Investigation On Atomization And Fuel-Air Spatial Distribution Characteristics In Large Gradient Shear Mixing Flow With Low Pressure

The embedded rocket ramjet has the characteristics of high specific impulse,high push-weight ratio and wide working range.The high-quality fuel atomization and reasonable spatial distribution of fuel and air are essential to keep the engine operating stably and efficiently in the high-altitude condition and bad environment.To organize low pressure combustion in large gradient sub-super shear mixing layer of an embedded rocket ramjet,the atomization and the spatial distribution of fuel and air in the sub-super large gradient shear mixing layer are studied numerically and experimentally.Different fuel injection schemes were designed and an experimental system was established for the measurement of fuel atomization characteristics.In the meanwhile,a simplified calculation model was built.The effects of injection scheme and shearing layer aerodynamic parameters on fuel atomization characteristics and fuel-air spatial distribution were investigated.Main results are concluded as follows:(1)The atomization characteristics such as atomization particle size,N value(particle size distribution index),volume fraction were studied under different fuel injection schemes and pneumatic parameters.It is found that the fuel injection pressure has little effect on the atomization characteristics of fuel.The atomization characteristics of the reverse injection are better compared with the vertical injection and forward injection.And when the nozzle position is closed to the tail edge of the supporting plate,the performance of atomization is improved.The atomization performance could be promoted by increasing ambient pressure,as well as the Mach number and the temperature of supersonic and subsonic flow.The dimensionless relation of SMD is fitted,and the deviation between the calculated value and the test result is less than 15%.(2)A numerical method based on CLSVOF is used to simulate the breakup process of the jet liquid column in the sub-super shear mixing layer.Results show a large number of surface waves are formed in the breakup process,and the jet always breaks at the trough of the surface wave.Comparing the fitting value of dimensionless empirical relation with the wavelength obtained by simulation,it is proved that the mechanism of surface wave can be explained by K-H instability.Two kinds of secondary breakup processes of droplets were captured and the mechanism of tail-clamping of droplets was preliminarily verified.(3)Through numerical calculation and experimental study,the effects of injection scheme and aerodynamic parameters on the spatial distribution of fuel and gas are investigated.The jet trajectory will deflect to the subsonic flow and the penetration depth will be increased if the nozzle position is away from the trailing edge of the supporting plate.The penetration depth of vertical injection is the largest,and the penetration depth of forward injection increases with the increase of angle from 45°to 60°.The penetration depth of reverse injection is the same as that of forward injection.With the decrease of ambient pressure,the fuel trajectory will deflect to the subsonic flow and the penetration depth will gradually increase,meanwhile the evaporation position will move towards the direction of flow.The increase of Mach number of supersonic flow causes the deflection angle to change to supersonic flow,the penetration depth will decrease,and the position from the beginning of evaporation to the end of the branch plate will first become longer and then shorter.The temperature of supersonic flow has little effect on the fuel trajectory,but the fuel evaporation position will advance gradually,and the dimensionless equation of penetration depth is fitted,and the deviation between the calculated value and the experimental results is less than 15%.