Document Type : Original Article
Sea-Based Energy Research Group, Babol Noshirvani University of Technology, Babol, Iran
Surface piercing propellers are special supercavitation propellers operating at free surface. These propellers are designed to have the best performance at the highest speed. The geometric parameters of the number of blades and the pitch ratio will significantly impact the critical advance coefficient range, ventilation and consequently the hydrodynamic performance of the propeller. Therefore, in this paper, the effect of two crucial parameters of pitch ratio and number of blades were experimentally studied in free surface water tunnel. After calibration and evaluation of uncertainty, two 5-bladed propellers with same section profile and pitch ratio of 1.5 and 1.4 used to investigate effect of pitch ratio. The results of two 5-blade and 6-blade propellers with same section profile and pitch ratio of 1.4 were compared. The immersion ratio was 40%, and the shaft inclination angle was zero. Results showed that increasing the pitch ratio increased the thrust and torque coefficients by 30%; while increasing the critical advance coefficient. Consequently that has led to the development of a full ventilation range and improved hydrodynamic performance of the propeller. In addition, by increasing the number of blades, at values greater than the critical advance coefficient, the thrust and torque coefficients were increased by 10%. However, the critical advanced coefficient changes were negligible. Comparing the results in the three-dimensional contours showed that with the change in the number of blades, by increasing the pitch ratio, the critical advance coefficient increased; which led to a further increase in efficiency.