Technical Papers

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Air Bubble Resorption
(St. Anthony Falls Hydraulic Laboratory, 1949-08) Silberman, Edward
This paper describes an analysis and experiment directed at determining the laws governing the rate of solution of a gas bubble in turbulent liquid. The object of the research was to determine methods for resorbing air bubbles which have been freed from the water in a water tunnel. A basic equation governing the resorption process which has been developed and partially verified in the work is presented as Eq. (13) in the text. Useful approximate forms of this equation are given as Eqs. (14b) and (14d) in the text. The basic equation has led to several suggested methods for accomplishing resorption in water tunnel. These include: (1) a resorber method already developed at the California Institute of Technology[1]*; (2) a method in which air in solution in water would be completely replaced in the closed water tunnel circuit by another gas such as carbon dioxide; and (3) a method in which a lengthened return circuit would be combined with a fin-scale turbulence, introduced in the return circuit to hasten air bubble resorption while keeping the bubble from rising. The time required for resorption by any of these methods may be estimated from the basic equation.
Hydraulic Model Studies for Whiting Field Naval Air Station
(St. Anthony Falls Hydraulic Laboratory, 1950-01) Bowers, Charles E.
The Naval Auxiliary Air Station, Whiting Field, is to have a stormwater disposal system in which the existing pipes and terraces under and in the vicinity of the runways and building area will discharge into paved trapezoidal open channels. Many of the channels join other channels as they pass down the sides of the plateau on which the airfield is located. The grades of the main channels and of many of the lateral channels are such that water flows at supercritical velocities or at velocities greater than that of a gravity wave. The difficulties anticipated in joining two streams of water, one or more of which is flowing at supercritical velocities, led to the request for model studies of several of the channel junctions. The primary objectives in the present study include (1) the development of junction designs for specified operating conditions which would result in reasonably smooth flow downstream of the junction and (2) the determination of the necessary wall heights in the vicinity of the junction. Economic and structural considerations involved in the junction designs were considered in the final selection. Dependent upon the junction design, the discharges, velocities, and related phenomena of the flow in the vicinity of the junction, a hydraulic jump may form in one or both of the inlet channels. This may necessitate a large increase in the height of the sidewalls in the vicinity of the junction. On the other hand, if the flow passes through the junction at velocities greater than the critical, standing waves may form which have a height greatly in excess of a normal freeboard and which continue to oscillate back and forth across the channel for a considerable distance downstream from the junction before being damped by frictional forces. These standing waves necessitate higher sidewalls not only in the vicinity of the junction but for a considerable distance downstream. As available information on junctions of this type is almost nonexistent, it was necessary to resort to model studies in order to determine the flow conditions and the minimum sidewall heights. Two general types of junctions were studied. One type consists of the junction of two large channels in which the lateral and inlet main have comparable discharges. The other type, called terrace outlets, consists of a junction between a main channel and a terrace channel having a relatively small discharge. The maximum discharge ranges from 380 to 960 cfs in the main channels and from 25 to 70 cfs in the terrace channels. The maximum velocity of flow encountered is approximately 30 fps.
An Electrical Method for Measuring Air Concentration in Flowing Air-Water Mixtures
(St. Anthony Falls Hydraulic Laboratory, 1950-03) Lamb, Owen P.; Killen, John M.
An electrical instrument has been developed to measure the air concentration in flowing air-water mixtures as part of an investigation of the mechanism by which atmospheric air is entrained in flowing water. The theory, development, and verification of this instrument are described in this report. The instrument is shown in Figs. 6c and 7, and the electrical circuit is shown in Fig. 9b. The electrical measurement of air concentration was chosen after examining possible mechanical, chemical, and magnetic methods. The method consists basically of a measurement of the difference between the conductivity of a mixture of air and water and conductivity of water alone. A mechanical strut supporting a pair of electrical probes has been combined with the electrical circuit in such a manner that air-concentration measurements may be made, not at a point, but at least in a small region of the flow. With this instrument it is now possible to traverse the flow cross section both vertically and laterally and to obtain the distribution of air in the flowing mixture. The relation between the instrument readings and air-concentration values are determined theoretically and the instrument is direct reading. by checking the results of the electrical method against a direct mechanical sampling method, it has been determined that the values of air concentration computed form theoretical conditions alone were sufficiently accurate for experimental work without further calibration. The instrument is now designed for application in an experimental laboratory channel, but with the use of a more rugged strut and supporting structure the method could be applied equally well in large flumes and spillways.
Hydraulic Data Comparison of Concrete and Corrugated Metal Culvert Pipes
(St. Anthony Falls Hydraulic Laboratory, 1950-07) Straub, Lorenz G.; Morris, Henry M.
