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A WATER RESOURCES TECHNICAL PUBLICATION

ENGINEERING MONOGRAPH NO. 33 BUFCCATI OF P1..?1,1!13

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Hydraulic Design of Transitions for Small Canals

UNITED STATES DEPARTMENT

OF THE INTERIOR

BUREAU OF RECLAMATION!

A WATER RESOURCES TECHNICAL PUBLICATION

Engineering Monograph No. 33

Hydraulic Design of Transitions for Small Canals

By W. P. SIMMONS, Jr.

Division of Research

Office of Chief Engineer, Denver, Colorado

United States Department of the Interior • Stewart L. Udall, Secretary

BUREAU OF RECLAMATION

Floyd E. Dominy, Commissioner

B. P. Bellport, Chief Engineer

In its assigned function as the Nation's principal natural resource agency, the Department of the Interior bears a special obligation to assure that our expendable resources are conserved, that renewable resources are managed to produce optimum yields, and that all re-sources contribute their full measure to the progress, prosperity, and security of America, now and in the future.

ENGINEERING MONOGRAPHS are published in limited editions for the technical staff of the Bureau of Reclamation and interested technical circles in Government and private agencies. Their purpose is to record developments, innovations, and progress in the engineering and scientific techniques and practices that are employed in the planning, design, construction, and opera-tion of Reclamation structures and equipment.

First Printing: April 1964

UNITED STATES GOVERNMENT PRINTING OFFICE

WASHINGTON: 1964

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C., 20402, or the Chief Engineer, Bureau of Reclamation, Attention 841, Denver Federal Center, Denver, Colo., 80225. Price 35 cents

Preiace

THIS MONOGRAPH is the Bureau of Reclamation's first progress report on methods used and results obtained in determining energy losses and flow characteristics of transitions for moderate and small size canals. The transitions are used to connect pipelines to canals and canals to pipelines. The testing techniques and the conclusions reached in evaluating variables affecting erosion, or scour, in canals adjacent to the transitions are also de-scribed. The research studies discussed are part of the Bureau's program of hydraulic research directed toward the development of more efficient and economical designs for water conveyance structures.

The monograph was prepared in the Office of the Chief Engineer, Denver, Colo. It is based on information originally reported in the Bureau's Hydraulics Branch Laboratory Report No. Hyd-

492, "Progress Report 1—Research Studies or Inlet and Outlet Transitions for Small Canals,' dated July 31, 1962. The author of the mono-graph presented the paper "Inlet and Outlet Transitions for Canals and Culverts" at the Twelfth Annual Hydraulics Division Conference of the American Society of Civil Engineers, a University Park, Pa., August 6-9, 1963. Th paper embraces essentially the same informatio contained in the laboratory report.

The results achieved through the studies de scribed in this monograph were obtained by the close cooperation between the staffs of the Canals Branch, Division of Design, and the Hydraulics Branch, Division of Research. The data werq compiled over a period of several years. Manyt engineers assisted in the performance of the testo and in analyzing the data obtained.

Contents Page

Preface

Introduction

Test Equipment 3

Investigation 15

Open-Channel Transitions 15 Closed-Conduit Transitions—Air Model Tests 23 Combination Closed-Conduit and Open-Channel Transitions 29 Closed-Conduit Transitions—Hydraulic Tests 30 12- by 28-inch Transition 30 12- by 24-inch Transition 31 Square Inlet on 12- by 24-inch Transition 36

Conclusions 37

LIST OF FIGURES Number Page

1. Typical field installation of a broken-back transition. Siphon out-let at station 521, West Lateral, Rogue River Basin project, Oreg 1

2. Schematic views of test facilities 4

3. Hydraulic model and instrumentation 5

4. Broken-back transitions and flow-spreading hump 6

5. Flow conditions and scour. Outlet flow, broken-back transition modified with warped surfaces, 1 to 8 slope, 6-inch rise 7

6. Velocity distributions and loss factors, 12- by 28-inch closed-conduit transition, horizontal pipeline 8

7. Velocity distributions and loss factors, 12- by 24-inch closed-conduit transition, horizontal pipeline 9

8. Velocity distributions and loss factors, 12- by 24-inch closed-conduit transition, with divider pier, horizontal pipeline 10

vi CONTENTS

Number Page

9. Air model facilities for testing closed-conduit transitions 11 10. Closed-conduit transitions tested on air modeL. 12 11. Wall pressures on closed-conduit transitions used as outlets. Ap-

proach pipe 6.2 D long. Air model tests 13 12. Flow conditions and scour patterns, outlet flows, broken-back

transition, 1 to 8 slope, 6-inch rise, inlet pipe horizontal 16 13. Flow conditions and scour patterns, outlet flows, broken-back

transition, 1 to 8 slope, 12-inch rise, inlet pipe horizontal_ _ _ _ 17 14. Flow conditions and scour pattern, outlet flows, broken-back

