Surge prediction in a gas-liquid mixed-flow pump based on multifractal detrended fluctuation analysis

Abstract

Surge causes a sudden drop in pressure increase and possibly results in severe vibration in a multiphase pump once inlet gas volume fraction (IGVF) exceeds a critical value. In this study, a synchronous test system including a high-speed camera, a laser Doppler vibrometer and high-frequency pressure fluctuation sensors is constructed to measure shaft vibration and pressure fluctuation in a gas–liquid mixed-flow pump at different IGVFs. The multifractal characteristics of the collected signals obtained by using the multifractal detrended fluctuation analysis method have been analysed and compared in detail. Results show that pressure surge occurs once the flow pattern transforms from bubbly flow to gas pocket flow in the pump. The multifractal characteristics of the vibration and pressure fluctuations depend strongly on the IGVF. Before the surge, the multifractal strength of vibration and pressure fluctuation increase with the increment of IGVF. After the surge, they decrease rapidly as the bubble coalescence into a mass of gas pockets. Furthermore, the local fluctuation of the vibration is insensitive to the variation of the IGVF and the multifractal spectrum has a right tail at each IGVF. The local fluctuation of the pressure fluctuation become severe with the coalescence of bubbles and the multifractal spectrum has a left tail after the surge. The incipient surge state can be effectively predicted by characteristics parameters extracted from the multifractal spectrum of the shaft vibration and the pressure fluctuation in the pump. This study provides an effective method for surge state prediction in multiphase pumps.