METHODOLOGIES TO PREDICT HYDRODYNAMIC CHARACTERISTICS OF PUSHER AND PULLER PODDED PROPULSORS IN OBLIQUE FLOWS

This paper presents the outcome of a numerical simulation based research program to evaluate the propulsive characteristics of puller and pusher podded propulsors in a straight course and at static azimuthing conditions while operating in open water. Methodologies to predict the propeller thrust and torque, and pod forces and moments in three dimensions using a Reynolds-Averaged Navier Stokes (RANS) solver at multiple azimuthing conditions and pod configurations are presented. To obtain insight into the reliability and accuracy of the results, grid and time step dependency studies are conducted for a podded propulsor in straight-ahead condition. The simulation techniques and results are first validated against measurements of a bare propeller and a podded propulsor in straight ahead condition for multiple loading scenarios and in both puller and pusher configurations. Next, simulations were carried out to model the podded propulsors in the two configurations at multiple loading conditions and at various azimuthing angles from +30° to –30° in 15° increments. The majority of the simulations are carried out using both steady state and unsteady state conditions, primarily to evaluate the effect of setup conditions on the computation time and prediction accuracy. The predicted performance characteristics of the pod unit using the unsteady RANS method were within 1% to 5% of the corresponding experimental measurements for all the loading conditions, azimuthing angles and pod configurations studied. The non-linear behaviour of the performance coefficients of the pod unit are well captured at various loading and azimuthing conditions in the predicted results. This study demonstrates that the RANS solver, with proper meshing arrangement, boundary conditions and setup techniques can predict the performance characteristics of the podded propulsor in multiple azimuthing angles, pod configurations and in the various loading conditions with a same level of accuracy as experimental results. Additionally, the velocity and pressure distributions on and around the pod-strut- propeller bodies are discussed as derived from the RANS predictions.

Hydrodynamic Interactions between Bracket and Propeller of Podded Propulsor Based on Particle Image Velocimetry Test

In this study, particle image velocimetry was used to measure the fine flow-field characteristics of an L-type podded propulsor in various working conditions. The flow-field details at different cross-sections between the propeller and the inclined bracket were compared and analyzed, allowing for more intuitive comparison of the flow-field characteristics of L-type podded propulsors. The interference mechanisms among the propeller, pod, and bracket of the L-type podded propulsors at different advance coefficients, deflection angles, and deflection directions were investigated in depth. The results of this study can serve as reference material and provide technical support for the design and practical shipbuilding application of L-type podded propulsors. Therefore, the results have theoretical significance and practical engineering value.

NUMERICAL ESTIMATION ABOUT PERFORMANCE OF CPP AND PODDED PROPULSOR ON MANY OFF-DESIGN CONDITIONS USING RANS APPROACH

On the off-design condition of CPP or podded propulsor, the angle of attack against the propeller blade or the flow interaction between propeller and pod housing is quite different from the propeller design condition. The flow around them is very complex. Hence there is the difficulty for numerical estimating. In order to verify the applicability to wide range of the off-design condition, RANS simulations were executed. The calculation range for CPP was complete two quadrant condition each at several pitch setting. Regarding podded propulsor, pull type and push one having the common propeller and housing were targeted and the range of pod steering angle were set to all 360 degrees. Hydrodynamic performance as these calculated results were compared with published experimental results including the rotational moment of changing CPP’s pitch angle or steering the pod housing. Then, it was found that there were good agreements except for the particular kind of the operating conditions.