transition, 1 to 8 slope, 12-inch rise, inlet pipe on 2 to 1 slope_ 18 15. Flow conditions and scour pattern, outlet flows, 30° broken-back

transition, 4-inch rise, inlet pipe horizontal 18 16. Flow conditions and scour pattern, outlet flows, 25° broken-back

transition, 4-inch rise, inlet pipe horizontal 19 17. Flow conditions and scour pattern, outlet flows, 25° broken-back

transition, 4-inch rise, inlet pipe on 2 to 1 slope 19 18. Scour patterns, outlet flows, 20° broken-back transition, 4-inch

rise, 20-inch canal invert 20 19. Flow and scour in canal protected by 4-inch layer of 1M-inch gravel,

1 to 8 slope, 6-inch rise transition with warped walls and horizontal pipeline, outlet flows 21

20. Table of operating conditions and performance characteristics of transitions 22

21. Effect of submergence on loss coefficients—N1=0.71, f.p.s 23

22. Flow conditions and scour patterns, outlet flows, combination closed-conduit and broken-back transition with floor deflector, 1 to 5.5 slope, 12-inch rise, inlet pipe horizontal 24

23. Velocity distribution for closed-conduit transitions used as outlets, approach pipe 6.2 D long. Air model tests 25

24. Velocity distribution for closed-conduit transitions used as outlets, approach pipe 20.4 D long. Air model tests 26

25. Draft head at inlet and loss coefficients for closed-conduit transitions used as outlets. Air model tests 27

26. Area curves for constant height, circular-to-rectangular transitions and for conic transitions 27

27. Combination transition using closed-conduit and open-channel broken-back section, with and without humps 28

28. Flow conditions and scour pattern, outlet flows, combination closed-conduit and broken-back transition, 1 to 5.5 slope, 12-inch rise, inlet pipe horizontal 29

29. Scour patterns, outlet flows, combination closed-conduit and broken-back transition, 1 to 5.5 slope, 12-inch rise, inlet pipe on 2 to 1 slope 30

30. Flow conditions and scour pattern, outlet flows, combination closed-conduit and broken-back transition, level invert, inlet pipe on 2 to 1 slope 31

31. Closed-conduit round-to-rectangular and square-to-rectangular transitions 32

CONTENTS vii

Number Page

32. Flow conditions, 12- by 24-inch closed-conduit transition, 4 f.p.s. velocity in pipeline, inlet pipe horizontal. 33

33. Scour patterns, outlet flows, 12- by 28-inch, closed-conduit transition, inlet pipe horizontal 34

34. Scour patterns, outlet flows, 12- by 24-inch, closed-conduit transition, 4 f.p.s. velocity in pipeline, inlet pipe horizontal 35

35. Flow conditions and scour patterns, outlet flows, 12- by 24-inch transition, 6 f.p.s. velocity, inlet pipe horizontal 36

36. Loss factors, 12-inch square to 12- by 24-inch rectangular transition, inlet pipe horizontal 36

37. Design sheet for small canal transitions 38

Introduction

THE BUREAU OF RECLAMATION water resource development projects embracing irrigation dis-tribution systems and related structures require large numbers of reinforced concrete transitions for pipelines which discharge into canals, as well as transitions for canals that discharge into pipe-lines. When the transitions are small—for ex-ample, for 36-inch or smaller pipes--the special forming of concrete required for warped transi-tions is usually not justified. For these small transitions, the broken-back type of transition made entirely of plane surfaces is used, as illus-trated in Figure 1.

In early designs of Bureau of Reclamation canal systems incorporating broken-back transitions as outlets from pipelines to canals, a loss value of

0.3 P

V --Ve2) was used. In this expression, V 2g 2g

is flow velocity in the pipeline, V, is velocity in the canal, and Os the acceleration due to gravity (approximately 32 feet per second per second). This 0.3 loss factor was derived intuitively and is apparently not supported by experimental data.

, A similarly derived loss of 0.1 (r _M

was 2g 2g)

FIGURE 1.—Typical field installation of a broken-back transition. Siphon outlet at station 521, West Lateral Rogue River Basin Project, Oreg. November 1961.

used when the transitions served as inlets fro canals to pipelines.

In recent years, there has been concern abou the possibility of actual losses being greater tha

1 714-653 0-64 2

ENGINEERING MONOGRAPH NO. 33

12 he 0.3 and 0.1 values used in the early designs. If the losses were appreciably greater, the struc-tures could be restrictions in the distribution systems and reduce the carrying capacity to less than the design values. This would have serious effect upon operation of the irrigation system when the lands were fully developed. Bureau engineers therefore believed it important to con-duct tests to determine the actual losses and to make any necessary changes in the design values. The investigations would be extended, as neces-sary, to obtain designs with lower losses.

