Research at the St. Anthony Falls Laboratory (SAFL) is continually in flux - with over fifteen affiliated faculty and SAFL's talented applied engineering group, new projects and experiments are always coming in the door, utilizing our unique facilities, expertise, and/or experimental spaces. Learn more below about an ongoing applied project that looks to improve flow metering in sanitary sewers.
Long-throated flumes (LTFs) have been used extensively in measuring irrigation flows worldwide, but to date have seen little documented use in sanitary sewers. A project sponsored by the Metropolitan Council Environmental Services (MCES) looks to investigate the application of round-bottomed LTFs, also known as a U-flumes, to sanitary sewers. A LTF with a U-shaped throat is one of the many custom flumes that can be designed using the WinFlume software, and are well suited for metering flow in the circular, gravity flow pipes that are used in sanitary sewers. A primary goal of this project is to validate the accuracy of the Winflume software specifically for U-flumes.
In the initial project phase, a 1:2 physical model of a U-flume design was built at the St. Anthony Falls Laboratory (SAFL) on the model floor (see banner image above). It was laid out using SAFL’s overhead data carriage system, which is capable of 3-dimensional positioning with a resolution of 1 mm. The flume throat, contraction and expansion sections were fabricated from high-density foam coated with epoxy to achieve the specific curved geometry, and topped with vertical acrylic windows. The top was left open to allow water surface scans using the overhead data carriage. To generate an experimental rating curve for the flume, a series of ten different flow rates were run through the U-flume model, using the SAFL flow measurement capabilities (orifice plates, weigh tanks) to measure each flow with an accuracy of 1%, along with the associated water levels in the flume. The water level downstream of the flume was also varied at each flow rate, to assess the ability of the flume to handle backwatering.
Simultaneously, a high-fidelity 3D computational fluid dynamics (CFD) analysis (>7 million nodes) was run with the same geometry using VSL3D software, a CFD code also developed at SAFL (see image to right). VSL3D features second order accuracy, incorporation of Curvilinear Immersed Boundaries (CURVIB) method; and highly scalable parallel code that can employ up to 10,000 CPU’s. For this study, Large Eddy Simulation (LES) was employed to simulate turbulent flow, combined with the level set method for modeling the water free surface. The CFD model gives the ability to, for example, model the effect of non-ideal upstream conditions on the accuracy of a metering flume.
The rating curve (head vs. flow rate) determined from the physical and CFD models were compared to a rating curve predicted by the WinFlume model. Preliminary results suggest that WinFlume does a reasonable job predicting the rating curves, operational limits, and associated uncertainties of U-flumes. Furthermore, VSL3D accurately represented the flow dynamics of the flume, and thus CFD modeling of two metro area metering sites is now underway, which includes analysis of several alternative designs.
William Herb, SAFL Research Associate
Matthew Hernick, SAFL Research Associate
This project commenced in Summer 2016 and will be completed Fall 2019.
Project ongoing - no report available.