激光内通道热效应研究
本文选题:激光传输 + 内通道 ; 参考:《中国科学院大学(中国科学院光电技术研究所)》2017年硕士论文
【摘要】:激光在内通道中传输时,通道内的气体及光学、结构元件会吸收激光能量,使内通道中产生热积累,出口处产生像差,降低激光远场的能量集中度。本文研究激光在内通道中传输的光场、流场及热边界层耦合方法,对激光在不同结构内通道传输时产生的热效应综合分析,能够高效地对内通道光传输质量进行评估。课题基于流体力学方程组和光传输方程,利用现有的计算流体力学软件FLUENT对激光在内通道传输中的流场进行求解,然后自定义程序将光场以热源形式加入流场。建立了通用的激光内通道光场、流场耦合分析模型。首先对普通直管、周期抽气和双层抽气三种内通道结构进行分析比较,仿真结果表明,普通直管中管壁热边界层会扩散至主光路,热积累温度最高,主光路最大温升达到0.7K;周期抽气内通道热积累及出口处像差较小,但工程实现难度较高;采用双层抽气结构热边界层控制最好,主光路温升仅为0.1K,出口处像差也较小,为理想的内通道结构。接着介绍了内通道中反射镜在激光辐照下仿真分析,通过有限元分析热力耦合,比较了硅、蓝宝石、碳化硅和熔石英四种基底材料的反射镜在相同能流密度的阵列激光辐照下的温度分布和面形变化,结果表明,硅和碳化硅反射镜温升及面形像差较小。以硅镜为例,分别对阵列和中空激光光束辐照下的反射镜数值仿真得到,阵列激光辐照下温升及像差较大,这对像差校正提出更高的要求。开展了激光在复杂双层内通道流场传输时产生的气体、管壁和镜面热效应综合仿真分析。首先对流场结构进行高质量的结构化网格划分,在仅考虑气体热效应和气体及管壁镜面两种情况下,对无通风内通道热效应进行仿真,然后对通入气体后的内通道流场及光场计算。结果表明,在通入气体情况下出口处相位PV值要比无通气情况有量级上的下降。通气情况下数值计算结果与实验测量结果相符。根据已验证的仿真模型对不同入口气体流量情况下数值计算,优化出较为合理的气体入口流量,为内通道热管理工程实现提供了理论分析和数据支撑。
[Abstract]:When the laser is transmitted in the inner channel, the gas and optics in the channel and the structural elements will absorb the laser energy, which will lead to heat accumulation in the inner channel and aberration at the exit, thus reducing the energy concentration in the far field of the laser. In this paper, the coupling method of light field, flow field and thermal boundary layer is studied. The thermal effect of laser propagating in different internal channels is analyzed synthetically, and the quality of optical transmission in inner channel can be evaluated efficiently. Based on the fluid dynamics equations and optical transmission equations, the flow field in the laser inner channel is solved by using the existing computational fluid dynamics software fluent, and then the light field is added into the flow field in the form of heat source by custom program. A general coupling analysis model of laser inner channel light field and flow field is established. First of all, the structure of three internal channels, namely, ordinary straight pipe, periodic air extraction and double-layer air extraction, are analyzed and compared. The simulation results show that the thermal boundary layer of the wall of the pipe will diffuse to the main light path, and the heat accumulation temperature is the highest. The maximum temperature rise of the main light path is 0.7K, the thermal accumulation and the aberration at the exit of the periodic pumping channel are small, but the engineering implementation is more difficult, the heat boundary layer of the double-layer exhaust structure is the best, the temperature rise of the main light path is only 0.1K, and the aberration at the exit is smaller. It is an ideal internal channel structure. Then the simulation analysis of the mirror in the inner channel under laser irradiation is introduced, and the comparison of silicon and sapphire by finite element analysis is given. The temperature distribution and surface shape change of the mirrors of silicon carbide and fused quartz under the same energy flow density array laser irradiation show that the temperature rise and surface difference of silicon and silicon carbide mirrors are small. Taking silicon mirror as an example, the numerical simulation of reflector irradiated by array and hollow laser beam shows that the temperature rise and aberration are larger under array laser irradiation, which puts forward higher requirements for aberration correction. The thermal effects of gas, tube wall and mirror surface produced by laser propagation in a complex double-layer inner channel are simulated and analyzed. First of all, the flow field structure is divided into high quality structured meshes. The thermal effects of the inner passage without ventilation are simulated by considering only the thermal effect of gas and the mirror surface of the tube wall. Then the flow field and light field of the inner channel are calculated. The results show that the value of phase PV at the exit is lower than that in the case of no ventilation. The numerical results under ventilation are in agreement with the experimental results. According to the verified simulation model, the reasonable inlet gas flow is optimized, which provides theoretical analysis and data support for the thermal management engineering of the inner channel.
【学位授予单位】:中国科学院大学(中国科学院光电技术研究所)
【学位级别】:硕士
【学位授予年份】:2017
【分类号】:TN24
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