A second important factor was the amount of scour or erosion in the canal immediately down-stream from transitions when they were used as outlets. The effect of changes in the upward slope of the transition invert, in the entering

pipeline, or in the rate of divergence of the transi-tion sidewalls on canal erosion were not known. Evaluation of these variables was necessary before design decisions could be made as to optimum outlet shape and canal bank protection requirements.

The many different operating conditions and design modifications involved in the testing pro-gram dictated that the studies be conducted in a laboratory where such changes could be made easily and quickly. To fill this need, studies were inaugurated and are continuing on an inter-mittent basis in the Hydraulics Branch of the Bureau's engineering laboratories in Denver, Colo. This monograph discusses. results that have been obtained thus far, and the equipment and pro-cedures used in the tests.

Test Equipment

MOST OF THE STUDIES were made using a canal section contained within a wooden structure supported about 5 feet above the laboratory

floor, and equipped with suitable piping and in-strumentation (Figs. 2 and 3A). The canal bed was formed of loose plastering sand that eroded easily and showed scour effects within a short time. Canal invert widths of 12 and 18 inches were used, and the canal sides lay on 1% to 1 slopes. The canal invert was level in the direction of flow. A template that rode on the top rails of the box was used as a guide for reshaping the canal bed be-tween runs (Fig. 3A).

In early studies, the transitions were tested only as outlet structures with the flow passing from the pipeline, through the transition, and into the canal. The 12-inch-diameter pipe that supplied water to the transition was placed level in part of the tests, and on a 2 to 1 upslope to the transition for other tests. The depth of flow in the canal was regu-lated by an adjustable tailgate at the downstream end of the model.

In later studies, the transitions were studied both as inlets • and outlets. The piping was modified so that, in addition to the flow described

above, water could be introduced into the canal from the tailgate end of the box to produce inlet flows into the transition and pipeline (Fig. 2).

Water leaving the test section was controllqd by the tailgate when outlet flow tests were mad*, and by appropriate valves in the piping systeln when inlet tests were made. The desired canal water surface elevations could therefore be main-tained.

The broken-back transitions, Figure 4, were constructed of %-inch plywood and were treatid to avoid excessive water absorption. In some cases, warped sections made of concrete were constructed within the confines of broken-bac* transitions (Fig. 5). The closed-conduit trap-sitions Were usually made of 16-gage sheet st el with external reinforcement, as required, and with %-inch-thick steel flanges upstream and dow stream.

The rate of water flow supplied to the model 4,s measured by calibrated permanently installOd Venturi meters in the laboratory's central water supply system. Water was taken from the labolla-tory's reservoir, pumped through the meters Old

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INLET TRANSITION OUTLET TRANSITION

CLOSE C, D A, B

OPEN A, B C, D

TABLE OF VALVE POSITIONS FOR

INLET AND OUTLET FLOWS

FIGURE 2.—Schematic views of test facilities.

HYDRAULIC DESIGN OF TRANSITIONS FOR SMALL CANALS 5

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A. Canal model with template in place for shaping sand bed. Closed conduit transi-tion installed with horizontal approach pipe.

C. Point gage for determining water surface elevation in canal.

B. Stilling wells and point gages for deter-mining hydraulic grade in 12-inch pipeline.

FIGURE 3.—Hydraulic model and instrumentation.

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HYDRAULIC DESIGN OF TRANSITIONS FOR SMALL CANALS

A. The surface is turbulent with Q=3.1 c.f.s., Vp=4.0 f.p.s., depth-----1.3 D. A boil occurs near the headwall.

B. Scour after 1 hour operation. Q=2.4 c.f.s., V= 3.0 f.p.s., depth=1.3 D. Sand was deposited in the transition.

FIGURE 5.—Flow conditions and scour. Outlet flow, broken-back transition modified with warped surfaces. 1 to 8 slope, 6-inch rise. Inlet pipe on 2 to 1 slope.

the model, and returned to the reservoir for re-circulation.

When a transition was used as an outlet, the pressure head in the 12-inch-diameter pipeline was measured at a station 1 foot (one-conduit diameter) upstream from the transition. When the transition was used as an inlet, the pipeline head was measured at a station 15 feet (15 D) downstream from the junction of the transition with the pipeline. Two piezometers, one on each side of the pipe on the horizontal centerline, were used to obtain the pressures. The pressure leads were connected to 1s-inch-diameter stilling wells, and point gage measurements were made of the free water surfaces within the wells (Fig. 3B). The water surface elevations in the canal were measured with point gages 15 feet downstream from the junction of the transition with the canal for outlet flows, and 4 feet upsteam from this junction for inlet flows (Fig. 3C).

Throughout the test program difficulty wa experienced in obtaining consistent data becaus the quantities being determined were small corn pared to the possible errors. Establishing wate surface elevations was of primary importance and several procedures were used to relate accurately the reading of one gage to another. Best result were obtained by filling the model to a 12-inch canal depth with no normal flow occurring, and after allowing considerable time for turbulence and oscillations to cease, obtaining the gage relationships.

