Experimental And Numerical Investigations Of The Flowing In The Combustion-Driven Gas-Dynamic CO₂ Laser

The process of flowing in a combustion-driven gas-dynamic CO2 laser was studied from theory and experiments in this paper. To begin with, a brief introduction of gas-dynamic laser is given, and the formula for calculating the starting pressure ratio is derived.As to the experimental study, the cold flow test about the injection of gas-dynamic CO2 laser is conducted in this paper, the flowrate characteristics and atomization characteristics of this special injection are given. The law how the controlling parameters, such as the pressure before injecting, total pressure of the gas, the survey distance to exit, affect the discharge coefficient and the mean diameter of the spray is analyzed. Some conclusions can be drawn from the experiment. First, the discharge coefficient of liquid is almost constant when the pressure before injecting is high enough, but the discharge coefficient of gas fluctuates because of the influence of liquid flowing. Second, when the total pressure of gas is low, under the same total pressure, increasing the pressure before injecting or under the same the pressure before injecting, lowing the total pressure of gas make the mean diameter smaller.As to the simulation, three-dimensional N-S equations and two-phase flow model, in which the liquid toluene spray as discrete particles was considered, were employed to describe the turbulent combustion processes in the combustion chamber. The mass and energy transfer between the two phases were calculated by the droplet evaporation model, and the Arrehnius model was used to obtain the gas chemical reaction rate. The details of 3D flow field, the distributions of temperature and compounds were obtained by solving the equations. By comparing the results of two different lengths of xiaofang, it is found that the combustion efficiency with a smaller length is higher. Moreover, the effect of various structure, such as the lengths of dafang, the angle between xiaofang and dafang is analyzed with a 2D model. The results show that the combustion chamber with smaller angle and length of dafang is better.Finally, the two dimensional flow in the diffuser is calculated, the results show that the change of Ma makes an effect to the performance of the diffuser. Owing to the accretion of Ma, the action of oblique shock waves and the boundary layer pricks up, the flow separates from the wall where the shock waves impinge on the boundary layer more quickly, the cluster of diamond shock waves becomes larger. Moreover, by comparing the change of flow field under different structure parameter, it is found that the augment of length of constant area section alter the structure of fluid field little, a smaller area ratio and larger angle of compression section make the diffuser working better. These are of use to the optimal structure design to the combustion-driven gas-dynamic CO2 lasers.