本文選題：激光傳輸 + 內通道��； 參考：《中國科學院大學(中國科學院光電技術研究所)》2017年碩士論文

【摘要】：激光在內通道中傳輸時,通道內的氣體及光學、結構元件會吸收激光能量,使內通道中產生熱積累,出口處產生像差,降低激光遠場的能量集中度。本文研究激光在內通道中傳輸的光場、流場及熱邊界層耦合方法,對激光在不同結構內通道傳輸時產生的熱效應綜合分析,能夠高效地對內通道光傳輸質量進行評估。課題基于流體力學方程組和光傳輸方程,利用現有的計算流體力學軟件FLUENT對激光在內通道傳輸中的流場進行求解,然后自定義程序將光場以熱源形式加入流場。建立了通用的激光內通道光場、流場耦合分析模型。首先對普通直管、周期抽氣和雙層抽氣三種內通道結構進行分析比較,仿真結果表明,普通直管中管壁熱邊界層會擴散至主光路,熱積累溫度最高,主光路最大溫升達到0.7K;周期抽氣內通道熱積累及出口處像差較小,但工程實現難度較高;采用雙層抽氣結構熱邊界層控制最好,主光路溫升僅為0.1K,出口處像差也較小,為理想的內通道結構。接著介紹了內通道中反射鏡在激光輻照下仿真分析,通過有限元分析熱力耦合,比較了硅、藍寶石、碳化硅和熔石英四種基底材料的反射鏡在相同能流密度的陣列激光輻照下的溫度分布和面形變化,結果表明,硅和碳化硅反射鏡溫升及面形像差較小。以硅鏡為例,分別對陣列和中空激光光束輻照下的反射鏡數值仿真得到,陣列激光輻照下溫升及像差較大,這對像差校正提出更高的要求。開展了激光在復雜雙層內通道流場傳輸時產生的氣體、管壁和鏡面熱效應綜合仿真分析。首先對流場結構進行高質量的結構化網格劃分,在僅考慮氣體熱效應和氣體及管壁鏡面兩種情況下,對無通風內通道熱效應進行仿真,然后對通入氣體后的內通道流場及光場計算。結果表明,在通入氣體情況下出口處相位PV值要比無通氣情況有量級上的下降。通氣情況下數值計算結果與實驗測量結果相符。根據已驗證的仿真模型對不同入口氣體流量情況下數值計算,優(yōu)化出較為合理的氣體入口流量,為內通道熱管理工程實現提供了理論分析和數據支撐。
[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.
【學位授予單位】：中國科學院大學(中國科學院光電技術研究所)
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TN24

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