Design And Hydrodynamic Performance Simulation Of Integrative Energy-saving Propulsion System

The integrative energy-saving propulsion system is a new developing propulsion systemwhose energy saving capacity is based on optimizing the interaction between the vessel’spropeller and rudder. The leading edge of the rudder is twisted and a fairing hubcap guides thepropeller slipstream around an individually designed rudder bulb, the bulb is fixed to therudder blade and turns together with the rudder. The rudder is also equipped with a flap,ensuring superb maneuvering characteristics with only relatively small steering angles neededto keep the vessel on course. By rational refitting the rudder of integrative energy-savingpropulsion system, it can produces better hydrodynamic performance and cavitation behavior.The integrative energy-saving propulsion system was designed based on panel method. Theinfluence of rudder-ball geometric parameter to propulsion system performance and designpurpose of twist rudder to its specific method were analyzed. And appearance differences oftwist rudder designed based on both potential flow theory and viscous flow theory was alsodiscussed. The flap of rudder was designed based on effect of tail-chord ratio and rotatingangle ratio to rudder normal force. Unsteady hydrodynamic performance simulation methodresearch of the system was also carried out using panel method. The energy saving andcavitation behavior were calculated using viscous flow CFD technology.In order to investigate the influence of rudderball to propulsive system, hydrodynamicperformance of propeller-rudder-rudderball system was calculated based on panel method andthe program was compiled using FORTRAN. Interaction between propeller and rudder wasconsidered by iteration. The unsteady problem was transformed into steady calculation bycircumferentially-averaged induced velocity between propeller and rudder. Comparisonresults between calculation and experiment were used to validate veracity of the program.Variable metric computation of rudderball geometric parameter was carried out, and theresults showed that the optimum matching point between rudderball diameter and propellerdiameter that made the propeller efficiency maximum. For rudderball length, theenergy-saving effect improved obviously when the length is less than its critical value. For themodel used in the paper, the energy-saving effect can reach3.23%.For velocity magnitude and direction is different along rudder span for propeller induced velocity on rudder, the rudder section is twisted to increase extra thrust or minish cavitationon rudder. The defects of traditional design method was improved, and results comparisonbetween twist rudder and original rudder showed that the hydrodynamic performanceimproved1%-2%for increase extra thrust rudder and the pressure uniformly distributed onrudder surface and the cavitation aera minished. At the same time, the accuracy of velocitydistribution on wake flow field outside the defined wake was discussed and compared withresults calculated by viscous flow method. The velocity distribution behind propeller bladeswere uniform based on both method and the difference existed mainly behind the hub. Whenthe rudderball was fixed on rudder, the distinction can be ignored.In order to investigate the influence of flap to maneuverability of integrativeenergy-saving propulsion system, the effect of tail-chord ratio and swing angle to rudderhydrodynamic performance was discussed, and then the size of flap was chosen according torudder lift and drag curves. Hydrodynamic performance of the system with fixed swing angleratio flap rudder or fixed loof rudder ratio was predicted. The results showed that for fixedswing angle ratio rudder, the propeller loading and rudder effect is positive related, and forflap rudder whose tail-chord ratiobs=0.2, the normal force ratio improved80%whenk=3/4.Based on potential theory, a new method for predicting unsteady performance ofintegrative energy-saving propulsion system had been developed. Panel method integralequations of two lifting bodies were derived, and numerical solution was also given. Propellerand rudder were solved at the same time. The interactions between them were considered byinfluence coefficients in time domain. Results of steady calculation were as initial values ofunsteady calculation. The time effects of leak vortex were also considered in unsteadycomputation. Hydrodynamic performance of the propulsion system in uniform andnon-uniform flow was calculated using integrated method. Results of steady calculation werecompared with experimental values. It can be concluded that the results anastomosis well withexperimental data and the method which is good at precision can be used in predicting thepropulsion system performances. The periods of thrust and torque are the same as propellerblades. The rudder force vibrates obviously while propeller rotates.In order to analyze the effect of viscous force to integrative energy-saving propulsionsystem, FLUENT was used to predict hydrodynamic performance and cavitation phenomenon of the system. The computational domain was separated into two sub-domains, and a rotatereference system was fixed on the propeller which rotated with the propeller while a staticreference system was fixed on the out domain. Information between two domains wastransmitted by interface. Hexahedral elements were used in both domains. Mesh is localrefined at root, tip, leading edge, following edge of propeller blade, and the wake field nearrudder. Pressure distribution of original propeller-rudder system was compared with that onthe integrative energy-saving propulsion system. It can be concluded that by redesigningrudder, the efficiency of integrative energy-saving propulsion system can improve5%-8%.The full cavitation model was used to predict the steady cavitation performance on2-Dhydrofoil and3-D propeller; the calculation results were contrasted to experimental data toevaluate its reliability. The results shows that, the cavitation model is good at predictingbeginning location of the cavity while not so good at the collaspe place. The thickness onblade is equally distributed, while it grows on blade tip. The rudder cavitation performance ofthe integrative energy-saving propulsion system was also investigate, and it shows that thepressure distribution is much more equally distributed and the area of cavity is minishedcompared with original propeller-rudder system.