Hydrodynamic Performance Analysis And Optimization Of The Counter-Rotating Shaftless Rim-Driven Thruster

In recent years,a new type of integrated motor thruster(also known as Shaftless Rim-Driven Thruster,or RDT for short)is constantly developing.In order to further improve the performance,the research group innovatively proposed a CounterRotating Shaftless Rim-Driven Thruster.It integrates the Shaftless Rim-Driven Thruster with the Contra-Rotating Propeller(CRP).So,it has the advantages of compact structure,high thrust,high efficiency,energy saving and low noise.The design concept,hydrodynamic performance and flow field characteristics of this new type of thruster are different from those of conventional propeller.In view of this,this paper studies the CFD-based simulation method of hydrodynamic performance of the Counter-Rotating Shaftless Rim-Driven Thruster,discusses the influence of blade number,pitch and speed on its performance,and puts forward its optimization approach.The main works are as follows:(1)The accuracy of the numerical simulation method is verified by the test data of conventional CRP.The results show that: the steady calculation results of Standard k-e,RNG k-e,Realizable k-e and SST k-? turbulence models are very close.When the advance coefficient is 1.1,the prediction accuracy of unsteady method based on Standard k-e turbulence model is higher than that of steady method,but it takes much more computer resources and time.The total thrust coefficient and total torque coefficient calculated by the two methods are less than 0.5% and 2% respectively,which meet the calculation requirements.The rationality of the proposed method is further demonstrated by the analysis of the independence between the computational domain and the number of grids.At the same time,the simulation method in this paper can capture the details of the flow field well,which provides conditions for the analysis of RDT’s micro-gap flow field.(2)The clearance model and no clearance model of the Counter-Rotating Shaftless Rim-Driven Thruster are established respectively,and their hydrodynamic performance is calculated.The calculated values of frictional torque of rim are compared with those of empirical formula.The results show that: the difference between the calculated value of the total torque in the front and back domains and the value of the test formula is 1.56% and 4.08% respectively,which shows the rationality of the calculation method.Although the existence of clearance has little effect on the total thrust value,it has great influence on the torque value.Therefore,the clearance should not be ignored in the RDT model.The thrust coefficient,torque coefficient and efficiency of the Counter-Rotating Shaftless Rim-Driven Thruster are higher than the single propelle of RDT,and the efficiency advantage of the former is more prominent with the increase of the advance coefficient.(3)The influence of blade number,pitch and rotational speed on Counter-Rotating Shaftless Rim-Driven Thruster is analyzed by numerical simulation method.The results show that: a)When the number of front blades is constant,the total thrust and total torque decrease with the decrease of the number of back blades,but the open water efficiency is very close,and the increase of the number of blades will improve its vibration performance;b)With the decrease of rim length,the total thrust coefficient and torque coefficient decrease first and then increase,and the efficiency increases gradually.However,the pitch change caused by the rim length change has little influence on the total thrust coefficient and the total torque coefficient;c)The total thrust coefficient and total torque coefficient increase slightly with the decrease of the length of the parallel body,and the efficiency increases first and then decreases;d)When the inlet velocity is less than about 6m/s,the performance of the thruster gradually improves with the decrease of the speed of the front and back propellers,but when the inlet velocity is more than about 6m/s,the performance of the thruster gradually decreases with the decrease of the speed of the front and back propellers.