Numerical Study Of Gain Generator's Structure And Operation Mode Of Continuous Wave DF/HF Chemical Lasers

The continuous wave (CW) deuterium fluoride/hydrogen fluoride chemical laser's most urgent demands for development are compactification and mobility after obtaining the highest output power among lasers. As one of the key components in chemical laser, gain generator has great influences on gas transporting, mixing and reacting, which is the most important investigation object for lasers'miniaturization and practicability.In this paper, 3-D simulation method and 1-D simulation method was used to investigate the influences of gain generator's structure and operation mode on mixing enhancement, fuel's saving, etc. Wall recombination model of the fluorine atoms was coupled into the three dimensional program by integrating the surface reaction theory and overall reaction model for bettering the simulation program. And the simulation for the flowfield would be more compatible with reality then.The flowfield of TRIP gain generator was numerically simulated for its excellent mixing effect. The results show that mixing enhancement mostly depends on stretching and wraping the interface between fuel streams, while the helium trip jets'momentum flux are so small that the vortex structure will dissipate quickly which cannot enhance the gas mixing effectively. This technique has a latest use by changing helium jets to the mixture of helium and deuterium. The numerical simulation results show that advantage of mixing ehancement still remains and the deuterium gas in trip jets makes the peak value of the spectrums'small signal gain move upstream a little. The gas pipeline of laser can be simplified when trip jets and secondary stream coming from the same source.Along with the mixing enhancement, trip jets also introduce unfavourable perturbation into the gain medium and shorten the gain region. Thus ramp stuctrue was applied into the gain generator. The simulation results of nitrogen flowfield show that the vortices are generated to enhance the mixing obviously. A HF laser model was established on the basis of ramp nozzle structure. The one dimensional simulation results about the flowfield prove up the important influences of excessive coefficient of primary oxidizer and secondary diluent ratio on laser's operation.According to laser's experiments without diluent, the flowfield was numerically simulated using the 1-D program and the results have a similar distribution with the experimental data. The simulation results also reveal that streams in cavity tend to separate, so the secondary diluent's usage should be treated carefully. As for the primary diluent, considering the method of producing the oxidising gas based on two-region mixing, a gas film nozzle model was established with the helium film injecting at the converging section of the nozzle. The simulation results show that the helium film provides well protection for both the fluorine atoms in primary stream and nozzle wall, and single row film holes with proper interval are more practical to use.The two-region mixing method was applied to the gas film nozzle, and the flowfields with different helium film sources were numerically simulated. The results show that the reaction between streams is delayed a little bit by the helium film. When reducing the primary diluent, the medium can be in a better condition by adjusting mass flux ratio of the other gas fuel. According to restrictions of fluorine atoms'recombination and dissociation critical temperatures, the helium film's permissive flow rate was calculated.In this paper, gain generators with new structure and operation mode were investigated to enhance gas flow mixing, reduce gas fuel usage, etc. These works have great meanings for the compactification and operation stability of the laser. And the relevant results will be helpful for further experimental research.