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Pump Performance at Sump Intakes

One of the most critical aspects of sump pump design is to ensure its unhindered performance. A good design requires knowledge of the level of submergence of the pump’s suction pipe necessary to prevent the formation of vortices (submerged or free surface) near the pipe. Over the years, studies have been conducted to find out the critical submergence levels of suction pipes. If water goes beyond this submergence level it is very likely that vortices will be formed that will affect the pump’s performance mainly due to cavitation.

Schematic of vortex formation in intakes

The critical submergence level depends on the intake flow velocity, pump suction flow rates, clearances of the pipe from side and bottom walls of the tank and also the shape of the pipe intake suction bell. These parameters differ from site to site, which means each installation can have a different critical submergence. If the level of the water cannot be maintained above the critical submergence level, baffles can sometimes be used along with design changes in the suction bell to prevent the formation of vortices. With help of FLOW-3D, we are able to predict the conditions under which there would be probable formation of vortices and to evaluate the efficiency of preventive measures to prevent them.

Related links:
Watch the FLOW-3D Demo

Vortex Detection in Pump Sumps by Means of CFD (PDF)

CASE 1: Determining Vortex Formation at Pump Intake with FLOW-3D

FLOW-3D can calculate free surface flows with its TruVOF method. In the present application it was used to simulate the dynamics of both air and water. The simulation for a pump intake was set up according the experimental setup described in [1] and results were compared with the experimental results. FLOW-3D not only predicts the formation of a vortex but was used to predict the effectiveness of baffles installed in the pump intake to prevent the formation of a vortex.

FLOW-3D predicts the formation of vortices

The above comparison shows that FLOW-3D predicts the formation of vortices in the absence of a baffle and how effective the placement and size of a baffle can be in prevention of vortex formation. The animation below shows that FLOW-3D predicts the formation of vortices near the sump intake pipe.

 

CASE 2: Determining the Probable Position of Vortex Formation

This simulation, similar to the experiment done above, is about predicting the location of an air-entraining vortex. The paper used for this validation also tries to validate results from different solvers with actual results. An experimental setup was used to view and measure the location of an air-entraining vortex. Simulations were then done to see how well they might reproduce the experimental results. A similar study to validate results from different solvers with actual data was reported in [2].The first image shows the comparison between the measured location and the location predicted by FLOW-3D. It can be seen that FLOW-3D is quite accurate in predicting the location of a major air-entraining vortex.

Experimental vs simulated location of entrained air in a pump design
Left: Actual measured location of air-entrained vortex core at water. Right: Location of air-entrained vortex predicted by FLOW-3D. The plot shown for comparison is of z-vorticity.

Velocity Profile Comparison

The following images compare velocity profiles at different locations.

 
Streamlines in a FLOW-3D pump intake CFD simulation
Streamlines as seen in FLOW-3D
Velocity profile of a FLOW-3D pump intake CFD simulation
Velocity profile at section Z=220 mm

Here, a noticeable difference between the two cases is the number of vortices formed in each case. The reason for the formation of only one vortex in the latter case is that the intake/suction pipe is off center in the tank, which gives less space for the fluid to have the swirling motion that eventually gives rise to a vortex.

FLOW-3D velocity profiles at section  Y= 140 mm for pump intake design
FLOW-3D velocity profiles at section Y = 140 mm.

 


References

  1. Numerical Prediction of Air Entrainment in Pump Intakes by Shyam Shukla, Divisional Manager & J. T. Kshirsagar, Vice President at Corporate & Research & Engineering Division, Kirloskar Brothers Ltd. 
  2. CFD prediction and model experiment on suction vortices in Pump Sump by Tomoyoshi Okamura, Kyoji Kamemoto and Jun Matsui

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