Full-scale tests were conducted at the St. Anthony Falls Hydraulic Laboratory of the University of Minnesota primarily for the purpose of obtaining pipe friction and entrance loss coefficients for concrete and corrugated metal culvert pipes, which would be more accurate and dependable than those currently recommended in culvert design literature. Comparison of these test data is presented in this paper and recommendations are given for design values of the coefficients under various flow conditions. The experimental studies were made on new culverts, all of which were installed and maintained with excellent alignment. A high degree of accuracy was possible in these tests for all of the culverts. Sizes up to 3 ft in diameter were investigated. Analytical studies were made of the data obtained from the experimental observations which were significant to basic pipe flow theory where systematic form roughness and large diameters come into consideration.
Hydraulic Tests on Corrugated Metal Culvert Pipes
(St. Anthony Falls Hydraulic Laboratory, 1950-07) Straub, Lorenz G.; Morris, Henry M.
Experimental studies on culverts conducted at the St. Anthony Falls Hydraulic Laboratory of the University of Minnesota, beginning in 1946, included several series of observations on commercial , corrugated metal culvert pipes, The primary purpose of these large-scale tests was to obtain pipe friction and entrance loss coefficients which would be more accurate and dependable than those currently recommended in culvert design literature. A previous paper in this series gives a discussion of the comparison with the results of parallel studies on concrete culverts. The present paper is confined to a discussion of the corrugated pipe culvert test program and an analysis of the results of the studies. Two types of corrugated metal culverts were tested, namely, the circular and the pipe arch types. In each case, threee different nominal diameter pipe sections were tested--18 in., 24 in., and 36 in., respectively--, making a total of six corrugated metal culverts in the test program. Each pipe was 193 ft long and laid on a slope of 0.20 per cent. For the pipe arch culverts, the identifying dimensions refer to the diameters of circular pipes having the same length of periphery. For example, the 36-in. pipe arch and the 36-in. circular culvert have equal perimeters although their heights, widths, and areas are unequal. Cross sections of the various pipes, with controlling dimensions, appear in Fig. 1. (Note that the corrugation height in each case is 1/2 in. and that all computations have been based on the inside section, that is on the minimum cross-sectional area.) Friction and entrance loss coefficients were established for the culverts under the usual conditions of field operation. With this objective in view, each pipe was tested for the following conditions: (a) Full flow with submerged inlet and outlet. (b) Part-full flow at uniform depth. For each flow condition, several values of head and discharge were used. In addition, five of the culverts were tested with two different entrance conditions; namely, (a) Pipe projecting 2 ft into the headwater pool. (b) Pipe entrance flush with headwall.
Hydraulic Tests on Concrete Culvert Pipes
(St. Anthony Falls Hydraulic Laboratory, 1950-07) Straub, Lorenz G.; Morris, Henry M.
Included in an experimental program conducted at the St. Anthony Falls Hydraulic Laboratory of the University of Minnesota on full-scale culverts was a series of tests on concrete pipes up to 3 ft in diameter. The primary purpose of these tests was to obtain pipe friction and entrance loss coefficients which would be more accurate and dependable than those currently recommended in culvert design literature. the studies were begun in 1946. This paper is confined to a discussion of the concrete culvert test program and the results of the studies. The test series included three concrete culvert pipes, 18 inches, 24 inches, and 36 inches in diameter, respectively. Each pipe was 193 ft long and laid on a slope of 0.20 per cent, except that the 24-in. pipe was on a slope of 0.224 per cent. the pipes tested were all manufactured by the cast-and-vibrated process. Details of the pipe sections are shown on page 22. Friction and entrance loss coefficients were established for the culverts under the usual conditions of field operations: (a) Full flow with submerged inlet and outlet. (b) Part-full flow at uniform depth. The 18-in. and 36-in. diameter pipes were tested for each of the two types of flow with two different entrance conditions; namely, (a) pipe projecting 2 ft into the headwater pool, (b) pipe entrance flush with the headwall. The 24-in. pipe was tested with the projecting entrance only.
Capacity of Box Inlet Drop Spillways Under Free and Submerged Flow Conditions
(St. Anthony Falls Hydraulic Laboratory, 1951-01) Blaisdell, Fred W.; Donnelly, Charles A.