During test runs, data were taken as soon as proper conditions were established and before extensive canal erosion occurred. Accurately determining the canal water surface was compli' cated by the fact that submerged instrument could not be used because it was necessary to mov the canal template up and down the model t reshape the bed. A water surface point gage wa used instead, and repeated readings were mad during a test run to obtain a good average figur for the undulating, wavy, or choppy water sur faces. Small stilling wells worked satisfactoril for the piezometer readings for the pipeline.

Operator technique had considerable influence on the observed data and with training and experience the accuracy and consistency improved greatly. Despite the efforts and precautions taken, the basic problem remained of seeking small values among relatively large potential errors. Therefore, the data presented herei may be accepted as representative, but mino variations and scatter can be expected.

In the closed-conduit outlet transition test velocity measurements were made of the flow the pipeline 1.3 D upstream from the transitio inlet and at the transition exit (Figs. 6, 7, and 8)I. For inlet flows, velocity traverses were made in the pipeline 1.1 D downstream from the junction of the transition with the pipeline. A 3/16-inch-diameter total head tube was used for measure-ments in the pipeline, and a rinch-diameter Prandtl-type pitot-static tube was used for measurements at the canal end of the transition.

Studies of closed-conduit expanding-outlet transitions were also made with a test facili, using air as the flowing fluid (Fig. 9). Air was drawn from the atmosphere through a 12-inch-diameter pipe into the centrifugal blower. It then passed through a 10.14-inch-diameter pipeline

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INLET FLOWS E. LOSSES vs FROUDE NUMBER

OUTLET FLOWS

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(-PIPELINE TRAVERSE STATION ,--OUTLET TRAVERSE STATION ,-CANAL

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8 ENGINEERING MONOGRAPH NO. 33

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Left Side 1.0

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A. PIPELINE UPSTREAM

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F. PIPELINE DOWNSTREAM

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V2= Velocity in canal,fps.

D = Pipeline diameter, feet

AHe = Energy loss from pipeline to

canal (outlet flows) or canal to pipeline (inlet flows) feet,

water.

10" canal depth

12 canal depth - 15 canal depth

FIGURE 6.-Velocity distributions and loss factors, 12- by 28-inch closed-conduit transition, horizontal pipeline.

B. OUTLET TRAVERSES ABOVE INVERT

Left Side

08 04 05 06 07

FROUDE NUMBER N, =

E. LOSSES-vs-FROUDE NUMBER OUTLET FLOWS

,-PIPELINE TRAVERSE STATION

FLOW

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V, = Velocity in pipeline,tu. V2 = Velocity in canal,fp.s. D - Pipeline diameter, feet

AHe = Energy loss from pipeline to canal (outlet flows) or canal to pipeline (inlet flows) feet, water.

0 „Its,

*FIGURE 8.-Velocity distributions and loss factors, 12- by 24-inch closed-conduit transition with divider pier, horizontal pipeline.

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G. LOSSES vs FROUDE NUMBER

INLET FLOWS

0.8

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OUTLET TRAVERSES 312/4 ABOVE INVERT

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F. PIPELINE DOWNSTREAM

FROM INLET TRANSITION

6

V, =Velocity in pipeline,f.p.s. V2 = Velocity in canal,tp,,s,. D = Pipeline diameter,feet

AHe = Energy loss from pipeline to canal (outlet flows) or canal to pipeline (inlet flows) feet, water.

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FIGURE 9.—Air model facilities for testing closed-conduit transitions. Air was drawn from the atmosphere, through the measuring orifice, and then through the outlet transition.

into the expanding transition being tested, and back into the atmosphere. The 10.14-inch-diameter pipeline was 63 inches long (6.2 D) for most of the tests, and was lengthened to 207 inches (20.4 D) for the remaining tests. A piezometer located 44 inches from the outlet was used with the 6.2 D-long pipe, and two diametrically opposed wall taps located 1 diameter from the outlet were used with the 20.4 D-long pipe.

Five expanding transitions made of light-gage sheet metal were tested (Figs. 9 and 10). All had inlets 10.14 inches in diameter, and all were 10.14 inches high at the outlet. The sidewalls expanded

at the rates of 00, 2%°, 50, 7%°, and 10 0 relative to the centerline, and the lengths were 20.28 inches, or 2 D. Piezometers were placed along the centerline of the right sidewall and along the invert, and also along the diverging transition element from the 450 point above the invert of the circular inlet to the lower righthand corner at the rectangular outlet (Fig. 11F). The piezometers were at stations 2, 5, 10, and 15 inches from the transition inlet.

