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
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.
Stefan, Heinz; Wood, Addison.
Calumet Pumping Station Hydraulic Model Study.
St. Anthony Falls Hydraulic Laboratory.
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