A hydraulic model of the underground pump suction intake structure of the Calumet Pumping Station was built and tested. The pumping station is an element of the projected Chicago storm runoff collection and treatment system, to be completed within the next few years. The study was conduoted for DeLeuw, Cather and Co., Consulting Engineers and Planners, Chicago, Illinois, on behalf of the Metropolitan Sanitary District of Greater Chicago. The model was built at a scale of 1:14, mostly out of plexiglass to facilitate observation. The model included the downstream end of the Calumet Tunnel, a drop structure, two symmetrically placed ducts, a wet shaft and a suction header with three branch pipes as shown in Figs. 1 through 8. It was the objective of the hydraulic model study to identify and document (a) problems with flow separation, secondary currents and vortex formation by flow visualization, (b) air entrappment and air entrainment during filling and during pump operation, (c) piezometric heads and head losses throughout the structure, (d) accumulation and entrainment of fuel oil, resulting from accidental spills, throughout the structure (e) transport and deposition of grit throughout the structure. As a result of the initial observations made in the model, the structure was modified in two locations to improve flow characteristics and to reduce grit deposition. The observations made in the model with regard to flow patterns, air entrainment and fuel entrainment have been documented by still pictures (black and white) and color motion picture. Head losses are reported in tabular and graphical form. The performance of the structure (Design C in Fig. 10) with respect to air entrainment, fuel entrainment and head losses appears quite satisfactory. Grit deposition was largely reduced but not fully eliminated. The following specific findings and recommendations were made: At high stages, that is at the beginning of the pumping cycle, flow through the structure is at low velocity and with little flow separation occurring. At low stages, flow in the drop structure becomes highly turbulent resulting at first in entrainment of floating materials and at W.S. stages below -320 in entrainment of air into the duct. In the wet shaft, there appears to be no tendency for vortex formation or air entrainment into the suction header. Only the complete blockage of the lower portion of the bar screen caused a vortex in the wet shaft. It was recommended that three air vents be installed on the suction header at the intersection of each of the three branch pipe axis with the suction header wall. These vents will prevent air accumulation in the branch header during filling. Head losses throughout the structure were found to be small. They are summarized on pages 47 and 48. Piezometric grade lines are shown in Figs. 46, 47, and 48. A major grit deposition problem existed in the divided duct due to the large reduction in flow velocities and bed shear stresses in that part of the structure. A reduction in cross-sectional area by raising the invert by several feet resulted in a significant reduction in grit deposition. Complete elimination of grit deposition appears possible with further reductions of duct width.
|Original language||English (US)|
|State||Published - May 1977|