High-speed ditching of double curvature specimens with cavitation and ventilation

TL;DR

This study experimentally investigates the hydrodynamics of high-speed water entry of double-curvature specimens resembling aircraft fuselage sections, focusing on cavitation, ventilation, and load distribution influenced by shape, speed, and angle.

Contribution

It provides new insights into how curvature and speed affect cavitation, ventilation, and hydrodynamic loads during high-speed water entry of complex-shaped specimens.

Findings

Longitudinal curvature significantly influences cavitation and ventilation.

Transverse curvature affects pressure distribution and fluid escape.

Increased speed raises loads and alters cavitation modes.

Abstract

The water entry at high horizontal speed of double-curvature specimens, reproducing the rear part of the fuselage that first gets in contact with the water during aircraft ditching, is investigated experimentally. Three shapes are analysed, representing different aircraft types. Pressure and load measurements are taken, supported by underwater high-speed visualization. The effects of different horizontal speeds, pitch angles, and curvatures are analysed, while keeping a constant vertical-to-horizontal velocity ratio. It is observed that the longitudinal curvature plays a significant role in the hydrodynamics, potentially leading to cavitation and ventilation in the rear part of the specimen at high speeds. The transverse curvature affects the pressures and loads both at the front and at the rear, since a lower transverse curvature increases the possibility of the fluid to escape from the sides. An increase in pitch angle results in an increased loading, in terms of both amplitude and distribution. Finally, an increased horizontal speed leads to higher loads at the front but also affects the cavitation and ventilation modalities at the rear. The load scaling for flat plates also applies to these specimens at the front, but the occurrence of cavitation and ventilation invalidates it at the rear. The time evolution of the cavitation region and of the wetted area are examined through advanced image processing techniques and pressure data analysis. The comparison with the geometric intersection area of the specimen with the still water surface provides further insight into the hydrodynamic phenomena during the water entry.