Vertical and horizontal centerline traverses were obtained near the transition inlets and at the outlets with a 3i-inch-diameter Prandtl-type pitot-static tube. Pressures were measured with water-filled U-tubes, and the readings were recorded in tenths and hundredths of an inch. Readings were taken after sufficient time had elapsed for condi-tions to stabilize after starting the flow. The pitot-static tube was set at the desired position, the pressures read, and the tube moved to the next position. This process was repeated until the full effective length of the relatively short tube was within the conduit. The tube was then re-moved and inserted in the diametrically opposite station so the full length of each traverse could be covered. In addition to readings obtained with the pitot-static tube, readings were taken of the head differential across the 9-inch-diameter inlet orifice on the 12-inch inlet line to the blower, and at the wall taps in the 10.14-inch supply pipe. The barometric pressure and temperature were also measured so atmospheric densities could be computed.

22 Gage Sheet Metal

Gage Outlet Flange 2" wide 10.14 I.D. Pipe 6.2 and

20.4 diameters long__

—›— FREE DISCHARGE TO ATMOSPHERE

FROM CENTRIFUGAL BLOWER

DIVERGENCE A NO DIVERGENCE A 2/1 . 2 7

(On Each Side) 2/1 1.50

(On Each Side)

12 ENGINEERING MONOGRAPH NO. 3:3

12 Gage Inlet Flange to match 10"pipe

ELEVATION

TYPICAL ARRANGEMENT

20.28

FLOW

7

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FIGURE 10.—Closed—conduit transitions tested on air model.

PI PELINE

--0-

PIPELINE ,.. ‘ \ \

OUTLET

\

\ ‘

TRANSITION .4

''''....,

_ -04 0 04 08 I.E

DISTANCE FROM INLET INLET DIAMETER

C. 10.14 x 13.69" OUTLET (5° )

--0- .

PIPELINE

OUT

\ \

TRANSITION K

‘ ,

N.,

-04 0 04 08 1 DISTANCE FROM INLET

INLET DIAMETER

D. 10.14 x 15.4 8" OUTLET (7 1/20

)

0 E.0

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HYDRAULIC DESIGN OF TRANSITIONS FOR SMALL CANALS 1 3

-0.6

-0.5 PIPELINE

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TRANSITION

OUTLET

20

OUTL ET

-04 0 04 08 12

16


A. 10.14 x 10.14" OUTLET (00 )

T1ON

-04 0 04 08 12 II 20


B. 11.14" x 11.91" OUTLET (2 1/20 )

TRANS'

-0.6

-0- - 0.5

PIPELINE

OUTLET

TRANSITION

EXPLANATION Of sidewall

- 450 Element

- E Of bottom Divergence angle measured

relative to conduit centerline

12 Piezometers in each

transition

PIEZOMETER STATIONS:

10! 0.1973 D 14

0.493 D 10!14

= 0.986 D 10.14 15

- I 480 D 10.14

AT

PIE

ZO

ME

TE

R

2, -0.4

-0.3

-0.2

- 0.1

-04 0 04 0.8 12

16 DISTANCE FROM INLET

INLET DIAMETER

E. 10.14" x 17.30" OUTLET (100 )

20 SECTION AA

F. TYPICAL P1EZOMETER LOCATiONS

FIGURE 11.-Wall pressures on closed-conduit transitions 'used as outlets. Approach pipe 6.2 D long. Air model tests.

Investigation

Open-Channel Transitions

A number of open broken-back transitions were tested to determine the effect of upward slope of the invert, rate of sidewall divergence, degree of submergence over the outlet pipe crown, and slope of the incoming pipeline on energy losses and scour in the canal channel (Figs. 4, 5, and 12 through 19). In addition, the effect of placing humps on the transition invert to aid in spreading the flow, and the effects of other modifications such as changing the sidewalls to modified warped walls were tested. For convenience, these designs, operating conditions, and test results are briefly summarized in Figure 20. Loss factors for all the broken-backed transitions, including the ones modified with warped surfaces, were about 0.5 to 0.7 Mt, for outlet flows. The term Ah, equals the velocity head in the pipeline 1 diameter upstream from the transition, minus the velocity head in the canal 15 feet downstream from the transition.

The flow patterns through all the open transi-tions were generally similar. If the inlet pipe entered the transition horizontally, the stream

issuing from it tended to move straight through the transition into the canal, and large eddies moved upstream well up into the transition along either side of the jet (Fig. 12A). Scour o the canal bottom and on the side slopes wa appreciable in the loose sand and a sandbar wa built up across the canal 6 to 12 feet downstrea from the canal entrance (Fig. 12B).

If the inlet pipeline was sloped, the strea issuing from it rose in the transition to the wate surface to cause higher surface velocities and wave that scoured the canal slopes (Fig. 5A). Flo was nearly stagnant at the bottom of the transitio and, in some cases, sand was deposited in th transition. A wide sandbar built up several fee downstream from the canal entrance (Fig. 5B).

