Numerical Simulation Of Propulsion And Cavitation Performance Of Podded Propulsor

Podded propulsor is a new type of ship propulsion device, it's suspended under the ship and it's not only a propulsive device but also a steering gear, as a result, the traditional shafting and rudder is abandoned. Podded propulsor offers improved hydrodynamic performance, saved space and can improve the mobility of ship design and manufacture. There is prominent development on maneuverability, reliability, efficiency of ship driven by electric power propulsion because of the appearance of Podded propulsor. Podded propulsor can be used in more and more field and has wide market application prospect in the new century. Based on potential flow theory and CFD technology, research was carried out on the propulsion and cavitation performance, and the wake model of podded propulsor was studied.Based on potential flow theory, surface panel method was proposed for predicting the steady hydrodynamic performances of puller type and pusher type podded propulsors, the theory model of the steady hydrodynamic performance of podded propulsor was built, and the FORTRAN program was completed. In this method, the hydrodynamic forces on propeller blades and strut were calculated with the panel method that suit to lifting body, hydrodynamic interactions between the propeller and the pod and strut were treated by iterative calculations. The distribution of induced velocity at the propeller disk caused by pod and the loading distribution on propeller blades were analyzed. The calculation results indicate that the present method can finely predict the performance of puller and pusher type podded propulsor. There is a strong wake area in front of the pod and strut. The hydrodynamic load of propeller will increase because of the blockage effection of pod and strut.Podded propulsor wake model is changed because of the interference between pod, strut and propeller, so the empirical wake model is not applicable, and then a new wake model was proposed in order to improve the precision of the calculation method. The trailing vortex of propeller was divided into two parts, the near wake and far wake. In near region, radius of wake was determined by flow conservation, and the pitch of the wake trailing was determined by aligning the vortex line with streamline. The radius and pitch of far regions was constant and the value was equal to the ending value of the near regions. The deflexion angle of strut wake was determined by the front velocity of strut, and the angle was renewed through each iteration calculation until the hydrodynamic performance was convergent. The results indicate that the precision of new wake model is better than that of old wake model, and the applicability of this new wake model is good.Based on a puller type podded propulsor, one or two fins were added to the pod, then the steady hydrodynamic performances were calculated in order to study the feasibility of using additional device to podded propulsor, and the results were compared with the performance of common type podded propulsor. The results indicate that the performances are better no matter the pod with one fin or two fins. From the comparison between the pod with one fin and two fins, we can obtain that the podded propulsor with two fins are more better because it has bigger thrust and efficiency, also, the loading distribution on blade are bigger. The increment of the propeller performance is small, and this indicates that the additional thrust of fin can reduce the resistance of pod.The numeric method of unsteady performance of podded propulsor was investigated. Based on integral solution method, the interference of propeller and pod was considered by the change of influence coefficient caused by their relative motion. The results of new method were compared with results of velocity iteration method and CFD method to verify the applicability of this method. The hydrodynamic performances of podded propulsor in uniform and non-uniform inflow were calculated. The results show that integral solution method can finely predict the steady and unsteady performance of podded propulsor. Thrust and torque of the blade will increase obviously while it rotates through the strong wake field areas, and the unsteady forces and moments of the propeller consist of blade frequency components mainly because of the effect of wake.Steady and unsteady performances of podded propulsor were investigated based on FLUENT in order to analyze the influence of azimuth angles and established angles. FORTRAN associate with Gambit were used to build calculation model of podded propulsor. The hydrodynamic performance of podded propeulsor in uniform flow was calculated by moving mesh technology. The variation of axial force, side force, vertical force and torque of podded propulsor were analyzed. The flow field of podded propulsor and the influence of pod on the flow field were analyzed. The performance of a puller type podded propulsor at different azimuth angles and established angles were calaulated, and the influence of azimuth angle and established angle on hydrodynamic performance were analyzed.The unsteady boundary element method was used to calculate the cavitation performance of a puller type podded propulsor. The string iterative process method was adopted to calculate the dimension and shape of blade cavitation. The cavitation performance of three-dimensional wing and propeller in open water were calculated to certify the accuracy of the program, and the unsteady cavitation performance of podded propulsor in uniform flow was calculated. The variation of cavitation dimension at different position was analyzed.