A Study on CFD-based Manoeuvring Performance Analysis of Ships equipped with Azimuth Thrusters

With the increasing use of azimuth thrusters in LNG bunkering vessels, concerns have arisen regarding the influence of duct side area variation on manoeuvring performance. In practice, simplified stock azimuth thruster models without geometric similarity are widely adopted in model tests, yet the resulting uncertainties in the assessed manoeuvrability remain unclear, and free-running model test results are often accepted without any validation procedure. In this study, free-running CFD simulations were performed using STAR-CCM+ by varying the duct side area from –5% to +15% relative to that of the original azimuth thruster. Because a one-to-one comparison of the time histories with the model test was not feasible, the CFD results were compared with the model test in terms of the zig-zag overshoot angles to examine the usefulness of the CFD approach. The results show that the duct side area significantly affects the manoeuvrability of the vessel: a smaller duct side area increased the overshoot angle, whereas a larger area generated greater lateral force during thruster vectoring, resulting in a faster yaw response and reduced overshoot angles by up to approximately 25.9%. These findings indicate that even small variations in duct side area can lead to noticeable differences in manoeuvrability, and that free-running CFD analysis can serve as a useful tool for validating simplified stock azimuth thruster models.