Study On Flow Field Characteristic Of Nozzle And Laser Cavity And Small Signal Gain Characteristic Of Mixing Gasdynamic CO₂ Laser

Mixing gasdynamic CO₂ laser will play an important role in single-soldier tactical laser weapon and laser propulsion. Flow field characteristic in nozzle and laser cavity and small signal gain characteristic of several kinds of mixing gasdynamic CO₂ laser are investigated.Using high speed schlieren experiment and numerical simulation, the basic flow field characteristic of mixing gasdynamic CO₂ laser based on screen nozzle in laser cavity is studied.Distribution of freezing efficiency of nitrogen vibrational energy in donor nozzle of mixing gasdynamic CO₂ laser when the donor gas is pure nitrogen and influence of inlet total temperature and total pressure of the donor nozzle on freezing efficiency of nitrogen vibrational energy are studied. Furthermore, distribution of freezing efficiency of nitrogen vibrational energy in donor nozzle of combustion-driven mixing gasdynamic CO₂ laser, influence of CO₂ and H2 O mole fraction and profile of donor nozzle on freezing efficiency of nitrogen vibrational energy are researched.For the nozzle with certain structure parameters and work parameters, distribution of small signal gain in laser cavity of mixing gasdynamic CO₂ laser based on screen nozzle is studied. Besides, influence laws and influence mechanism of inlet total temperature of donor nozzle, area ratio of donor nozzle, inlet total temperature of assistant nozzle, CO₂ and H2 O mole fraction, half conical angle of expansion section of donor and assistant nozzle, catalyzer species（H2O or He） on small signal gain coefficient in laser cavity are investigated.Flow field characteristic of donor nozzle and assistant nozzle of mixing gasdynamic CO₂ laser based on nozzle type in which laser gas is injected at the throat of donor nozzle is studied. Also, distributions of small signal gain in expansion section and on the outlet plane of donor nozzle are researched. Besides, influence laws and influence mechanism of area ratio of donor nozzle, inlet total pressure of assistant nozzle, injection place of laser gas, inlet total temperature of donor nozzle and assistant nozzle on small signal gain coefficient of mixing gasdynamic CO₂ laser based on nozzle type in which laser gas is injected at the throat of donor nozzle are studied. Finally, mixing gasdynamic CO₂ laser based on screen nozzle and mixing gasdynamic CO₂ laser based on nozzle type in which laser gas is injected at the throat of donor nozzle are compared. The results indicate that the peak value of small signal gain coefficient is higher when nozzle type in which laser gas is injected at the throat of donor nozzle is used, but flow field uniformity is better when screen nozzle is used.Initiative control technology based on periodic temperature excitation is used for mixing gasdynamic CO₂ laser for the first time. Mixing characteristic, flow field characteristic and small signal gain distribution of mixing gasdynamic CO₂ laser using periodic temperature excitation are investigated. Furthermore, influences of excitation amplitude, excitation frequency and excitation place on mixing characteristic of donor/assistant flow and small signal gain coefficient are studied. The results indicate that mixing efficiency of donor/assistant flow can be enhanced and small signal gain coefficient can be improved when periodic temperature excitation with certain excitation amplitude and excitation frequency is imposed on the outlet of assistant nozzle. In order to obtain the maximal small signal gain coefficient, there is an optimal excitation amplitude and an optimal excitation frequency. Compared with the case in which periodic temperature excitation is imposed on the outlet of assistant nozzle, when periodic temperature excitation is imposed on the outlet of donor nozzle, mixing efficiency of donor/assistant flow and small signal gain coefficient both decrease.The scheme of high temperature nitrogen generator of combustion-driven mixing gasdynamic CO₂ laser is designed. Firstly, fuel and oxidant species are chosen. Secondly, a liquid N₂ O supply system is designed. Thirdly, a mono-injector high temperature nitrogen generator using N₂ O and C₇H₈ is designed.Supply characteristic of the liquid N₂ O supply system is studied through experiments. Experimental results indicate that N₂ O can be supplied in liquid state by the designed liquid N₂ O supply system and the mass flow rate of N₂ O is steady. Besides, ignition and combustion performace of N₂ O and C₇H₈ under several rich fuel conditions through igniton experiment of mono-injector nitrogen generator are investigated. Experimental results indicate that successful ignition of N₂ O and C₇H₈ can be realized under all designed rich fuel conditions when choosing proper time sequence and combustions are stable.