Experimental Research On Internal Flow Of Low Specific Speed Centrifugal Pump Based On PIV Technology

Centrifugal pump as the key power equipment for fluid transportation,in addition to superior hydraulic performance indicators,more importantly,must have good reliability in the operation process.The stability and reliability of the work is the premise to determine whether the centrifugal pump can be used.The unsteady flow in the centrifugal pump is an important factor that determines the stability of the pump.Although there are many domestic and foreign studies on the unsteady flow in the pump,there is a certain understanding of the internal flow structure and the flow law of the rotating machinery such as the water pump.However,the internal flow of the centrifugal pump is more complicated.There is no deep understanding about the mechanism of many flow phenomena and its impact on the internal and external characteristics.Therefore,in order to better explore the influence of internal flow phenomenon of centrifugal pump on the internal flow field and external characteristics,the internal flow of radial impeller with low specific speed centrifugal pump was quantitatively studied by PIV technology.The main work and research results of this paper are as follows:?1?Summarized the domestic and foreign research status of centrifugal pump PIV testing technology,internal flow and hump phenomenon.?2?A centrifugal impeller full-fluid PIV experiment test system was designed and built.The internal and external characteristics of the test pump at a speed of 1000 r/min were tested.The test results show that hump phenomenon occurs when the test pump operates at 0.5 times the best point?0.5Q_d?.?3?12 working points between 0.1Q_d and 1.2Q_d was selected and the flow field in the impeller of the test pump was studied through the PIV technology.It explores the occurrence and development process of the unstable flow structure in the impeller of the test pump.The results show that the unstable flow phenomenon begins to appear at 0.75Q_d,and two separation vortices appear in the flow channel 1 at the 0.6Q_d operating condition.As the flow rate gradually decreases,the suction side vortex moves toward the middle of the flow path inlet and the flow path,and the pressure surface side vortex moves toward the flow path outlet.?4?The influence of the unstable flow on absolute velocity in the flow channel is analyzed by extracting the absolute velocity circumferential components and the absolute velocity radial components on the five flow lines in channel 1.The results show that the absolute velocity circumferential component increases firstly and then decreases with the increase of the runner radius.The variation trend is similar under different working conditions,and the size is inversely proportional to the flow rate.The change of the radial component of the absolute velocity with the increase of the runner radius is more complex,and the size is proportional to the flow rate.?5?Under different conditions,the relative speeds on the inner arc and the outer arc in the flow channel 1 were experimentally studied.The results show that the wake area gradually increases as the flow rate decreases,and the jet-tail intensity increases with the radius of the runner increases.?6?Three points are selected at equal distances from the exit of channel 1 of the test pump,and the circumferential components of the three points non-dimensionalized absolute velocity are averaged to obtain the average non-dimensionalized circumferential components of exit absolute velocity v_u2/u₂.As the flow rate increases,the non-dimensionalized circumferential components of the exit average absolute velocity(L_Avag)curve increases firstly and then decreases.The hump phenomenon appears between 0.0 Q_d and 0.5Q_d,and the L_Avag and the head both decrease monotonically with the increase of the flow rate.between 0.5Q_d and 1.2Q_d According to the comparison between the head curve and the L_Avag curve,unstable flow is one of the factors leading to the hump phenomenon.