Research On Operation Characteristics Of Hubless Pump-jet Thruster

Hubless pump-jet thruster is a relatively new way of boat propulsion.At present,the operation characteristics of hubless pump-jet thruster is a research hotspot in the field of ship propulsion,especially the noise characteristics have become the focus of attention.In this paper,taking a hubless pump-jet thruster as an example,the operation characteristics of the hubless pump-jet thruster are studied by means of experimental test and numerical simulation,focusing on the variation of the flow pressure pulsation of the main excitation source of the hubless pump-jet thruster noise,and the effects of working conditions and main blade parameters on the pressure pulsation in the hubless pump-jet thruster are analyzed.The main research work and achievements of this paper are as follows:1.The research progress and achievements of boat thruster development,pump thruster design theory,test and numerical simulation are introduced in detail,and the deficiency and development trend of the hubless pump-jet thruster are pointed out.2.A synchronous test-bed for multi-field performance of the hubless pump-jet thruster is set up,and the operation characteristics of model pump-jet under different working conditions(0.6Q_d～1.2Q_d)and different rotational speeds(900r/min,1200r/min and 1450r/min)are tested,and the changes of external characteristics and vibration characteristics with flow rate and rotational speed are analyzed.The test results show that:(1)With the increase of flow rate,the injection head and power of the model pump-jet gradually decrease,and the efficiency increases at first and then decreases;under different working conditions,the main frequency of the vibration velocity of the inlet and outlet of the model pump is in the axial frequency,and the vibration at the outlet is larger than that at the inlet.(2)With the increase of rotational speed,the head and power of the model pump-jet increase gradually,and the highest efficiency point shifts to the large flow rate at low speed.At different rotational speeds,the main frequency of the inlet and outlet vibration velocity is in the axial frequency,and the amplitude of the main frequency of the vibration velocity increases obviously with the increase of the rotational speed.(3)The head and power of the model pump-jet basically meet the similarity law of the pump.3.The Reynolds time-averaged equation and RNG k-εturbulence model are used to simulate the flow of the model pump-jet under different operating conditions(0.6Q_d～1.2Q_d)at 1450r/min speed,with emphasis on the influence of working conditions on the unsteady pressure pulsation of the model pump-jet.The numerical simulation results show that:(1)With the increase of the flow,the injection thrust of the model pump-jet decreases gradually,the pressure in the flow field decreases,and the velocity and turbulent kinetic energy increase(2)The main frequency of the pressure pulsation induced by the flow in the impeller rim and the impeller middle is the axial frequency,and the main frequency of the pressure pulsation in the impeller inlet and outlet center is slightly lower than the axial frequency.The pressure pulsation in the field of the model pump-jet is small under design condition4.The influence of blade parameters on the operation characteristics such as the blade placement angle(-4°,-2°,0°,+2°and+4°),blade number(5,6 and 7)and hub diameter ratio(0.20,0.23 and 0.25)on the pressure pulsation of hubless pump-jet thruster were studied by numerical simulation.The results show that:(1)With the increase of the blade placement angle,the thrust of the model pump-jet increases gradually,the pressure on the working face and back of the blade decreases,and the pressure pulsation at the inlet and outlet flange and the middle part of the impeller increases slightly.(2)With the increase of the number of blades,the thrust of the model pump-jet increases gradually,and the pressure distribution on the blade surface tends to be uniform.The pressure pulsation in the impeller generally shows a downward trend,and the amplitude at the main frequency of the pressure pulsation in the flow field decreases.(3)With the increase of the hub diameter ratio,the thrust of the model pump-jet decreases slightly,the pressure on the working face of the blade increases and the pressure on the back of the blade decreases,the pressure pulsation at the inlet and outlet edge of the impeller changes little,the pressure pulsation in the middle increases gradually,and the pressure pulsation at the center decreases slightly.