Pressure pulsation and vibration characteristics of large cube-type pump device under different working conditions

Abstract: In order to study the characteristics of pressure pulsation and vibration under the different operation conditions, four pressure pulsation sensors on the inflow part and two vibration sensors on the top of the box were arranged to measure the pressure pulsation characteristics and vibration characteristics in this paper. The pressure pulsation and vibration characteristics of the axial flow pump inlet part under the different conditions were revealed. The model pump impeller diameter was 0.3 m, the speed was 1 150 r/min, the design flow rate was 253 L/s, the design head was 1.16 m, and the nD value was 345. The model test was divided into three parts: 1）the pressure pulsation test of five flow condition points (126, 153, 203, 253, and 285 L/s) based on the entire submerged state of the outflow passage and non-cavitation state of the axial-flow blade; 2) the open flow pressure pulsation test of four flow condition points (153, 203, 253, and 285 L/s) by controlling the pressure of the water tank to ensure the water level was 30 cm from the top of the outflow passage; 3) pressure pulsation test of four flow condition points (153, 203, 253, and 285 L/s) under the cavitation condition. The pulsating pressure under the condition of cavitation was determined based on the 1% drop in efficiency of the pump device. The experimental results showed that the pressure pulsation peak value of the impeller chamber inlet was larger. This was because the inlet of the impeller was mainly affected by the positive and negative pressure. A large low-pressure zone was formed on the suction surface of the blade and a high-pressure zone was formed on the pressure surface of the blade, resulting in the large velocity gradient and pressure gradient. The pressure gradient showed a large pressure pulsation at the inlet of the impeller. In the case of small flow conditions, the pressure pulsation amplitude was greater than the designed condition and the large flow conditions. In order to ensure the safe and stable operation of the pump station and reduce the vibration and noise of the unit, operation in the small flow area for a long-time should be avoided. The main frequency of the impeller chamber monitoring points equaled to the blade frequency. In addition to the low frequency pulsation of the inlet flare tube, the main frequency was mainly distributed in the position of leaf frequency and rotation frequency. The pressure fluctuation on the impeller chamber inlet was symmetrical, but not symmetrical on both sides of the inlet flare tube. This was due to the incomplete symmetry of the flow in the same section. The pressure pulsation peak value in the impeller chamber decreased with the increase of the flow rate. In the non-cavitation conditions, the unit's hydraulic vibration was the only vibration caused by the fluid's basic pressure pulsation. Under the open and the cavitation conditions, compared with the absence of cavitation, the law of the frequency distribution was basically anastomotic and the main frequency value was larger. The vertical vibration value was smaller than the horizontal vibration value. The horizontal vibration displacement was within 10 μm and the vertical vibration displacement was larger, indicating that the vertical vibration of the pump device was more obvious. Under cavitation conditions, the vibration displacement increased by 2.4-8.6 μm compared with non-cavitation, and the smaller the flow rate, the greater increase of vertical vibration displacement. Therefore, in the application projects, operation in the cavitation conditions should be avoided as much as possible. The experiment on the inlet pressure pulsation of the tank-type pump device can provide the reference for the optimization design of the similar pump system. At the same time, it can provide guidance for safe and stable operation of tank-type pumping stations.