Changes in the slope of the transition inver from a minimum of 1 to 13.1 to a maximum o 1 to 5.5 had no apparent effect on the losses en countered or on the scour produced (Figs. 5, 1 through 19, and 20). Likewise, changes in diver gence angles of the outer walls of the transitions from the minimum of 16 0 per side to a maximum of 30 0 per side had no appreciable effect, although

15

1111,

A. Flow is confined mainly to passage center. Eddies occur at sides. Q--=3.0 c.f.s., Vp=3.8 f.p.s., canal depth=1.5 D.

16


B. Scour after 45 minutes operation. Q=3.0

C. Scour after 75 minutes operation with hump. c.f.s., Vp=3.8 f.p.s., depth=1.5 D. Q=2.4 c.f.s., Vp=3.0 f.p.s., depth=1.5 D.

FIGURE 12.—Flow conditions and scour patterns, outlet flows, broken-back transition, 1 to 8 slope, 6-inch rise, inlet pipe horizontal.

A. The water surface is mildly turbulent. Q=4.7 c.f.s., V=6.0 f.p.s., depth=1.3 D.


B. Scour after 1 hour operation. Q-4,7 c.f.s., V,= 6.0 f.p.s., depth =--1.3 D.

C. Scour after 45 minutes operation with hood installed in transition. Q=4.7 c.f.s., V,— 6.0 f.p.s., depth=1.3 D.

FIGURE 13.—Flow conditions and scour patterns, outlet flows, broken-back transition, I to 8 slope, 12-inch rise, inlet pipe horizontal.

A. The water surface is somewhat rough. Q=4.7 c.f.s., V,=6.0 f.p.s., depth=1.3 D.

A. Mildly turbulent water surface. Q=2.4 c.f.s., V,=- 3.0 f.p.s., depth= 0.8 D.


B. Scour after 1 hour operation. Q=4.7 c.f.s., V= 6.O f.p.s., depth=1.3 D.

B. Scour after 25 minutes operation each, with flow velocities in pipeline of 2, 2.5, and 3 f.p.s., depth= O.8 D.

Fi GURE 14.—Flow conditions and scour pattern, outlet FIGURE 15.—Flow conditions and scour pattern, outlet flows, broken-back transition, I to 8 slope, 12-inch rise flows, 80° broken-back transition, 4-inch rise, inlet pipe inlet pipe on 2 to 1 slope. horizontal.


let pe

FIGURE 17.—Flow conditions and scour pattern, ou flows, 25° broken-back transition 4-inch rise, inlet p on 2 to I slope.

A. Mildly turbulent water surface. Q=2.4 c.f.s., Vp=3.0 f.p.s., depth=0.8 D.

B. Scour after 30 minutes operation each at flow velocities in pipeline of 2, 2.5, and 3 f.p.s., depth=0.8 D.

FIGURE 16.—Flow conditions and scour pattern, outlet flows, 25° broken-back transition, 4-inch rise, inlet pipe horizontal.

A. Turbulent water surface. Q=2.4 c.f.s., Vp=3.0 f.p.s., depth=0.8 D.

B. Scour after 30 minutes operation each at flow velocities in pipeline of 2, 2.5, and 3 f.p.s., depth--0.8 D.

A. Scour after 23 hours, VD--2, 2.5, and 3 f.p.s., canal depths of 8, 10, and 12 inches. Pipeline horizontal.

B. Scour after 2% hours, VD-2, 2.5, and 3 f.p.s., canal depths of 8, 10, and 12 inches. Pipeline on 2 to 1 slope, depth--0.8 D.

CURE 18.—Scour patterns, outlet flows, 20° broken-back transition, 4-inch rise, 20-inch canal invert.

lilmited data show a slightly lower loss for a 25';

atagle. Even altering the outer walls by con- structing warped surfaces within the confines of

2C ENGINEERING MONOGRAPH NO. 33

the broken-back walls was not significantly effective.

Different submergences above the crown of the pipe at its juncture with the transition showed little effect in early tests. More detailed investi-gations with the 20°, 25°, and 30° broken-back transitions showed lowest losses with small sub-mergences, and progressively higher losses with submergences exceeding about 0.1 pipe diameter (Fig. 21A).

Several "humps" were placed on the transition invert a short distance downstream from the pipe exit to help spread the floe and obtain smoother conditions with more uniform velocities at the canal entrance (Figs. 4, 12C, 22B, and 22C). Improvements in flow conditions and reductions in scour occurred, but the losses were either unaffected or increased. The usefulness of humps appeared to be restricted to reducing scour in the canal.

