Hydrodynamic properties of propellers with large blade-area ratio and truncated blade in free water

In the literature exist data about the hydrodynamic characteristics of propulsion systems, which include a duct and a fixed-pitch propeller with a truncated blade shape (Kaplan propeller), which has a relatively small blade-area ratio of 0.55. Usual such propellers has a very high loading coefficient, which entails the need to increase propellers blade-area ratio in order to prevent the occurrence of developed cavitation. The article presents the results of the first stage of research, which included testing a series of four-blade truncated propellers with a blade-area ratio 1.0 in free water. The tests were carried out in the towing tank of Admiral Makarov State University of Maritime and Inland Shipping on experimental installation, which include a special hydrodynamic stand. A series of tested propellers were 3D printed from PET-G plastic. A preliminary assessment showed that the chosen diameter of the models will ensure the achievement of supercritical Reynolds numbers at a rotation frequency of about 20 s^–1. However, during the tests, it was found that the rotational speed must be increased to 30 s^–1, which, in turn, led to a reduction in the test program due to the regime limitations of the experimental equipment. Nevertheless, the analysis of the test results made it possible to build a “hull” and “machinary” diagrams according to the Papmel form. An assessment of the strength of the models was carried out, which showed that the stresses arising in the root of the blade are significantly less than the allowable ones. The obtained results expand the design possibilities of Kaplan propellers with water-jet propulsion units, as well as a part of the “propeller-nozzle” propulsion complex.

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