Study On The Influence Of Coupling Between Valve And Elbow On The Internal Flow Of Centrifugal Pump

Centrifugal pump systems are widely used in industrial production.In many systems,the inlet flow of centrifugal pumps is affected by upstream maintenance valves and bent pipelines,which increases hydraulic losses,increases pressure pulsation,decreases performance,aggravates vibration and noise of the whole pump,and deteriorates operational stability.In this paper,we conducted experiments and numerical simulations on the centrifugal pump system with bent inlet pipeline and triple eccentric butterfly valve,compared and analyzed the influence of the coupling effect of the valve and bent pipeline on the hydraulic performance and internal flow field of the centrifugal pump,and compared the influence of the shedding vortex induced by the valve plate on the downstream pipeline and the internal flow of the centrifugal pump under different arrangements.The main research contents and conclusions are as follows:The internal flow of the inlet pipeline and centrifugal pump under different installation positions of the valve in the inlet pipeline was simulated,and the hydraulic performance of the pump was analyzed.It is found that the valve will lead to lower head and efficiency of the centrifugal pump,and the closer the valve is to the pump inlet,the lower the head and efficiency;however,under low flow conditions,the downstream shedding vortex of the valve will change the original pre-spin and return flow at the pump inlet and improve the work capacity of the centrifugal pump under low flow.Design conditions,the valve installation position and the pump inlet too close,the inlet velocity distortion degree increases,in the impeller inlet easy to produce backflow.At the same time,it is found that the vortex group downstream of the valve has a similar traj ectory,and its vortex volume gradually decreases with the increase of movement distance.In view of the asymmetry of the valve plate position of the triple eccentric butterfly valve,the effect of the valve plate position change on the downstream flow field and the hydraulic performance of the centrifugal pump was studied.When the valve plate is installed vertically,by comparing the two models with the valve plate eccentric to the outside of the bend and the inside of the bend,it is found that the inlet and outlet ring volumes of the centrifugal pump change when the valve plate position is changed,and the inlet ring volume of the impeller is higher than the outside when the valve plate is eccentric to the inside of the design flow condition,resulting in a larger inlet relative liquid flow angle and leading to the phenomenon of de-flow in some flow channels.Comparing with the blade load,it is found that the blade work capacity is stronger when the valve plate is biased to the outer side;the position of the valve plate will significantly affect the pressure and velocity distribution in the downstream pipe,when the valve plate is biased to the inner side,the pressure distribution in the downstream pipe is uneven,and there is a large low pressure area at the inlet,which is more likely to occur cavitation phenomenon.Through the pressure spectrum diagram can be found from the centrifugal pump inlet to the impeller flow channel in the same characteristic frequency,the valve generated by the shedding vortex on the internal pressure of the centrifugal pump has always existed.When the valve plate is arranged horizontally,compared with the valve plate upward and downward deviation of the two cases,the valve plate upward deviation,the impeller inlet relative liquid flow angle change amplitude is greater than the valve plate downward deviation,the pump inlet flow pattern is poor,the flow velocity distribution is not uniform,resulting in uneven flow distribution of each flow channel,after the valve plate produces a large number of vortex affect the inlet pipe flow field distribution,the pump inlet relative velocity increases,the vane is impacted by the incoming flow affects the ability to do work.Under the design conditions,the vortex produced when the valve plate downward deviation in the same distance in the inlet pipe faster development,the impact on the impeller inlet is weaker than the valve plate upward deviation,the pressure spectrum reflects the valve plate upward deviation,the pressure frequency components in the flow channel more rich,centrifugal pumps in the low frequency water pressure pulsation more serious.At the same time,by comparing the pressure distribution of typical impeller cross-section under four types of valve plate arrangement,it is found that the pressure field distribution of the impeller is relatively more uniform under the arrangement of the valve plate installed vertically with its bias to the outside of the bend,which is more conducive to the stable operation of the centrifugal pump.