Hydrodynamic Propulsion
Introduction
In designing and constructing a high-speed boat, one of the most important steps is the selection of a propulsion system and a suitable propeller. At present, Sea-Based Energy Research Group focuses on the surface-driven system with semi-immersed propellers. The purpose of research in this field is to achieve the most suitable thrust system for high-speed boats with the most suitable hydrodynamic coefficients.
Different tools and methods are used to achieve this goal. Part of these steps is experimental testing of constructed models in the free surface cavitation tunnel, and the second part consists of performing semi-experimental solutions and numerical simulations for obtaining hydrodynamic coefficients, developing the propeller design algorithm and validating with experimental experiments.
The free surface cavitation tunnel and experimental testing equipment are fully explained in the equipment section.
Objectives of Propeller Design
1. Generation of required thrust
2. Low torque and high efficiency
3. No cavitation
4. High Solidity
Semi-Immersed Propellers
Semi-immersed propeller are a special type of super-cavitation propellers that operate in semi-immersed conditions. These types of propellers are designed to deliver the best performance and maximum efficiency at the highest speed. The benefits of semi-immersed propellers have led to the use of these types of propellers for most of high-speed boats.
The most important parameters affecting the behavior of the semi-immersed propellers are geometric features such as number of blades, Pitch ration, extended area ratio, angle of inclination, skew angle, propeller section area, as well as physical properties, such as vertical angle of the shaft, shaft transverse angle, advanced ratio, immersion ratio and Reynolds, cavitation, Weber, and Froud Numbers.
Experimental Methods and Model Testing
Different methods such as numerical solutions, empirical experiments, semi-experimental relations, etc., are available to calculate hydrodynamic coefficients. Due to the problems of modeling and numerical solutions, sometimes empirical data has been used. Due to the lack of testing facilities for semi-immersed propellers in Iran, the research group has been designed and constructed a free surface cavitation tunnel for the first time in Iran.
The required propellers are constructed after selecting the desired parameters and scaling, and will be installed at the section of the cavitation tunnel and will be tested at the specified conditions. Finally, using the Labview software, the outputs are obtained as thrust and torque coefficients.
Numerical and Semi-Experimental Methods
Alongside the empirical experiments, numerical and semi-experimental methods are very effective in reducing the quantity of experiments and in cost saving of constructing various propellers. Numerous simulations are used in many applications. These include the CFX and Fluent hydrodynamic softwares. In addition to the hydrodynamic discussions, the strength of propellers is also one of the topics discussed. In structural solutions, Abaqus software can be used. In semi-experimental solutions, it has been attempted to collect the experimental data from a regression relationship to achieve hydrodynamic coefficients and to develop a suitable thrust system selection algorithm.
