LES investigation on cavitating flow structures and loads of water-exiting submerged vehicles using a uniform filter of octree-based grids

Abstract

The water-exit course of a submerged vehicle launched underwater that moves into the atmosphere is one of the most important considerations in naval applications. In the present work, a large-eddy simulation with a uniform filter of an octree-based isotropic mesh and a high-resolution interface-capturing algorithm is employed to investigate this issue, with a special emphasis on the flow structures and pressure features. Various launch parameters, including the immersion depth, navigation speed, and angle of attack are discussed. The flow structures sensitive to adverse pressure relevant to the water-exit angle are captured and discussed. The flow experiences a laminar-turbulent transition and forms coherent turbulence structures, which develop a series of primary and secondary hairpin vortices. The distribution of pressure is more monotonic and regular on the pressure side of the vehicle as the angle increases, while a propagation of disturbance and a transition to turbulence can occur across the lateral side. Based on the clearly captured evolution of the water surface and cavitation, the cavity shedding induced by a pinch-off effect of the travelling liquid-vapor contact lines is found and investigated. The structural features of turbulence are greatly affected in this case, which contrasts with the noncavitating features. The structures are tuned due to the existence of cavitation, which blocks the hairpin-vortex generation mechanism. The cavity surface is full of Tollmien-Schlichting wave-like vortical structures caused by liquid-vapor interface shearing. Hundreds of monitors are intensively arranged on the vehicle's surface to capture the transient pressure signals, through which the crucial pressure features induced by the growth and collapse of the cavitation are captured.