Jet-like flows in sudden channel expansions with horizontal or sloping
bottoms are investigated. These flows occur at inflows to lakes and reservoirs
or at wastewater discharge sites. An integral analysis approach has been used.
The main objective of the study has been to develop a method by which the
dilution of inflows to lakes or reservoirs can be predicted if t.he geometry
(simplified) and inflow conditions are known. If the. diffuser angle, the
sloping angle of the bottom inflow channel aspect ratio and
inflow densimetric Froude number are given, the equations which will be
presented can be used to estimate the dilution of plunging or non-plunging
inflows. This information is needed in one-dimensional water quality models
of stratified lakes or reservoirs. The integral jet flow analysis used herein
includes a similarity hypothesis for velocity profiles, application of the
entrainment principle and consideration of bottom friction effects on
momentum. A general theoretical model is developed to predict jet centerline
velocity, width and dilution of non-buoyant turbulent jet flows over
horizontal or sloping bottoms in abruptly expanding channels. Wall effects in
gradually expanding channels are also investigated for half jets. Predictions
obtained with the theoretical model are compared with some experimental
data of jet dimensions and dilution. The model is applied to geometrically
simplified field conditions to illustrate effects of inflow channel aspect ratio,
friction and bottom slope. All of these effects are found to be significant.
As a side product a Gauss fitting method has been developed to analyze
a finite number of laboratory measurements in horizontal diffuser flows with
finite water depth.
In an Appendix purely empirical equations for the dilution of horizontal
jet-like flows through diffusers are also developed. Experimental results of
density induced plunging flows into reservoirs (negatively buoyant) and of
non-buoyant jet flows have been used.
Fang, Xing; Stefan, Heinz G..
Integral Jet Model for Flow from an Open Channel into a Shallow Lake or Reservoir.
St. Anthony Falls Hydraulic Laboratory.
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