Theoretical And Experimental Technology Study On The Hydrodynamic Performance Of L-type Podded Propulsor

L-type pod is a new type of pod propulsor developed by United States ABB company in recent years.Its bracket is far from the blade,which can improve the uniformity of the blade inflow and reduce the fluctuating force of the propeller wake.So far,there has been no study on the hydrodynamic performance of the L-type pod.In terms of the prediction method of hydrodynamic performance of pod propulsor,theoretical and experimental studies in foreign countries have an early start.Especially,in the study of model test,due to the late start in China,the corresponding test equipment is relatively deficient,almost all kinds of experiments are basically using foreign equipment,which is not commensurate with the requirements of the development of China's shipbuilding industry and the demand of the shipping market.To solve the above problems,this paper mainly includes the following four parts:(1)General pod is taken as a prototype,and only the bracket type of it is changed to make it become L-type.The open water performance of the L-type pod and the general pod was compared and analyzed by using the computational fluid dynamics(CFD)method.Some of the key problems in the process of the numerical simulation,such as control equation,viscous flow theory,the turbulence model and the setting of boundary conditions were introduced,and the feasibility of the numerical prediction method used in this paper was verified.The hydrodynamic coefficients the blade pressure,cabin pressure and flow of two type podded propulsors were compared and analyzed in detail.The results show that in condition of model parameters,hydrodynamic performance of L-type pod has certain advantage compared with general pod and bracket type has influence on the hydrodynamic performance of podded propulsor.It can provide the theoretical basis for the open water test,the performance prediction,fine flow field measurement and performance prediction.(2)Based on the RANS method and the sliding grid technique,the unsteady hydrodynamic performance of the L-type pod with a large rudder angle and oblique flow has been studied.Numerical calculation was carried out on the hydrodynamic performance of the pod in different advance coefficients,different angles and different steering direction conditions.The variation of hydrodynamic coefficient,pressure distribution and flow field of propeller and pod unit with different oblique angle and different inlet velocity are analyzed indetail.By studying,the variation law of the hydrodynamic characteristics of the L-type pod in the course of the navigation is gained.It is found that the beneficial effect of L-type pod on flow field is gradually enhancing and meanwhile the strength of parts in the anterior segment of bracket should be put emphasis on in the design of L-type pod.(3)In view of the shortage and immature of the L-type pod experimental equipment in China,a set of L-type podded propulsion device was independently developed and key technology of the experimental equipment design of L-type pod was introduced.Technical difficulties in the fine flow field measurement of podded propulsor using the particle image velocimetry(PIV)were discussed,besides,corresponding measurement methods were studied according to these.In the ship model towing tank,the open water test was carried out on the hydrodynamic performance of the L-type pod in straight forward motion and azimuthing conditions,and in view of the macroscopic force,torque and microcosmic fine flow field,hydrodynamic performance of L-type podded propulsor in different conditions was analyzed.According to action mechanism,the interactions among propeller,cabin and bracket were analyzed.Differences and variation law of hydrodynamic performance in the process of dynamic manipulation of podded propulsor with fixed angle were gained.(4)A ship equipped with two L-type pod was chosen as the research object.By using the CFD method,the numerical simulation of the naked hull resistance and the self-propulsion performance of the double L-type pod ship model were carried out,the hydrodynamic performance of cabin and propeller was compared with that in open water,and the effect of hull wake of podded propulsor was analyzed.Based on the method of scale effect correction of pod propulsor by ITTC,the extrapolation method of self-propulsion performance of double pod ship was discussed and based on it,performance prediction of double pod ship was done.Finally,the self-propulsion performance of the full scale ship was calculated,and the flow field,pressure nephogram of full scale and model scale were compared.The full scale calculation results were compared with the conversion results,which verified the reliability of the prediction method for ship with double podded propulsors.Research findings in this paper can provide data basis and technical support for autonomous design and practical application of L-type podded propulsor in China,which has some theoretical significance and practical value.