CFD Predictions Of Open Water And Cavitation Performances Of Marine Propellers

Nowadays propellers are widely used in the field of ship propulsion. Wake generated from a ship hull has influences on hydrodynamic performances of propellers and cause propellers to vibrate. To improve vibration and cavitation performances of a propeller running in a non-uniform wake, blades of the propeller are usually of some skew angles or higher skew angles. Skewed propellers designed from different theories are required to carry out tests or theoretical calculations to evaluate whether performances of propellers meet specifications.This thesis employs the method called as Computational Fluid Dynamics(CFD) to numerically study performances of skewed propellers including open water and cavitation characteristics. This is completed by means of solving governing equations for turbulent flows of viscous fluids. By comparison with experimental data, numerical results are evaluated in terms of reliability and accuracy for different turbulence models. Results will provide useful information for theoretical study and applications in engineering.With respect to predictions of open water performances of propellers, the MAU4-50 propeller is first selected. The two-equation k-εmodel is employed. Computation results of thrust,torque coefficients and efficiency are in good agreement with experimental data. The relative errors of thrust and torque coefficients are 3.85% and 6.15% respectively. Based on this result, open water performances of a highly skewed propeller are simulated. Influences of the size of unstructured mesh area and different turbulence models on simulation results are investigated and analyzed. Relative errors for thrust and torque coefficients obtained from three turbulence models i.e. k-ε, SST and Reynolds Stress Models are within 10% for main working conditions. Among the three models, the Reynolds Stress Models give the least errors. In addition, effects of skew parameters on open water performances of propellers are further studied.For cavitation performances of propellers under a non-uniform wake, to explore accuracy of the full cavitation and Z-G-B models, cavitating flows over a two-dimensional hydrofoil is investigated first using these two models. By modifying some empirical coefficients, simulation results are satisfactory. Subsequently, cavitating flows of a skewed propeller under a non-uniform wake is simulated using modified the Z-G-B model. Results show that the positions of cavity occurrence and collapse agree well with experimental data. Four different skewed propellers are obtained by modifying skew angles. Cavitation and vibration performances of these four propellers are then evaluated. At last, influences of skew parameters on cavitation and vibration performances of propellers are found and analyzed.