The box inlet drop spillway is defined as a rectangular box open at the top and at the downstream end. The spillway is shown in Figure 1. Storm runoff is directed to the box by dikes and headwalls, enters over the upstream end and two sides, and leaves through the open downstream end. An outlet structure is attached to the downstream end of the box. The long crest of the box inlet permits large flows to pass over it with relatively low heads, yet the width of the spillway need be no greater than that of the exit channel. the drop spillway has been extensively used as a gully control structure where it is necessary to drop water from as short a distance as 2 feet to as much as 12 feet. In more recent years it has also been used in drainage ditches where it functions as a title outlet and means of dropping excess surface water into the ditch. For the sake of economy, auxiliary vegetated spillways are sometimes provided to pass part of the runoff from the larger storms and to permit the use of smaller mechanical spillway. In order to prevent scour of the drainage ditch banks the elevations of the vegetated spillways are adjusted so no water will pass over them until the downstream drainage ditch flows back full. In other words, the mechanical spillway must have sufficient capacity to fill the ditch completely before any flow passes over the vegetated spillway. Under these conditions the high downstream water level will likely submerge the spillway and reduce its flow. After the vegetated spillways come into operation, the downstream level rises still further and submergence of the mechanical spillway becomes greater. Spillways designed in this manner are known as the "island dam" type because they can be completely surrounded by water during flood periods. The necessity for these studies to determine the capacity of box inlet drop spillways under submerged flow conditions thus becomes apparent.
Hydraulic Design of the Box Inlet Drop Spillway
(St. Anthony Falls Hydraulic Laboratory, 1951-01) Blaisdell, Fred W.; Donnelly, Charles A.
This paper contains sufficient information to permit the complete hydraulic design of a box inlet drop spillway and explains briefly the various factors that influence the design. Its four major sections deal with the free flow capacity, the outlet design, the submerged flow capacity, and the utilization of the preceding information in the design of box inlet drop spillways. The box inlet drop spillway may be described as a rectangular box open at the top and at the downstream end. The spillway is shown in the Frontispiece and in Figure 1. Storm runoff is directed to the box by dikes and headwalls, enters over the upstream end and two sides, and leaves through the open downstream end. An outlet structure is attached to the downstream end of the box. The long crest of the box inlet permits large flows to pass over it with relatively low heads, yet the width of the spillway need be no greater than that of the exit channel.
Design Studies for a Closed-Jet Water Tunnel
(St. Anthony Falls Hydraulic Laboratory, 1951-08) Ripken, John F.
A variable-pressure water tunnel, which is a testing facility analogous to a wind tunnel, is a useful tool in the study of cavitation or hydrodynamic characteristics of underwater bodies. This paper includes general, selective, hydrodynamic design studies for the construction of a large closed-jet water tunnel, together with experimental model test data and design analysis of a specific selection of flow components. Each flow component is critically examined with regard to its influence on test section flow quality, cavitation, susceptibility, and energy head loss. Included are studies of the test section, contraction, diffuser, vaned elbows, and pump. Presentation in chapters devoted to single flow components simplifies the treatment and increases adaptability of the findings to conduit design problems other than water tunnels.
Hydraulics of Closed Conduit Spillways Part 1. Theory and Its Application
(St. Anthony Falls Hydraulic Laboratory, 1952-01) Blaisdell, Fred W.
The closed conduit spillway is any conduit having a closed cross section through which water is spilled. The inlet and outlet may be of any type. The barrel may be of any size or shape and may flow either full or partly full. Also, the barrel may be on any slope. This broad definition includes the smallest culvert as well as the largest morning glory spillway. The basic theory of the flow is the same for each of the many forms which the spillway may take. This paper discusses the control of the flow through closed conduit spillways by weirs, the barrel exit, tailwater, pipe, orifice, and short tube, since each of these controls may govern, at some time or other, the rate of flow through the spillway. The effect of these various controls on the performance of the spillway is explained. A means of developing a composite head-discharge curve is given. Pressures within the closed conduit spillway must sometimes be determined, so the methods for this determination are presented. A selected bibliography useful to the understanding and for the design of closed conduit spillways concludes this technical paper.
Velocity Measurement of Air-Water Mixtures
(St. Anthony Falls Hydraulic Laboratory, 1952-03) Straub, Lorenz G.; Killen, John M.; Lamb, Owen P.
