Simulation on Whip Phenomenon of Torpedo during Oblique Water Entry

To solve the problem of inaccurate calculation of torpedo’s initial trajectory, the water entry mechanism of a torpedo is analyzed. Based on the advantage of meshless method, finite element method(FEM)/smoothed particle hydrodynamics(SPH) coupling method is used to simulate torpedo’s large attitude motion process during oblique water entry. The correctness of the simulation model is verified by the experimental data. The whip phenomenon of torpedo during oblique water entry is analyzed, and the values of low pressure under different conditions are calculated and verified by theoretical formula. Results show that when a torpedo is entering into water, the area part under the torpedo head is trend to produce low-pressure effect, resulting in large-attitude downward motion and the whip. The low pressure causing the whip phenomenon is significantly affected by the angle of attack. The low-pressure value is larger and the duration of action is longer in the negative attack angle condition, compared with those in the positive attack angle condition. Therefore, in order to more accurately analyze and design the torpedo trajectory during water entry, the effect of the low pressure is necessary to be considered.