Sammendrag
The hydroelastic behavior of propellers has been a recurring topic in ship propulsion; seen at
time as a possible cause for failures of propulsive systems and some other times as an opportunity
for improving the performances of propellers as a noise and vibration sources, it often suffered
from a lack of experimental material to validate design and analysis codes. There are, as a matter
of facts, very stringent limitations on what can be done in experiments on propeller models
in hydrodynamic facilities. These limitations arise both from the scaling laws the experiments
abide to and from the difficulties in producing flexible, with controlled mechanical properties,
propeller blades. However, the progresses in computer simulations of fluids and structures allow
for another strategy to be sought. In fact, it is possible to use the numerical simulations as a link
between the model scale experiments, where the test conditions can be accurately controlled,
and the full scale products, which is where hydroelasticity ultimately matters.
In this paper we present the results from a series of tests carried out on three homogeneous
and isotropic flexible propeller blade sets. The three propellers are variations of the same geometry,
where the original blade skew distribution was altered. The blades were produced both
in aluminum and in a epoxy-like resin, through the technique of resin casting. The aluminum
blades served to make the form for the resin blades, assuring a geometric correspondence, and
also as a reference as rigid blades since their elasticity can be neglected in model scale. The tests were carried out in SINTEF Ocean’s large towing tank in open water condition, i.e the inflow
to the propeller was uniformly distributed. The tests were performed at different propeller
rotational speeds and at different pitch settings. In order to establish a reference condition for
the flexible propellers, all the tested conditions were also run with the rigid blades; this way, it
was possible to quantify the significance of the different Reynolds number at which the blades
were tested. It is worth pointing out that the terms rigid and flexible are used here to refer to
the blades made of aluminum and resin respectively; in fact, albeit also the aluminum blades are
strictly speaking flexible, their stiffness in model scale makes any deformations under the effect
of hydrodynamic loads too small to be observable; on the contrary, the resin blades clearly show
deformation when loaded that can be measured by the laboratory equipment.
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