A qualitative measurement of riprap needed to control scour in the canal was obtained by placing a 4-inch-thick layer of 13-inch gravel in the first 6 feet of the model canal. Tests were made with the 1 to 8 slope, 6-inch rise transition with warped walls, and a horizontal inlet pipeline (Fig. 19). A flow velocity of 3 feet per second in the pipeline failed to move any gravel or any appreciable amount of sand in the bed downstream. A velocity of 4 feet per second also failed to move the rock and moved only a very small amount of sand. At a pipeline velocity of 6 feet per second, the rock remained stable, but considerable erosion occurred in the sand farther downstream (Fig. 19C). It was apparent that this 13-inch rock was capable of protecting the model canal from scouring tendencies. By geometric scaling, this rock is equivalent to 0.125 times the pipe diameter. No tests were made with rocks of other sizes.

Noticeable reductions in head loss, improve-ments in flow distribution, and reduction in scour were achieved when closed-conduit expanding sections were used in conjunction with the open transitions. A short submerged shelf projecting downstream from the transition headwall just above the pipeline crown in a 1 to 8 sloping transition (Fig. 20) cut the loss factor from about 0.6 to less than 0.5. A longer hood that created a 4 D-long closed conduit within a 1 to 8 transition (Fig. 13C) and had a maximum divergence rate of 8Y2° per side reduced the loss factor to 0.21. A

•

YD'A LIC DESIGN OF TRANSITIONS FOR SMALL A AL

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For

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FIG

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Table

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tran

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ons.

30 ° 1

TRANSITION

........ ....... ..r........e..... ...."......'n*.-

TRANS I11 20°

25° TRANSITION.-- , 7.' ••

.•

0.1 0.2 0.3

04

SUBMERGENCE FACTOR, C

A. BROKEN BACK TRANSITIONS - OUTLET FLOWS

0.7

LT- 0.6

0 0

0.5


23

12" X 24 WITH DIVIDING PIER -------,... ......2%.-• ..."

I

1

0

........ .....

."'""....

.••••••••"" ......

:- 2" X 28"

.....•

TRANSITION 0

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24"

........:

TRANSITION

-0.1 0 0.1

0.2

03

SUBMERGENCE FACTOR, C

B. 6D-LONG, CLOSED CONDUIT TRANSITIONS - OUTLET FLOWS

K . 1

_ SUBMERGENCE 1

lie PIPE DIAMETER

12"X 24 WITH DIVIDING PIER -

--

----Ie X 28" TRANSITION

• .....

"----12" X 24 TRANSITION

--.-........,

-01 0

0.1

02

00

SUBMERGENCE FA GTOR ,

C. 6D-LONG, CLOSED CONDUIT TRANSITIONS - INLET FLOWS

FIGURE 21.—Effect of submergence on loss coefficients—N1= 0.71, Vz,=4.0 f.p.s.

short closed-conduit transition from the 12-inch circular pipe to a 12-inch square section, inserted in the pipeline just ahead of the rectangular 1 to 8 broken-back transition, reduced the 0.6 loss factor to less than 0.4. It was apparent that the best opportunities for improving transition per-formance lay in closed-conduit, gradually expand-ing sections.

Closed-Conduit Transitions—Air Model Tests

To determine the performance of a series of ex-panding closed-conduit transitions, air model tests were made (Figs. 9 and 10). The shapes of the transitions were selected after considering design problems involved in coupling them with open-type, but shortened, transitions. To avoid ex-cavations deeper than for present structures, no downward divergence relative to the centerline was used. Similarly, to avoid lowering the struc-ture to maintain submergence over the crown of the conduit, no upward divergence relative to the

centerline was used. Thus, the height of the transition at the outlet was the same as at the inlet and equal to the diameter of the pipelin All divergence in the closed-conduit transitior4s occurred through divergence of the sidewalls an through the change in section from circular inle s to square or rectangular outlets.

Each transition was first tested on the 6.2-diameter-long approach pipe, and velocity tra erses were taken horizontally and vertically at t e inlet and outlet (Fig. 23). There was a sligl4t distortion in the inlet velocity profile with t e round-to-square transition, and the distortio became progressively greater as transition e pansion increased. The outlet profiles showeF1 that the flow expanded well and followed the diverging walls in the 00, 2%°, and 5° transitio s and also followed the walls, but to a lesser exte t in the 734° transition. The 10° diverging section was too abrupt, and flow broke away from t e right side and the upper and lower right come so that reverse flow occurred.

The somewhat distorted velocity distribution 4t the transition inlets apparently had appreciable effect upon the ability of the flow to follow t e expanding boundaries. A 12-foot extension w added to the approach pipe to produce a section 20.4 diameters long and obtain a more fully d veloped and uniform distribution. Tests will the 00 divergence transition showed nearly sy metrical velocity distributions at both the inlet and outlet (Fig. 24A). However, tests with the 100 transition showed ,noticeable velocity dip-tortion in the horizontal traverse at the inlet, apparently due to the severe separation along the right side of the outlet. This separation $s greater than the separation that occurred with the short approach pipe. It was concluded that rp-gardless of the uniformity of approach conditions, the 100 transition was too abrupt to control the discharging flow.

