Mechanism analysis of vibration and noise for centrifugal pump working as turbine

Centrifugal pumps as turbine (PAT) are widely used in the petroleum and chemical industry with reasonable efficiency and low cost investment. And it represents the primary source of vibration and acoustic energy in industrial pipeline system. The amount of emitted energy may vary significantly between different designs and it is generally not well known. In order to better understand the flow-induced vibration and noise characteristics of centrifugal pump in reversible turbine operation, a single grade end suction centrifugal pump was chosen as research object. The fluid flows into the PAT through the outlet in pump mode and flows out through the inlet. A synchronous acquisition of performance parameters and vibration and noise signals were realized on the basis of INV3020C data acquisition system and performance test system in an open test loop. The liquid is pressurized through the booster pump, and then the high pressure liquid impacts the turbine impeller to make it rotate. The dynamometer consumes and measures the turbine's energy. The operating condition was adjusted by regulating the frequency of frequency converter to change the booster pump's capacity. Experimental studies on the vibration characteristic at different monitoring positions and acoustic characteristic at the upstream and downstream of PAT were carried out on the test bench, during which the rule and frequency characteristics of vibration and noise versus rotating speed were investigated at variable and constant flow rates. The vibration and flow noise signals were collected within 30 s using acceleration sensors and hydrophone at a sampling frequency of 20 kHz. The vibration measurements were performed on the bearing, pump casing, the inlet and outlet flange and the pump foot in horizontal and vertical directions with acceleration sensors (INV9822A). The noise was measured with flush-mounted hydrophones (ST70) located at 260 mm upstream and 400 mm downstream of PAT, which were four times of pipe diameters. The signals were amplified and recorded by INV3020C data acquisition system and FFT was used for computing the spectra with the Hanning window for reducing the spectrum leakage. Experimental results show that, with the increase of rotational speed, the head and shaft power of PAT increases, and the highest efficiency point moves to larger flow rate with wider high-efficiency range. Under a certain speed, the vibration acceleration under the same monitoring point grows with the increase of flow rates. Meanwhile, the vibration energy of PAT is focused on the high frequencies, and the vibration enhances with the increase of rotating speed. The vibration strength of volute is higher than that of other measuring points for larger flow rates. The vibration strength of each measuring point comes mainly from the horizontal direction. Under a certain speed, the sound pressure level gradually grows with the increase of flow rates. Because the noise mainly comes from the interaction of blade and tongue closer to the outlet, and the radiated noise is hindered by the casing and impeller, the sound pressure level of downstream is higher than that of upstream under the same flow rate. The total sound pressure level basically increases with the increase of rotating speed.