Verdantas (formerly Alden Research Laboratory) conducted computational fluid dynamics (CFD) and physical hydraulic modeling to support upgrades to the Cedar Creek Effluent Pump Station for the Nassau County Department of Public Works. The upgrades were part of the Bay Park Conveyance Project, which diverts treated effluent from the Bay Park Sewage Treatment Plant for discharge through the Cedar Creek ocean outfall. The upgraded station included five vertical pumps and was designed to operate across total station flows ranging from approximately 47 to 150 million gallons per day (MGD).  

Verdantas first used a three-dimensional CFD model to compare geometric design modifications and help identify promising configurations for acceptable hydraulic performance. CFD was paired with physical modeling because complex, unsteady vortex behavior at pump intakes requires physical testing to demonstrate compliance with Hydraulic Institute ANSI/HI 9.8-2018 acceptance criteria.  

A 1:5.55-scale physical hydraulic model was then constructed at Verdantas' Holden, Massachusetts facility to evaluate approach flow, surface and subsurface vortex activity, swirl, and velocity distribution under a range of operating conditions. The model reproduced the chlorine contact channels, gated entrances, wet well, and pump intake geometry that could influence hydraulic conditions approaching the pumps.  

Baseline testing identified high-velocity jets and circulation within the wet well, along with unacceptable vortex activity and pump swirl. Average swirl reached as high as 34.7 degrees, compared with the Hydraulic Institute criterion of less than 5 degrees for normal operating conditions. Verdantas used the modeling results to develop and evaluate modifications that would improve hydraulic performance while minimizing construction within the existing wet well.  

The final design incorporated a vaned vortex-suppression basket with integral floor grating and an internal cruciform at each pump. Testing demonstrated that the solution effectively disrupted problematic surface and subsurface vortices and substantially reduced pump swirl. With the final configuration, average swirl ranged from 0.1 to 4.1 degrees, and all ten tested operating conditions met the Hydraulic Institute acceptance criteria. Velocity distributions at the pumps also met applicable criteria.  

By combining CFD with physical hydraulic modeling, Verdantas helped identify potential performance issues before implementation, efficiently evaluate design modifications, and develop a final configuration designed to provide satisfactory hydraulic conditions across the pump station's operating range. 

Project Highlights

• 3D CFD modeling to compare design modifications and support hydraulic design development  
• 1:5.55-scale physical hydraulic model testing 
• Evaluation of flows ranging from approximately 47 to 150 MGD 
• Analysis of approach flow, surface and subsurface vortices, pump swirl, and velocity distribution  
• Development and testing of vortex-suppression baskets and flow-straightening cruciforms  
• Reduction in average pump swirl from a baseline maximum of 34.7 degrees to a final range of 0.1 to 4.1 degrees 
• Final design met Hydraulic Institute ANSI/HI 9.8-2018 acceptance criteria for all tested operating conditions