Numerical Analysis of Performance of DF Chemical Laser With a Radial-Expansion Nozzle Array According to D₂ Injection Angles

It is chemical laser system that can be used for not only new strategic weapon system for the military purpose, but also a manufacturing tool in industrial areas due to the characteristic of high power laser beam in megawatt range. In order to increase laser beam power in the chemical laser system, mixing efficiency of fuel and oxidant should be higher and more excited molecules be produced by mean of chemical reaction. Basically, the production of a lot of excited molecules in the laser cavity results from the high mass flow rates of fuel and oxidant as well as high mixing and reaction efficiencies, however, it is difficult for the planar nozzle array which has been widely used until now to supply high mass flow to the chemical laser cavity. A radial expansion nozzle array as an innovated alternative of the planar nozzle system is designed. The laser beam generation in this system is achieved by mixing F atom from supersonic nozzle and D₂ molecule from the holes of round-bended supply line which are distributed with zigzag configuration, hence the reaction surface will be stretched. Consequently, it is expected that more excited molecules will be produced and population inversion also be higher. Based on that the fuel injection angle with mainstream has a big influence of performance of supersonic combustor, the effects of D₂ injection angles with the main F flow on mixing enhancement and laser beam power are numerically investigated. The results are discussed by comparison with three cases of D₂ injection angles; 10°, 20° and 40° with the main flow direction. Major results reveal that the area where the DF(1) excited molecules as a representative product in the DF chemical laser system are produced becomes larger when the D₂ injection angle increases. The reason is that the surface of chemical reaction is larger and the field temperature is higher with increase of the D₂ injection angle. And in all the vibrational transitions, the distributions of the highest maximum small signal gains are observed near the inlet when the D₂ injection angle is 40°. As the D₂ injection angle increases, the values of the maximum SSG are higher and the area including the high gains is also wider for the most part of domain. Based on these maximum SSG distributions, the highest power of laser beam is expected to be generated when the D₂ injection angle is 40°, namely higher. However, the range of population inversion becomes narrower as the D₂ injection angle increases, because the collision of molecules or atoms happens more often so that the relaxation time will be reduced as the cavity pressure caused by the high D₂ injection angle with the main flow direction increases.