Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
MODIFYING FACTOR AND PROPOSAL FOR A NEW CAVITATION FORECASTING DIAGRAM IN MARINE PROPELLERS
Submission Author:
Flavio Peres Amado , RJ , Brazil
Co-Authors:
Flavio Peres Amado, Arthur Moreira Estevão de Moraes , Lais Cristine Felix Carvalho
Presenter: Flavio Peres Amado
doi://10.26678/ABCM.COBEM2021.COB2021-0223
Abstract
The classic method of predicting cavitation in marine propellers through the Burril diagram has been employed for almost 80 years, being considered by researchers as a highly reliable tool for the use in the development of impellers of fixed pitch. There are also methodologies that consider the influence of hydrofoil on the performance of the component, relative to cavitation. However, previous work has questioned the reliability of such techniques for detecting low percentage cavitation, such as 2.5%. It is considered that both the experimental and numerical methods that give rise to those results are inaccurate to predict exact values of cavitation in such a small region. Thus, the authors propose in this paper a new methodology, which takes into account an angular modifying factor, symbolized as f, which focuses on the cavitation index σ07R used in the classical methods, relative to the resulting velocity in the section at 0.7R of the blades. This factor considers the dimensional characteristics of the impeller, the physical properties of the fluid where it is navigating and the pressure conditions on the component axis. It is plotted against rotational speed values, in diagrams that indicate the occurrence of cavitation directly from the reading on the graph, without the need for excessive calculations. Because of the unreliability of the various methods in detecting cavitation in a very small region of the back of the blade, the diagrams are only built for percentages from 10% onwards. The f values can be raised numerically or experimentally in tests in cavitation tunnels. However, the values of the Burril diagram itself were employed, since they are considered highly reliable for projects that support cavitation above 10%. The intention of the method is to advance the state of the art in the knowledge of the subject and offer a facilitating tool to the designer. The results of cavitation prediction achieved herein are compatible with those from the classic methods used in the marine rotor market.
Keywords
Cavitation, Burril Diagram Method, Marine Propeller
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