Numerical Prediction Analysis Of Propeller Exciting Force For Surface Ship

As propellers produce periodically varying exciting forces in the three-way non-uniform wake field at the stern, which significantly increase the underwater noise and vibration of the hull, people show great concern about the variation pattern and prediction method of propeller exciting force. Nevertheless,the complex coupling between the propeller and blade rudder working at the stern has challenged both theoretical calculation and test measurement. As such, with the CFD numerical calculation method becoming more mature, predicting and analyzing propeller exciting force at the stern using numerical processes is doubtless an effective method.In our study, a KCS ship and a KP505 propeller are used as main study objects. A numerical pool model is established on FLUENT software. Numerical prediction analysis of propeller exciting force considering free surface is performed for model and full-scale KCS Hull-Propeller-Rudder system by employing RANS method and VOF model. In order to obtain the variation pattern of propeller exciting in different oblique flow angle,the calculation of exciting force for model-scale DTMB4679 propeller and KCS Hull-Propeller-Rudder system in oblique flow is conducted at the same time.In order to validate the accuracy of calculation method used in this paper, first, check for WP03 propeller open water and cavitation performance is carried out. Next, KCS ship self-propulsion test is computed. The results showed good agreement between calculated value and experimental value. Prediction precision can satisfy the requirement of hydrodynamic calculation. Transient two-phase flow calculation is conducted on the model hull-propeller-rudder system under self-propulsion to obtain the propeller unsteady bearing force and fluctuating pressure time domain data, and exciting force frequency spectrum characteristics is analyzed by Fast Fourier Transform.As the oblique flow is seen as relatively simple non-uniform flow, to explore the general rule of propeller exciting force in oblique flow, unsteady hydrodynamic performance is computed for DTMB4679 propeller. The observation is conducted focusing on the blade surface pressure distribution and the change of single blade force. Then the influence rule of advance coefficient and oblique flow angle in exciting force is summed up. And on this basis,further prediction of propeller exciting force for hull-propeller-rudder system is carried out.The results showed that hull resistance, lateral force and sway moment coefficient increased with the increase of drift angle, and both the fluctuating peak of thrust torque and hull surface pressure with drift angle were greater than direct sailing condition whether it is in BPF or 2BPF.In order to explore the influence of scale effect on exciting force, first, full-scale simulation is carried out under self-propulsion to determine the self-propulsion point of the ship. Next, flow field around the ship and propeller exciting force is calculated and compared with the calculation results of the model. It is discovered that the wake of full-scale ship is more nonuniform,which will lead to greater exciting force than model. It is suggested that a certain allowance should be set aside when we design the propeller on the basis of model experimental results.