Study On Unsteady Cavitation Characteristics Of Condensate Pump

The condensate pump is the key equipment in Marine equipment and energy field.The cavitation and other unstable flow phenomena of the condensate pump pose a threat to the efficient and safe and stable operation of the equipment and system.It can lead to the decline of its own hydraulic performance,increase the vibration and noise of the fluid flow of the device,and reduce the service life of the equipment.Therefore,the study on the cavitation characteristics of the condensate pump has important academic significance and practical engineering value.Firstly,this paper takes condensate pump as the research object.The numerical simulation of different working conditions was carried out by steady numerical simulation.Research findings:under the design condition,the static pressure in the condensate pump gradually increases from the center of the impeller to the outlet of the volute,the pressure gradient changes obviously and is evenly distributed,and the flow inside the condensate pump is stable.Under the off design condition,the flow pattern inside the condensate pump is disordered.In the case of low flow rate,backflow vortex is generated in the impeller runner near the volute tongue.The smaller the flow rate,the more obvious the backflow vortex is,resulting in fluid flow disorder in the condensate pump.Under the condition of large flow rate,the fluid flow rate increases gradually with the increase of the velocity,and the higher velocity is near the outlet of the blade and the septum tongue.Then,Unsteady numerical simulation was used to study the cavitation characteristics of the condensate pump under low flow condition,design condition and large flow condition.The cavitation distribution in cascade section,the shape of cavitation in impeller and the load distribution on blade surface were analyzed under different NPSHa.Research findings:under design conditions.The cavitation allowance of the condensate pump is NPSHa=4.28 m.There are tiny cavitation on the suction surface of the blade and it is attached to the head of the blade near the back cover of the impeller.During the development of cavitation,the cavitation moves towards the front cover of the impeller and extends into the flow channel,causing obstruction to more drainage areas.The critical cavitation margin of the condensate pump NPSHa=0.91 m,and the volume length of the bubble above the suction surface of the blade accounts for 1/3 to 1/2 of the chord length of the blade.When the head of the condensate pump drops sharply in severe cavitation,it is because the cavitation adheres to the pressure surface of the blade,which changes the pressure curve and reduces the work done.Under deviating condition,the blade inlet Angle of impact increases.Since the inlet side of the blade has a strong shear force on the main flow,the condensate pump is more prone to cavitation.The primary cavitation margin is optimized under design conditions.The critical cavitation margin increases with the increase of the condensate pump flow.In the low flow condition,cavitation has little effect on the extrusion of the condensate pump and has little effect on its performance.Under the condition of large flow rate,the fluid velocity in the condensate pump is relatively larger,which leads to the increase of instability in the pump.Finally,the pressure pulsation signal of the condensate pump is analyzed.Research findings: Under three working conditions,the flow channel fluid flows stably at the inlet of the condensate pump.The amplitude of pressure pulsation coefficient increases gradually from the inlet to the outlet of the flow channel,but the amplitude is low,and cavitation has little influence on the inlet flow channel.In the impeller of the condensate pump,the amplitude of the pressure pulsation coefficient of suction surface and working face increases gradually along the flow path.Cavitation flow causes obvious fluctuation of pressure pulsation in the impeller,which is mainly manifested in the suction surface of the blade.When there is no cavitation and cavitation,the main frequency is axial frequency,and the secondary frequency is multiple number axis frequency.In the volute of the condensate pump,the amplitude of the pressure pulsation coefficient decreases first and then increases along the volute runner.The pressure pulsation amplitude is the largest at the tongue,and the flow stability is the strongest at the fifth section of the volute.When there is no cavitation and cavitation,the main frequency is mostly blade frequency,and the secondary frequency is mostly shaft frequency.When deviating from the design condition,the cavitation flow has a great influence on the pressure pulsation inside the volute.