Experimental investigation of the hydro-elastic behaviour of flexible composite propellers in non-uniform flow at model and full scale

In this paper, new developments in the measurement technology of the hydro-elastic response of flexible composite propellers are described. The first part of this paper covers the testing of two composite propellers operating in non-uniform flow in a cavitation tunnel. The flow field was created by a wake generator mounted inside the tunnel and designed by means of computational fluid dynamics (CFD). The obtained wake field was then validated through Particle Image Velocimetry (PIV) flow measurements. The actual composite propeller tests were carried out with Digital Image Correlation (DIC) technique to measure the deflection of the flexible blades during the full propeller revolution. This paper describes both the test setup and the challenges encountered in the data processing. Besides the laboratory tests, this paper covers the full scale test measurement campaign performed for a flexible, composite propeller installed on one of the Royal Netherlands Navy‟s diving support vessels within the Greenprop project. The deformation of the propeller blades was measured optically with DIC and two underwater cameras installed on the vessel‟s rudder providing stereoscopic images of the propeller blades. Despite challenges such as the high rotational speed of the propeller, underwater visibility, cavitation, scarcity of natural light and vibrations, excellent measurement quality was achieved as the propeller blade deformations were delivered with an accuracy comparable to the tests in the laboratory. In addition, observations of the propeller cavitation pattern were collected with an outstanding image quality.