Study On The Hydrodynamic Performance Of Podded Propulsors

Podded propulsor is a new type of ship propulsion device developed in recent years, which offers improved hydrodynamic performance, saved space, increased payload capability and improved battle effectiveness. Therefore, it could make the advantage of electric power propulsion bring into play enough and has wide market application prospect and great military application value. In this dissertation, research was carried out on the steady hydrodynamic performances of podded propulsors with the use of numeric calculations.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 based on which the steady hydrodynamic performance of podded propulsor was calculated was built, and the FORTRAN program was completed. In this method, the hydrodynamic forces on propeller blades were calculated with the panel method that suit to lifting body, while the hydrodynamic forces on the pod and strut were calculated with the Hess-Smith method for non-lifting body. Hydrodynamic interactions between the propeller and the pod and strut were treated by iterative calculations.The open water performance of a propeller without pod was calculated at first. The numerical results agreed very well with the experimental data. Then the steady performances of the pusher types and puller types were calculated and compared with the experimental results. The distribution of induced velocity at the propeller disk caused by pod and the loading distribution on propeller blades was numerically discussed. The results show that the present method can finely predict the performance of puller type and pusher type podded propulsors. The induced velocity caused by pod and strut was calculated and the results indicated that the blockage effect is obvious on the right ahead of bracket, and it bring on additional hydrodynamic loads on the propeller of a puller or pusher type podded propulsor. Based on a type of puller podded propulsor ,one or two fin was added to the pod, then the steady hydrodynamic performances were calculated, and the results were compared with the common type, the results indicated that the performances were increased 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 were more better, it has bigger thrust and efficiency, also, the loading distribution on blade are bigger.The wake flow field caused by the pod with one and two fins were calculated, and the calculation results indicate that there is another high-wake zone on the right head of the fin beside the right head of bracket. The blockage effect is more obvious when the included angle is smaller. There are also some influences on the radial and tangential velocity caused by fin.The unsteady performance of podded propeller was calculated. The unsteady performances of podded propeller in steady flow and in stern wake field were calculated independently, and the influence of the stern was analyzed.