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The vortex formed at the pump intake is known to be the main factor affecting the performance of a pump and it contributes directly to the increase of energy consumption. This study was aimed at obtaining an in-depth visualization and identifying the characteristics of the vortices generated by the installation of a bell-shaped suction inlet in a pump-induced flow using particle image velocimetry (PIV). A complementary metal-oxide semiconductor (CMOS) camera was used to capture images of the illuminated bubbles in a sump pump model. The PIV images were analysed using PIVlab, which provided representations of the 2-D plane velocities and vorticities around the inlet of the pump. The measurements were taken at four different planes that were coaxial with the bell circumference below the bell inlet. The results showed that the diameter of the vortex structure became smaller as it approached the bell inlet. Higher values of vorticity were observed within the vortex core, which conformed to the characteristics of a vortex formation. The velocity profiles exhibited the proportionality of the velocity against the radius of the vortex, which categorized this as a forced vortex. The findings from the study will be utilized by the Department of Irrigation and Drainage (DID) Malaysia to develop remedial measures for problems related to the formation of vortices in sump pumps.

Swirling flow in pump sump intake has been the subject of discussion for the past decades due to the detrimental effects brought about by its existence. Among the effects of swirling flow are reduced pump efficiency, cavitation, excessive vibration and load imbalance at the pump impeller which are caused by hydraulic problems associated to swirling flow such as swirls and vortices. One of the remedial measures for preventing such occasion is by keeping the pump inlet submerged above a defined value known as the minimum inlet submergence. It is the minimum submergence required to reduce the probability of the occurrence of free surface vortices. However, this requirement may not be fulfilled in some situations due to on site conditions or operational restrictions. In this paper, an experimental study was conducted to investigate the characteristics of swirl angle in the pump intake flow when the pump inlet is submerged near the value of minimum inlet submergence. The ratio of pump submergence to the minimum submergence was varied between 0.8 to 1.2 with constant inlet Froude Number which referred to as submergence ratio. The strength of the swirl in the intake flow was determined by measuring the swirl angle which was accomplished using a swirl meter attached in the suction pipe. Measurements using Acoustic Doppler Velocimeter (ADV) was performed to capture the velocity profile in the intake sump. The swirl angle distribution across the range of submergence ratios was dominated by a subsurface vortex formed at the sump floor. As soon as the submergence was reduced below the minimum submergence, a free surface vortex emerged near the pump inlet and brought a swirl retardation effect to the swirl meter rotation resulting in a bigger fluctuation of the swirl meter reading. An anti vortex device (AVD) called the floor splitter commonly used to reduce vorticity at pump inlet was installed and its effect on the reduction of swirls and vortices was evaluated.

Vortex formation near the pump inlet in the sump during intake is a phenomenon that needs to be controlled to maximize the pump efficiency. In this study, five variants of an AVD type called the plate type floor splitter are installed in a single intake pump sump model to evaluate the effect of geometry of the floor splitter on the effectiveness of vortex control in the intake flow. The acceptance criteria according to ANSI HI 9.8 2012 standard are that the vortex formed in the sump must be eliminated and the swirl angle in the flow must not exceed 5°. The submergence of the inlet was varied to observe the swirl reduction effect at different water levels. All floor splitter variants employed in this study have successfully eliminated the vortex but most of them did not manage to reduce the swirl angle below 5° as required. The variants with different heights displayed significant differences in swirl angle values with higher variants produce greater swirl angle reduction. The highest floor splitter variant managed to produce a swirl angle reduction below 5°. With varying lengths, however, the swirl angle values did not differ much in each case with the installation of the floor splitter variants. The advantage of the long floor splitter is that the fluctuation of swirl angle values is minimum for all submergence depths greater than 0.9 times the minimum inlet submergence which implies that the swirl reduction effect is less affected by the change in water level. By combining the advantages of both floor splitter design variation, the optimal design of plate type floor splitter can be achieved.

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