Investigation on free-surface vortices within a closed pump intake under different pressure conditions using stereo PIV

Abstract

This paper examines free-surface vortices and the vorticity distribution with time-dependent evolution within a closed pump intake under five pressure conditions. The location and the strength of these vortices, occurrence probability and perspective statistics, as well as vortex probability distribution are all systematically analyzed. Three cases were observed and analyzed: (a) Subcritical (Q= 19.78 m3/h), whether vortices occur or not is related closely to the pressure magnitude. (b) Critical (Q= 22.61 m3/h), evolution of vortices was significantly impacted by the pressure applied. The number of vortices increases as the absolute pressure values increase, which was fluctuating and random. (c) Supercritical (Q= 25.43 m3/h), the spatial scale of the whole measurement section is occupied by the vortex when the highest absolute values of pressure conditions are reached. Based on statistical analyses, the probability of vortex occurrence within the measurement section was obtained. The captured vortices have been qualitatively classified into different ‘vortex zones’. The Re, We and the absolute value pressures are the most important parameters influencing the existence and the number of free-surface vortices. The experiment results may provide a reference for the actual operation of closed pump intake and the design guidelines for the installations with closed pump intakes.