| Bipropellant liquid rocket engine is the main power in the space propulsion system,forming the foundation of the space industry.In bipropellant liquid rocket engine,atomization,evaporation and mixing process of liquid fuel and oxidant is the key factor that affects the efficiency and stability of the engine,for its uniformity and efficiency directly affect the stability of combustion and combustion efficiency.So the atomization characteristics and atomization mechanism of the injection unit is of great significance to the design of engine.Liquid/liquid coaxial swirl injector is widely used for its high efficiency and good effect of atomization.In this text,taking liquid/liquid swirling jets as the research object,the spray structure,liquid sheet breakup characteristics,liquid jet instability and flow field characteristics were studied.Through this study,the understanding on the breakup mechanism of liquid/liquid swirling jets could be deepen,and theoretical basis on the design of injector and combustion chamber for bipropellant liquid rocket engine could be provided.The spray structure and breakup characteristics of liquid/liquid swirling jets were studied experimentally.The experiment system employed for the present study is mainly composed of workbench,liquid supply system,liquid/liquid swirl injector,Optical camera system and particle size measurement system.Through the analysis of the spray image,breakup process and spray structure under different conditions were investigated.The influence of the injection condition on the breakup characteristics of liquid/liquid swirling jets was obtained,thus the influence mechanism of injection We number was clarified.The spray area was divided into four regions:primary breakup zone,secondary breakup zone,collision and coalescence zone,and the distribution characteristics of droplets at different zones were obtained.Based on the linear instability theoty,the dispersion equation of liquid/liquid coaxial annular swirl liquid sheet was established.The dispersion equation was solved numerically by Muller method in temporal mode,and its accuracy was validated.The instabilty of para-sinuous and para-varicose mode disturbance were analysis,clarified that the para-sinuous mode disturbance was the dominant mode.Through the analysis of the disturbance growth rates at different m order,the dominant m order was clarified.The influence of dimensionless parameters on dominant disturbance growth rates and dominant disturbance wave number were discussed,thus the influence mechanism of the swirl strength,liquid velocity ratio,liquid gas density ratio,surface tension and liquid curvature on liquid/liquid coaxial annular swirl liquid sheet was clarified.Based on large eddy simulation and the VOF method,the liquid gas multiphase flow large eddy simulation solver for liquid/liquid coaxial swirling jets was implemented in OpenFOAM.In the LES solver,adaptive refinement grid method was coupled.Besides,the LES solver was compiled on computer cluster,and parallel computing between nodes was implemented,thus provided a powerful tool for the numerical investigation of breakup mechanism of liquid/liquid coaxial swirling jets.The liquid filling process inside injector was simulated using the solver.Through the analysis of the flow field inside the injector based on the simulation results,the velocity change rules in each part of the injector were revealed.The influence of injection pressure on liquid distribution inside the injector,liquid film thickness and velocity distribution at the nozzle exit were obtained.And the influence of nozzle exit velocity on the liquid sheet cone angle was clarified.The liquid sheet breakup process of the liquid/liquid coaxial swirling jets was simulated by using the larger eddy simulation solver.The spray structure and flow filed of the liquid/liquid coaxial swirling jets were obtained.Based on the simulation results,breakup morphology of the liquid/liquid coaxial swirling jets was analyzed,including the spray structure and the liquid sheet form in the near region of the nozzle.Through the analysis of the liquid sheet velocity and velocity field distribution,the formation mechanism of recirculation region was revealed.Besides,the influence mechanism of liquid gas interaction on the breakup characteristics was revealed.The characteristics of surface wave and its generation mechanism were clarified by analyzing the surface wave structure at the near region of the nozzle.The ligament breakup mechanism was investigated.It revealed that the breakup of ligaments was Rayleigh type which is driven by surface tension.Besides,the breakup length scale of ligaments was identified. |
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