at optical surface is of great significant to improve the image quality.

谭玉凤, 王继红, 任戈, 任晓坜, 杨欣欣, 谢宗良, 贺璧. 大口径主镜热边界层热控对成像质量影响分析[J]. 红外与激光工程, 2018, 47(12): 1218005. Tan Yufeng, Wang Jihong, Ren Ge, Ren Xiaoli, Yang Xinxin, Xie Zongliang, He Bi. Effect of thermal control of thermal boundary layer on image quality with large-aperture primary mirror[J]. Infrared and Laser Engineering, 2018, 47(12): 1218005.

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