Study On The Distributions Of The Concentration,particle Size,velocity And The Detonation Processes Of High Speed Clouds

The dispersion and detonation process of high speed cloud is of great significance in the research of the weapon system safety of the Fuel-Air Explosive(FAE),which is the major research focus at present.However,experimental researches in this area are very difficult to implement,so the exploration and developmet of reliable numerical methods for the study of the high speed cloud gradually become a top priority.Based on computational fluid dynamics(CFD)theory,the numerical simulation of high velocity cloud dispersion and detonation was carried out systematically.A numerical model of the dispersion and detonation process of high speed cloud was extablished and some breakthroughs have been made in the numerical simulation of the highspeed cloud field and its detonation process.Under the ignoration of the structural responses of the broken processes of the initial barrel and the fluid,an alternative dispersion process was explored which simplied the initial fluid as discrete droplets and particles.The dispersion process of the high speed cloud of a 2 kg FAE charge with a static initial condition and the detonation processes of the two phase PO/air and Al/air mixtures in a detonation tube were simulated,and the simulating results were compared with the experimental results,which showed that the size and shape of the 2 kg FAE high speed cloud and the overpressures of the detonation processes by simulations fitted very well with the experimental data,thus the reliability of the models and solvers used in the simulation were verified.The influence of initial falling velocity of the fuel on the shape,concentration and speed of the high speed cloud was revealed.The dispersion processes of 50 kg,100 kg,250 kg and500 kg FAE clouds under different initial falling velocities were studied based on the actual strategic needs.The change of high speed shapes and sizes,concentration and particle size distributions and velocities were analyzed and discussed under different conditions.The simulating results show that under a intial static condition,the FAE high speed cloud tend to have a “disc” shape during the whole dispersion process,while under a initial dynamic condition with falling velocity,the high concentration area of the shape of a high speed cloud experience a change from an up side down “V” or an umbrella to a “V” or a “basin”,finally to a “funnel”,in the later stage of dispersion,the whole cloud is formed by two parts: the upper ellipsoid cloud and the lower “pole” shape cloud.Under different initial conditions the radial concention distribution in the high speed cloud would always become similar,which devides the cloud into three parts: the cloud center high concentration area,the near field low concentration area and the far field high concentration area.The radial boundary velocities of the high speed cloud at different initial conditions reach the peak at 10 ms,and then decay rapidly.In the axial direction,the high speed cloud boundary undergoes three stages: rapid expansion,gradual attenuation and uniform falling down of the lower boundary.The scale effect of large mass of the fuel charge on the dispersion process was revealed.Comparing with the dispersion process of the small scale 2 kg fuel,the central gas has a much more uneven propulsive force on the fuel in the dispersion of large mass fuel charge.A signifucant backflow phenomenon was discovered during the dispersion peocess of larger mass fuel charge,under the initial static condition the accumulation of fuel in the cloud center and upward jets along the central axis occurred,while the hollow in the cloud center(which was discovered in the cloud of the small scale 2 kg fuel charge under initial static condition)disappeared.The variation law of physical parameters in the high speed cloud detonation processes as time and space changes was revealed,and obtained the quantitative results of the comparison between the static cloud detonation and the high speed cloud detonation were obtained.In order to gain a better understanding of the high speed cloud detonation,the detonation processes of 250 g and 2 kg FAE cloud were studied,and the results show that the detonation process of a FAE cloud could be devided into three stages: the cloud detonation stage,the cloud edge deflagration stage and the outside field overpressure attenuation stage;with the minimum overpressure of 0.3 atm as a standard,the overpressure damage radius of the initial static 250 g FAE cloud detonation process is around 4.5 m,and the damage time is approximately 8.5 ms,and the increase of the FAE charge mass or the initial falling velocity of the charge could have a positive effect on expanding the damage area of the FAE overpressure.