Browsing by Author "Johnson, Thomas R."

Now showing 1 - 6 of 6
  • Thumbnail Image
    Item
    Effluent Sampling Location and Duration Study for the Metropolitan Wastewater Treatment Plant
    (St. Anthony Falls Hydraulic Laboratory, 1987-06) Stefan, Heinz G.; Johnson, Thomas R.
    Point sampling in a non-homogenous (incompletely mixed) flow poses questions of "representativeness" of sampling requirements and optimum sampling. Such questions arise for placement and operation of monitoring stations.
  • Thumbnail Image
    Item
    Experimental Study of a Novel, Jet Booster Pump
    (St. Anthony Falls Laboratory, 1985-12) Wetzel, Joseph M.; Johnson, Thomas R.; Bintz, David W.
    A new form of a low head, jet booster pump was evaluated. The jet pump consisted of a constant diameter pipe fitted with two wall jets energizing the flow and a constant area diffuser consisting of a slotted wall portion of the pipe where water and solid fines were withdrawn. The withdrawn water was pressurized and recirculated to the j~ts by an external centrifugal slurry pump, thus performing a pressure 1 booster operation on the main line flow. The jet pump was evaluated in a 3 inch pipe recirculating flow facility. Extensive tests were conducted with water flow to evaluate and optimize performance characteristics. The best efficiency obtained was about 17 percent. Addition of solid particles to the flow in sizes up to 3/4 inch resulted in plugging of the screened diffuser for concentrations above about 20 percent by weight. Coal particles were rapidly eroded to very small sizes due to the action of the high velocity side jets. Problems associated with the screened diffuser limit the pumps' usefulness.
  • Thumbnail Image
    Item
  • Thumbnail Image
    Item
    Experimental study of density induced plunging flow into reservoirs and costal regions
    (1998-10) Johnson, Thomas R.; Stefan, Heinz G.
    The inflow entering a lake or reservoir is probably not precisely of the same density as the lake or reservoir. If the density of the inflow is less than the receiving water, the inflow will float on the surface. If the density of the inflow is greater than that of the receiving water, the inflow sinks below the surface, forming a density current. This phenomenon is referred to as "plunging" and the location where the inflow dives below the surface as the "plunge point" or "plunge line." The plunging phenomenon can be defined as the transition from open channel flow to a stratified underflow. Information is available on underflows (Ashida and Egashira, 1977; Ellison and Turner, 1959; Turner, 1973) but does not include the plunging process itself. The plunging flow can entrain some of the ambient water, thus changing the character of the inflow itself. In Minnesota plunging flow can occur in the late summer and fall when lakes are still warm from the heat absorbed in the summer and the inflowing streams are cool. It also occurs after cold weather spells in midsummer. Plunging flow can also occur if the excess density of the inflow is produced by suspended material or dissolved substances. The plunging phenomenon is not fully understood even when the receiving water is of uniform density. The situation becomes more complex when a plunging flow enters a stratified lake or reservoir where the plunging flow will entrain ambient water of increasing density as it sinks. Not only will the rate of dilution determine to which depth the underflow will sink in a stratified reservoir, lake or impoundment (Elder and Wunderlich, 1972), but it is a parameter which controls the location of the plunge line. One-dimensional unsteady water quality models require knowledge of plunging flow to be able to predict into which layer in a stratified lake or reservoir an inflow will enter. Akiyama and Stefan (1987) and Farrell and Stefan (1986) provide literature reviews of previous work on plunging flows. Akiyama and Stefan (1987) list previous studies indicating that the dilution rate of plunging flows ranges from 0 to 500% in field studies and 0 to 200% in laboratory studies. These reviews, however, indicate that most of the previous experimental and analytical work dealt with sloping parallel sided (two-dimensional) or unconfined sloping configurations. Akiyama and Stefan (1987) conducted experiments and developed an integral type analysis of plunging in a mildly diverging horizontal channel.Farrell and Stefan (1986) used numerical analysis to solve the entire flow field driven by a plunging flow in a 2-D reservoir. The geometrical configurations modeled were either mildly diverging horizontal channels or parallel sided sloping channels, which lend themselves to two-dimensional analysis. Negatively buoyant flow in a strongly diverging channel where the inflow separates from the sidewalls has not been the subject of laboratory or analytical studies, probably due to the three-dimensional nature of the flow field. In order to provide information on plunging flow an experimental study dealing primarily with strongly diverging channels (Fig. 1-1) was conducted at St. Anthony Falls Hydraulic Laboratory_ This type of flow can be related to previous analytical and experimental studies which deal with diffuser flow, jet flow, and stratified flow. Previous work done in these three subject areas will be related to the experimental results presented in the body of this study. In addition, a set of field measurements will be reported and related to laboratory experimental results.
  • Thumbnail Image
    Item
    Hydro-aesthetic improvement of St. Anthony Falls spillway at low flow
    (1986-08) Stefan, Heinz G.; Ellis, Christopher R.; Johnson, Thomas R.
    The possible expansion of hydropower development at St. Anthony Falls on the Mississippi River within the City of Minneapolis is likely to generate questions on the future appearance of the St. Anthony Falls spillway when most of the riverflow is routed through the existing powerplant and a projected additional power station. In particular, it may be asked how the aesthetics of the St. Anthony Falls spillway can be enhanced when only a small (minimum) flow is discharged over the spillway. It is anticipated that minimum flow spillway discharge will occur for 10 months in an average year when the proposed hydropower facility becomes operational. To study this particular question, an experimental study was conducted at St. Anthony Falls Hydraulic Laboratory and small flow deflectors which can be attached to the spillway surface and generate a "roostertail-like" spray were devised to make the appearance of the spillway more pleasing. The methods used in the study and the recommended design modifications are described in this report. It was not the intent of this study to determine what the minimum flow over the spillway should be, but rather to determine the best aesthetic effects on the spillway that can be accomplished at a low flow.
  • Thumbnail Image
    Item
    Multiple Point Effluent Sampling at the Metropolitan Wastewater Treatment Plant, St. Paul, Minnesota
    (St. Anthony Falls Laboratory, 1987-07) Johnson, Thomas R.; Stefan, Heinz G.
    The concentration time series measured in a sectional model of the Metropolitan Wastewater Treatment Plant (WWTP) dechlorination basin was coupled with field measurements to predict the benefits of mUltiple transverse sampling points. The measured time series was used to generate synthetic time series representing the composite samples from two, three and four sampling points located in a cross section transverse to the flow. The analysis of this data indicates how much the multiple sampling points integrqte transverse gradients, decrease the necessary time to obtain a "representative" sample and decrease the deviation of a 1 second grab sample from a true mean value.