| Small thrust liquid rocket engines are widely used in space shuttles, spacecrafts, kinetic interceptors, satellites and multi-stage vehicles. They play a very important role in orbit trimming, attitude control, the docking, rendezvous and landing of the space flight vehicle, etc., and become one of the most important parts of modern aerospace vehicles. Meanwhile, proper organization of the spray combustion processes of the propellant in the liquid rocket engine is of great significance in its working realiablity, working life, economical efficiency and stability. On the background of the small scale liquid rocket engines, by using of HAN-Based liquid propellant simulated medium, three kinds of nozzles are designed:the pressure-swirl nozzle, the impinging nozzle and the air-blast nozzle. The experiment and numerical simulation of the spray characteristics of the three nozzles are conducted both in the atomosphere and in the small scale simulated combustion chamber. The main research contents and results are as follows:(1) The spray angle of the pressure-swirl nozzle is quantitively tested by using of high speed camera system. The results show that the spray angle increases with the injection pressure for the pressure-swirl nozzles with different structure. For the two swirl slots pressure-swirl nozzle, the spray angle grows at first and then decrease with increasing of the HAN-Based liquid propellant simulated medium’s viscosity; while for the four swirl slots pressure-swirl nozzle, the spray angle decreases linearly with increasing of the liquid viscosity. As the injection pressure and the liquid viscosity are fixed, the larger the nozzle outlet diameter is, the greater the spray angle will be.(2) The distribution characteristics of the spray parameters in the spray field of the pressure-swirl nozzle are tested by using of Particle Dynamic Analyzer (PDA) system both in the atomosphere and in the small scale simulated combustion chamber. The results show that, for the pressure-swirl nozzles with different outlet diameters, the liquid droplets’Sauter mean diameter (.D32) decreases with increasing of the injection pressure. Under the same injection pressure, the smaller the nozzle outlet diameter is, the smaller the liquid droplets’ D32will be. For the pressure-swirl nozzle with the outlet diameter Du=1mm, the axial velocity v:of the liquid droplets decreases first and then changes small along the axial direction; while the liquid droplets’ v: increases first and then decreases along the axial direction for the pressure-swirl nozzle with the outlet diameter Du=2mm.(3) The distribution characteristics of the spray parameters in the spray field of the impinging nozzle are tested by using of PDA system both in the atomosphere and in the small scale simulated combustion chamber. The results show that along the axial direction, the liquid droplets’ arithmetic mean diameter D10and Sauter mean diameter D32increase while v: gradually decreases in the spray field of the HAN-Based liquid propellant simulated medium. The higher the injection pressure is, the smaller the liquid droplets’D10and D32will be. Under the pressure in the range of0.8～1.8MPa, the liquid droplets’v:increases with the injection pressure; however, the liquid droplets’v: has a small change under the pressure in the range of1.8～2.6MPa. Under the same injection presure, with the liquid viscosity increasing, the liquid droplets’D10and D32increases but the liquid droplets’ v: decreases. Moreover, under the same injection pressure and liquid viscosity condition, both the liquid droplets’ mean diameter and the axial velocity are larger than that in the atomosphere.(4) The distribution characteristics of the spray parameters in the spray field of the air-blast nozzle are tested by using of PDA system both in the atomosphere and in the small scale simulated combustion chamber. The results show that the liquid droplets’mean diameter D10and D32increase along the axial direction with fluctuation while the liquid droplets’axial velocity v: decreses in the spray field of the HAN-Based liquid propellant simulated medium. As the liquid injection pressure is fixed, the higher the gas injection pressure, the smaller the liquid droplets’D10and D32and the larger the liquid droplets’v:. As the gas injection pressure is fixed, the higher the liquid injection pressure, the larger the liquid droplets’D10and D32, but the effect of the liquid injection pressure on the liquid droplets’ v: is small.(5) The coefficient of variation (Cv) is introduced to quantify the distribution uniformity of the spray parameters in the spray field for all the three kinds of nozzles, i.e., the pressure-swirl nozzle, the impinging nozzle and the air-blast nozzle both in the atomosphere and in the small scale simulated combustion chamber. The results indicate that both the injection pressure and the restriction of the wall affect the distribution uniformity of spray parameters. The distribution uniformities of the pressure-swirl nozzle and the airblast nozzle in the atomosphere are better than those in the simulated chamber. While for the impinging jet nozzle, the droplets’mean diameter in the simulated chamber has a better uniform distribution than that in the atomosphere. At the radial position r<12mm, the droplets’ axial velocity v2has a better distribution uniformity in the simulated chamber; however, at the further radial position r>15mm, the distribution uniformity of v: in the atomosphere is better than that in the simulated chamber.(6) Based on the VOF model, a three-dimensional unsteady gas/liquid two-phase flow modle of the pressure-swirl nozzle is established and the flow properties of the HAN-Based liquid propellant simulated medium in the nozzle are investigated numerically. The simulated results indicate that the changing of the gas/liquid interface in the pressure-swirl nozzle can be catched by the model. The air core in the nozzle swirls with the ambient liquid, and a gas-liquid mixture region is formed close to the gas/liquid interface. The spray angle decreas with time going on and tends towards to a constant value. The longer the swirl chamber, the smaller the spray angle; the samller the nozzle convergence angle, the smaller the spray angle; and the greater the liquid viscosity, the smaller the spray angle. The calculated spray angle agrees well with the experimental value.(7) Based on the experiment results of the pressure-swirl nozzle, a three-dimensional unsteady model including the discrete phase model (DPM) is established to simulate the spray characterisctics of the HAN-Based liquid propellant simulated medium both in the atomosphere and in the small scale simulated chamber. The simulated results indicate that increasing the injection pressure contributes to refine the liquid droplets’ diameter and improve the liquid velocity. However, it will go against the atomization effect to increase the liquid viscosity. Under the same injection condition, the liquid droplets’diameter in the simulated chamber is smaller than that in the atomosphere, while the difference of the liquid droplets’velocities in the two environments is small. The simulated results agree well with the expreriment ones, indicating that the proposed model can be used to simulate the spray characterisctics of the pressure-swirl nozzle.(8) Based on the experiment results of the impinging nozzle, a two-dimensional unsteady model including the DPM model is established. And the spray characterisctics of the HAN-Based liquid propellant simulated medium both in the atomosphere and in the small scale simulated chamber are simulated. The results show that in the atomosphere, after the impinging of the two jets, a symmetrical cone-shaped spray field is formed toped with the impinging point, and the liquid mass fraction presents a shuttle distribution. The larger the impinging angle is, the further the liquid droplets spread, and the more the small diameter liquid droplets appear in the center of the spray field. The larger the liquid viscosity is, the bigger the liquid droplets’diameter D32and the smaller the liquid droplets’v: will be. In the simulated chamber, with the restriction of the chamber wall, the liquid mass fraction distribution shows fan shaped rather than shuttle shaped in the atomospher. The larger the impinging angle is, the smaller both the liquid droplets’diameter D32and the liquid droplets’ v:will be. Under the same injection pressure, both.D32and v:in the atomosphere are smaller than those in the simulated chamber. The simulated results agree well with the expetimetal ones, indicating that the proposed model can be used to simulate the spray characterisctics of the impinging nozzle. |
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