Reduction of Entrained Vortices in Submersible Pump Suction Lines Using Numerical Simulations

Abstract

Pump intake structure design is one area where physical models still remain as the only acceptable method that can provide reliable engineering results. Ensuring the amount of turbulence, entrained air vortices, and swirl are kept within acceptable limits requires site-specific, expensive, and time-consuming physical model studies. This study aims to investigate the viability of Computational Fluid Dynamics (CFD) as an alternative tool for pump intake design thus reducing the need for extensive physical experiments. In this study, a transient multiphase simulation of a 530 mm wide rectangular intake sump housing a 116 m3/h pump is presented. The flow conditions, vortex formation and inlet swirl are compared to an existing 1:10 reduced scaled physical model test. For the baseline test, the predicted surface and submerged vortices agreed well with those observed in the physical model. Both the physical model test and the numerical model showed that the initial geometry of the pump sump is unacceptable as per ANSI/HI 9.8 criteria. Strong type 2 to type 3 submerged vortices were observed at the floor of the pump and behind the pump. Consequently, numerical simulations of proposed sump design modification are further investigated. Two CFD models with different fillet-splitter designs are evaluated and compared based on the vortex formation and swirl. In the study, it was seen that a trident-shaped splitter design was able to prevent flow separation and vortex suppression as compared to a cross-baffle design based on ANSI/HI 9.8. CFD results for the cross-baffle design showed that backwall and floor vortices were still present and additional turbulence was observed due to the cross-flow caused by the geometry. Conversely, CFD results for the trident-shaped fillet-splitter design showed stable flow and minimized the floor and wall vortices previously observed in the first two models.

Numerical Investigation of the Performance of a Submersible Pump: Prediction of Recirculation, Vortex Formation, and Swirl Resulting from Off-Design Operating Conditions

“…For all the cases, the geometry and mesh were created using an in-house pre-processing software CADAS, and the numerical simulations were run using ANSYS Fluent. Similar approaches and methodologies with those discussed in Arocena et al [14] are used throughout this section. Grid size and element lengths for Cases 1, 2, and 3 were derived from the grid independence study conducted on Case 1 of the same publication.…”

“…Indicating that only air can pass through this boundary. At this point, it is important to highlight that the forebay for Case 1 represents the full-scale prototype for the reduced-scaled sump used in the physical model test presented in [14]. As an overview, it should be noted that for open channel flow, gravity and inertial forces play a more dominant role than viscous or turbulent shear forces.…”

“…Keeping the Froude number in both the model and the prototype constant is a good approximation of dynamic similitude [15]. As such, the 1:10 undistorted scale selected for the physical model test in [14] is based on a constant Froude number (Fr = 0.38) as computed across the suction bell for both the model and the prototype. Additionally, it was verified that the Reynolds number (Re = 1.44 × 10 5 ) across the 260 mm diameter suction bell of the model is way above the minimum criteria of 6 × 10 4 as set by ANSI/HI [1].…”

A Study Comparing the Subsurface Vortex Characteristics in Pump Sumps

“…In the study by Choi et al, the location of the vortex was predicted using CFD techniques [7]. In addition, CFD was used to analyze the swirl angle, which was used to determine the imbalance of the water returned to the pump through the bell-mouth by Ayham Amin et al [8,9]. As such, the prediction of pump sump performance using CFD techniques has been carried out effectively, but it is difficult to predict the free surface vortices and sub-surface vortices using CFD under the ASME HI 9.8 standard.…”

Hydraulic Performance of Seawater Intake System Using CFD Modeling

“…The likelihood of localized swirl and vortex formation can be reduced by placing a wall close to the intake. The liquid depth must also be sufficient to prevent surface vortices [18,19].…”