Performance improvement of surface piercing propeller at low advance coefficients by aeration

Surface piercing propeller (SPP) is a type of super-cavitating propellers which with ventilation on the blades have suitable performance at water-air interface. These propellers provide perfect ventilation behind the blade, which effectively controls cavitation/aeriation and improves trust performance at operational condition. Even if at high speeds the SPPs have higher efficiency compared to the conventional propellers and water jets, the main challenge is their lower efficiency than other propulsion systems, at a lower speed which can affects the starting phase of high-speed crafts. In fact, there is a lack of research in studies on these propellers which concern the improvement of their performance at low speed. In the present studies, an aeration mechanism is investigated so that air is injected upstream in order to improve performance of the propeller. The design of the experiment (DOE) is carried out on a SPP model to perform performance tests in open water conditions using the SPP flow loop mechanism at Hydrotech (Institute of Applied Hydrodynamics and Marine Technologies, Iran University of Science and Technology). The effects of the horizontal distances (alpha) and vertical distances (beta) between the ventilation point and the location of the propeller are presented in the form of non-dimensional ventilation immersion ratios beta/alpha. For different propeller immersion ratios, ventilation immersion ratios and advance coefficients, the thrust coefficient for different cases was measured and compared to unventilated conditions. The achievements of the present research are different performance curves about thrust coefficient which illustrate a good correlation between propeller performance and aeration at different propeller immersion ratios. The maximum thrust coefficient improvement is around 100% which can achieve at I = 0.25, beta/alpha = 0.05 and J = 0.4. As propeller immersion ratio I increases, region with improved performance shifts towards higher values of advance coefficient J.

Automated summary

Surface piercing propellers with ventilation on the blades provide better control of cavitation/aeriation and improved thrust performance at operational conditions. There is a lack of research on improving their performance at low speeds, but the present study shows that adjusting the ventilation immersion ratios and advance coefficients can lead to significant improvements in thrust coefficient.