弹体高速入水特性实验研究

Experimental investigations on behaviors of projectile high-speed water entry

进行了速度在35～160m/s的平头、卵形和截卵形弹体入水实验,利用高速相机记录了弹体入水和空泡扩展的详细过程,得到了3种弹体在入水初期的水中弹道轨迹和空泡形状,并比较分析了弹体头部形状对入水弹道稳定性的影响。结果表明,平头弹体在水中飞行有良好的弹道稳定性,截卵形弹体往往由于受力不均衡在入水后期发生偏转,卵形弹体则在入水前期即发生偏转。假定弹体入水过程中的阻力系数为非定值,修改了柱形弹体水中速度衰减数学预报公式,同时根据能量守恒建立了平头弹体入水的空泡形状模型,计算结果与实验结果吻合良好。

Water-entry experiments were conducted in the velocity range 35-160 m/s for the projectiles of the three different geometries including flat nose, truncated-ogival nose and ogival nose. A digital high-speed camera was used to record the detailed processes of water entry and cavity expansion and obtain the hydro-ballistic trajectories and cavity shapes in the early stages of water entry for the projectiles of the three different geometries. And the effects of the nose shapes on the hydro-ballistic stabilities were compared among the projectiles of the three different geometries. Comparisons indi- cate that the flat nose projectile has good hydro-ballistic stability in the water, the truncated-ogival nose projectile will deflect in the late stage of water entry which is resulted from the deflecting force on the projectile nose, by contrary, the ogival nose projectile will deflect in the early stage of water entry which has the worst stability. By considering the cavitation number was a velocity-dependent factor, a modified mathematical model was proposed to predict the velocity attenuation of cylindrical projectiles and a cavity dimension model was presented based on the energy conservation. The calculations are in good agreement with the experimental results.