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Technology Low-Cost Computational Fluid Dynamics Modeling For Pump Stations Avoid pump station failures, protect the environment, and save money through computer simulation. By Franz Jacobsen T highlighted by tracers and animations. here are freely available open source computational The assessment of flow characteristics, such as swirl fluid dynamics (CFD) software packages, such and uneven inflow velocities, are typically assessed as per as OpenFOAM (OPEN Field Operation And the recommendations of the American National Standards Manipulation), that have been used for many Institute Hydraulic Institute (ANSI/HI) 9.8 guidelines. The years and produce results that compare favorably with recommendations of ANSI/HI are: swirl angle not greater commercial packages. In this article the CFD simulation than 5 degrees and velocity profile at of a pump station will be compared all points within 10 percent of the crosswith a physical prototype model. The sectional area averaged velocity. For comparison of results includes swirl Throughout the pump stations with four or more pumps, angle and other flow phenomena, industry, typically the ANSI/HI guidelines recommend with excellent correlation. Some of model studies. Pump stations with flows these techniques used to aid post10 percent of greater than 5,000 GPM (315 l/s) per processing and engineering analysis existing pump pump also require model testing. will be presented. Undesirable flow conditions include stations experience submerged and free-surface vortices, Why Use Modeling For substandard preswirl at the pump entrance, nonNew And Existing Pump Stations? performance or For most pump stations, standard uniform distribution of velocity, and guidelines suffice. For complex swirling flow, which can suck entrained regular failures. applications — new or refits — there air or bubbles. These adverse flow are cost-effective CFD modeling tools conditions lead to reduced pumping available that result in: head capacity, detrimental effects on • minimized maintenance costs power consumption, and increased noise and vibration, • minimized commissioning time leading to costly breakdowns and repairs. • minimized pump station failures and possible effluent ANSI/HI pump standards recommend that for physical discharge into the environment. model studies, a free surface vortex type of 3 is considered the maximum allowable, as prototype strength may be CFD modeling is especially valuable to operators, as well slightly underestimated as a result of possible scale effects. as designers. Throughout the industry, typically 10 percent of This is not an issue with CFD models, which represent the existing pump stations experience substandard performance full scale. or regular failures, and many of these pumps operate below Subsurface vortices should be eliminated from any design design capacity. Pump stoppages, which require emergency because their presence imposes fluctuating loads on the bypass measures, can incur costs of tens of thousands of impeller and the resulting low-pressure areas may cause dollars per day or more, and, in the case of wastewater cavitation, which results in damage to the pump. pump stations, may potentially incur EPA fines. These costs The configuration of pump stations is an essential aspect of can accumulate and eat away at yearly budgets. An initial pump station performance. Poor design can lead to failures. moderate investment of a CFD model can have a favorable The application of a CFD model can determine undesirable cost/benefit outcome for the operator. CFD modeling results flow conditions and recommend remedial action, such as are user-friendly and easy to visualize, with flow paths vanes and baffles, to provide a solution to eliminate the 20 wateronline.com ■ Water Online The Magazine