Numéro : 2719 - Year : 2017
Toward taking into account the ventilation for the propeller design
Pol MULLER, Camille YVIN, DCNS Research/SIREHNA (Nantes - France)
Civilian and military vessels, whether fast, offshore or with a low draft, can see their propulsive performance degraded by the appearance of the ventilation phenomenon on the thrusters. This phenomenon consists in the suction of the free surface in the disk of the propeller which is then only partially immersed and no longer works in a conventional regime. The consequences are initially visible on propulsive performance by a sudden drop in thrust and torque, but also on the noise, vibrations and fatigue of the propulsion line, since this phenomenon is very unsteady and causes sudden variations of the engine speed. These unsteady forces can cause significant mechanical damage.
This paper presents a numerical study of the phenomenon of ventilation based on model test results of a thruster model with varying operating points and constant immersion. The immersion is sufficiently small for the ventilation phenomenon to be clearly developed in tests, without being present at all operating points. Several operating modes can be distinguished: subcritical (no ventilation), critical (inception and early ventilation) and supercritical (fully developed ventilation).