A troublesome aspect of experimental studies of flow phenomena in air-water mixtures has long been that of making accurate velocity measurements. In the pas, bulk-flow measurements have been made variously with surface floats, injected dyes or salt clouds, and relationships between the discharge and depth of flow. Point measurements of velocity have been attempted by measuring stagnation pressures in the air-water mixture. These methods have not been of sufficient accuracy for many purposes. An instrument for making accurate point velocity measurements throughout a section of an aerated flow stream has been invented and developed at the St. Anthony Falls Hydraulic Laboratory. The transit time, between two fixed electrodes, of minute cloudlets of salt solution injected repetitively into the flowing air-water mixture is measured electronically. A rate of 15 injections per sec permits a direct measure of the mean flow velocity over a short stream filament. In the present form of the instrument, this mean velocity is indicated directly on a meter calibrated in feet per second. Measurements can be made in aerated flows with air concentrations exceeding 70 or 80 per cent and at very high velocities. Velocity measurements with the new velocity meter in nonaerated flows check within 1 or 2 per cent of those made with a Pitot tube. The integrated water discharge inan aerated flow stream, taking into account both the measured air distribution and the velocity distribution and making reasonable estimates of the water discharge through the boundary areas have also checked the water discharge through the boundary areas have also checked the water discharge measured directly with an accuracy of 1.5 per cent.
A Capacitive Wave Profile Recorder
(St. Anthony Falls Hydraulic Laboratory, 1952-10) Killen, John M.
Research studies at the St. Anthony Falls Hydraulic Laboratory necessitated the development of a device for measuring and recording the profile of surface waves. The initial phase of these studies involved waves with periods ranging from 1/3 to 1 sec and with heights ranging from 1/2 to 3 inches. Existing methods of measuring and recording the profiles of these waves were considered to be not entirely satisfactory. A method has been developed whereby wave heights are measured electrically with a recording oscillograph; the deflections correspond to the depths of submergence of an insulated wire into the water. This insulated wire acts as a small capacitor whose capacity varies directly with the wetted area of the wire. The system has a linear calibration. Thus, accurate and continuous wave profiles can be recorded. Hysteresis effects due to surface tension are about 0.003 ft. A sensitivity up to 1/2 cm pen deflection per O.OO1-ft variation in water level is possible. The method may be used for greater wave heights, however some adjustment in oscillator may be required in extreme instances.
Importance of Secondary Flow in Guide Vane Bends
(St. Anthony Falls Hydraulic Laboratory, 1953-01) Silberman, Edward
For purposes of analysis, the flow in a guide vane bend is divided into a basic or primary two-dimensional flow with superimposed secondary flow. The two-dimensional flow is reviewed briefly first. It is then shown from experimental data that, for practical purposes, the secondary flow has negligible influence on the two-dimensional deflection, but the two-dimensional head loss is increased materially by the secondary flow. The effect of the secondary flow on head loss can be divided into two parts. The first part causes a loss which can be measured immediately behind the vanes, while the second part causes a loss which occurs between the trailing edges of the vanes and a plane about 4 duct hydraulic diameters behind the miter line of the bend. The second part is considerably larger than the first and may be attributed to increased wall shear downstream of the vanes. The increased wall shear is, in turn, attributable to the redistribution of streamlines by the secondary flow.
Importance of Inlet Design on Culvert Capacity
(St. Anthony Falls Hydraulic Laboratory, 1953-01) Straub, Lorenz G.; Anderson, Alvin G.; Bowers, Charles E.
The design of a culvert inlet has a significant bearing upon the relationship of the head to the discharge of a culvert. Its relative importance hinges upon the type of flow occurring in the culvert, which in turn is governed by the location of the control section. For part-full flow the control may be either at the inlet or the outlet depending on whether the slope is hydraulically steep or mild. In the case of short culverts, control may be at the inlet even for horizontal or mild slopes. For full flow, barrel friction provides the control. The head-discharge curves of culverts having square-edge inlets have been compared with those for culverts having rounded inlets to illustrate the conditions for which a head-advantage may be obtained by using a rounded inlet. These comparisons have been made for three categories of culvert flow: long culverts on steep slopes, long culverts on mild slopes, and short culverts. Dimensionless head-discharge curves have been plotted for culvert flow in each category. For culverts on steep slopes, experimental data have been compared with the computed values and, since the agreement was reasonably good, serve as a basis for the analysis of flow in culverts operating under conditions other than those for which the tests were made. The greatest head-advantage for a particular discharge of the rounded inlet over that of a square-edge inlet was found for those cases in which the control section was located at the inlet. These were long culverts on steep slopes or short culverts where the length was negligible. for long culverts on mild slopes, the head-advantage was far less pronounced.
Straight Drop Spillway Stilling Basin
(St. Anthony Falls Hydraulic Laboratory, 1954-11) Donnelly, Charles A.; Blaisdell, Fred W.
