Effect of fin size and angle of attack on the structural evolution of cavity and flow field characteristics on high-speed horizontal water entry of a large-caliber vehicle

To investigate cavity evolution and hydrodynamic forces of a large-caliber vehicle with fins during high-speed horizontal water entry, an experimental platform was established. The cavity evolution process was captured by high-speed photography. On this basis, detached-eddy simulation was employed to analyze cavity evolution and hydrodynamic forces. The effects of fin size and angle of attack (AOA) on flow field characteristics were also systematically examined. Results show that horizontal water entry of a vehicle at a nonzero AOA exhibits periodic tail-slapping accompanied by cavity deformation at each slap position. The cavity exhibits three distinct patterns: (1) the front section shows a regular tail-slapping cavity; (2) the middle section displays necking phenomena with a rough surface, linked to Kelvin–Helmholtz instability; (3) the rear section collapses into dispersed bubble clusters dominated by Rayleigh–Taylor instability. Analysis of the coupled relationship between pressure and turbulent kinetic energy, from the perspective of energy conservation and transformation, reveals the mechanisms of cavity collapse and recovery. Moreover, larger fins increase tail-slapping frequency, resulting in greater cavity deformation. When the mean aerodynamic chord doubles, the lateral acceleration (ay) increases by more than 100%. Increasing AOA promotes the integration of small-scale vortex blobs into large-scale vortex tubes, with the vortex core volume expanding due to the amplified tail-slapping motion. When AOA = 3° increases to 9°, the ay increases to approximately 8 times the original value.