The study on the scaling effects in the surface piercing propeller

Abstract

Surface Piercing Propellers (SPPs) are widely used in high-speed crafts. These types of propellers can work at high rotational speeds and in a turbulent environment with high efficiency. One of the most widely used methods in estimating the performance of conventional marine propellers is the use of model testing in towing tank or cavitation tunnel. These propellers' open water hydrodynamic performance can be checked in a laboratory test before being made at full scale. According to the lack of similarity between the model and the full scale in this type of propeller, the flow regime is not the same as the scale values of the model, which leads to the difference in the hydrodynamic characteristics estimate. Many scaling techniques have been created to correct the measured thrust and torque values in model scale for conventional propellers. But, SPPs operate in two different phases, and traditional scaling approaches may not be applied to these types of propellers. For this purpose, four scales of a 5-bladed SPP with available experimental data were investigated using RANS equations and applying the VOF function to the free surface. The sliding mesh technique and the K-omega turbulence model are used in grid discretization and calculation of the Reynolds stress. The numerical method was validated by the cavitation tunnel test, and the effects of scale checked by numerical estimates and conventional methods. The results of scale effects indicate that traditional approaches are unsuitable for SPPs. In detail, an examination of the pressure and shear components of the hydrodynamic coefficients shows that they are affected by the pressure component induced by ventilation pattern. Finally, the thrust, torque coefficient, and efficiency were studied by changing the Different variables and presented the results.