This paper describes the development of the generalized design rules for a new stilling basin for use with the straight drop spillway. This generalized stilling basin design was developed because experience in the field had shown that there was no satisfactory stilling basin for the straight drop spillway. However, limited field experience indicates that this new design will adequately protect the downstream channel from scour. Water falling over the spillway crest falls onto a flat apron. The nappe is broken up by floor blocks, which also prevent damaging scour of the downstream channel banks. Scour of the downstream channel bed is prevented by an end still. Flaring wingwalls, triangular in elevation, prevent erosion of the dam fill. For proper operation of the stilling basin, the contraction of the flow at the ends of the spillway opening must be partially suppressed. The stilling basin can be used for a wide range of discharge, head on the crest, crest length, height of drop, and downstream tailwater level. An important finding is that the stilling basin length computed for the minimum tailwater levels. Dangerous scour of the downstream channel may occur if the nappe is supported sufficiently by high tailwater so that it lands beyond the end of the stilling basin. A method of computing the stilling basin length for all tailwater levels is presented. The design rules developed as a result of the laboratory tests were carefully checked an verified. An example shows how these rules are applied to the design of field structure.
The Six-Inch Water Tunnel at the St. Anthony Falls Hydraulic Laboratory and Its Experimental Use in Cavitation Design Studies
(St. Anthony Falls Hydraulic Laboratory, 1956-03) Straub, Lorenz G.; Ripken, John F; Olson, Reuben M.
A recirculating model water tunnel has been devised at the St. Anthony Hydraulic Laboratory for the purpose of determining prototype design data for use in the planning of various types of cavitation test facilities. The test section of the model is 6 in. in diameter, and various boundary geometries have been studied in their relation to the test stream flow quality. Special emphasis has been given to the cavitation test limits imposed by the test section boundaries and various other tunnel components. This paper describes the basic tunnel, the critical cavitation tests made on the tunnel, and some cavitation studies made in the tunnel. Observations made on closed (cylindrical and diverging), open, and slotted0wall test sections are discussed. A minimum cavitation index of about 0.023 can be achieved in the diverging closed-jet test section at a velocity of 50 fps. Some cavitation studies indicate how the cavitation susceptibility of the tunnel water varies, and show that the critical cavitation index of a slender body is more constant when based on a measured pressure than when based on vapor pressure.
The St. Anthony Falls Multi-Purpose Test Channel
(St. Anthony Falls Hydraulic Laboratory, 1956-07) Straub, Lorenz G.; Bowers, C. E.
In its original concept the design of the St. Anthony Falls Hydraulic Laboratory provided for a Multi-Purpose Test Channel which would be a main feature of the gravity flow research facility on the Mississippi River at the Falls. This channel has been used for many test programs and has been progressively developed for a wider range of applications since the completion of the Laboratory structure in 1938. It is now approaching its ultimate development by the installation of towing facilities which are soon to be completed.
Hydraulics of Closed Conduit Spillways Parts II through VII Results of Tests on Severa Forms of the Spillway
(St. Anthony Falls Hydraulic Laboratory, 1958-03) Blaisdell, Fred W.
The theory of the hydraulics of closed conduit spillways has been presented previously as Part I of this report series. Parts II to VI describe the laboratory tests, record the observed flow phenomena, and give the discharge and pressure coefficients necessary for the application of the theory. This information is given for five different forms of the closed conduit spillway, four of which are recommended. The drop inlet described in Part II is not recommended because of its poor hydraulic performance.
Hydraulics of Closed Conduit Spillways Part VIII. Miscellaneous Laboratory Tests Part IX. Field Tests
(St. Anthony Falls Hydraulic Laboratory, 1958-03) Blaisdell, Fred W.
The theory of the hydraulics of closed conduit spillways has been given in Part I of this report series. Parts II to VII, giving results of tests on several forms of the closed conduit spillway and discussion of vortices, have also been published. Parts VIII and IX, presented in this paper, report the results of tests on a number of additional forms of the closed conduit spillway. In contrast to the general tests reported in prior Parts, the tests reported here are model tests of specific field structures and actual field tests of full size structures. The results have been presented in such a way that they have general application to the design of the type of structure they represent.
Hydraulics of Closed Conduit Spillways Part X. The Hood Inlet
(St. Anthony Falls Hydraulic Laboratory, 1958-04) Blaisdell, Fred W.; Donnelly, Charles A.
Comprehensive experiments on the hood inlet for closed conduit spillways are reported. The capacity and performance of the spillway for variations of the hood inlet length, the conduit slope, the wall thickness and the approach conditions are described. The great effect of vortices on the spillway capacity is shown and anti-vortex devices are developed. Scour in the vicinity of the hood inlet is determined for various sizes of stone and equations for the scour hole dimensions are presented. A few special inlets were tested, the effect of rounding the entering edge being the principal variation.

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