Pressures were subatmospheric at the approach pipe wall taps just upstream from the transitions. This was expected and is due to recovery of head, wherein the velocity head of the entering stream s converted into pressure head as the flow expan s and slows. The pressure level into which t transitions discharge is atmospheric, and hence t e pressures in the approach conduit and upstreatn

) parts of the transitions where the flow is fast will be less than atmospheric. The extent of the su -

0.2

E 0 u-,

0.5

Ui

E 0.4 Ui

0.3

2, •

‘44:iX1":"t -

4 ii: I': •


•

A. A hump occurs in the water surface above the Design 2, hump-like de-flector on the floor. Q=4.7 c.f.s., V=6.0 f.p.s., canal depth=1.3 D.

C. Scour after 1 hour operation 33/8-inch-high deflector. Q=4.7 c.f.s., V1,=6.0 f.p.s.

operation 64-inch-high V=6.() f.p.s.

B. Scour after 1 hour deflector. Q=4.7 c.f.s.,

IGURE 22.—Flow conditions and scour patterns, outlet flows, combination closed-conduit and broken-back transition with floor deflector, 1 to 5.5 slope, 12-inch rise, inlet pipe horizontal.

14 08 1.0 1.2 YVAVG.(EXIT)

0.8

0.6

0.4

0.2

L/L

1.0 LEFT TOP 1.0

0.8

06 t /L

04

02

0.8

0.6 L/L

0.4

0.2

0 0 RIGHT TOM 1 08 0.9 10

YVAVG. (ENTRANCE) A. 10.14" x 10.14" OUTLET (0°)

10

V/VAVG. (ENTRANCE) B. 10.14" x 11.91" OUTLET (21/2° )

VL

/ (EXIT) 0 08 10 I 2 I 4 08 0.9 1.0 11

VA,'AVG

0 0 08 10 12 14 08 09 10 V/VAVG. (EXIT) V/VAVG. (ENTRANCE)

a

06 a

1.0

0.8

HI 04

0.2

1 1.0 (2

V/VAVG. (EXIT) 0 08

10

0.8

0.6

0.4

0.2

1.0

0 08 09 10 11 VVAVG (ENTRANCE)

1

1.0

0.8

0.6

0.4

0.2

1.0

0.8

0.6 L/L

0.4

0.2

0

0.8

0.6

0.4

0.2

L

1.0

0.8

0.6

0.8

0.6

0.4

0.2

0.9 I 0 II V/ t, (ENTRANCE)

0 08 10 I 2 14 V/VAVG. (EXIT)

16

1.0


C. 10.14" x 13.69 OUTLET (5° ) D. 10.14 x 15.48" OUTLET (7 1/2° )

EXPLANATION

--.---Horizontal traverse -.-Vertical traverse Inlets of all transitions 10.14 Diameter Divergence angle is measured relative

to the conduit centerline.

E. 10.14 x 17.30" OUTLET ((0° )

FIGURE 23.-Velocity distribution for closed-conduit transitions used as outlets, approach pipe 6.2 D long. Air model test

TOP

BOTTOM

0.9 1.0 \//v " AVG.

ENTRANCE

1.2 1.0 0.8 2.0 1.6 1.8

TOP

BOTTOM

1.4 \qv " AVG.

EXIT

LEFT • • TOP •

•

•

• • •

• •

y • • •

V t • ;

• • •

.

•

•

• •

•

• .

•

RIGHT •

•

• • • • BOTTOM

0.8

0.6

0.4

0.2

1.0

0

LEFT TOP

B OTT 0 M


A. 10.14" x 10.14" OUTLET (00 )

0.8 0.9 1.0 V/ / VAVG.

ENTRANCE

0.8 1.0 1.2 1.4

Y/VAvG.

EXIT

1.6 1.8 2.0

B. 10.14" x 17.30" OUTLET (100 )

Inlets of both transitions 10.14" diameter o — Horizontal traverse O — Vertical traverse

FIGURE 24.— Velocity distribution for closed-conduit transitions used as outlets, approach pipe 20.4 D long. Air model tests.

FIGURE 25.-Draft head at inlet and loss coefficients for closed-conduit transitions used as outlets. Air model tests.

The greatest head recovery occurred in a transition with a divergence of 70 to 8° and was 55 percent of the inlet velocity head.

The loss in total head from the transition inlet to the atmosphere, divided by inlet velocity head, was similarly plotted against sidewall divergence (Fig. 25B). This loss factor, K, was lowest for a divergence of 7.5° to 8° and was 44 percent of the inlet velocity head. The pressures on the transi-tion walls were negative with respect to the outlet head (atmospheric) in all cases except near the

o -62 DIAMETER -LONG APPROACH PIPE

A -20.2 DIAMETER- LONG APPROACH PIPE

4 6 10 SIDEWAL DIVERGENCE RELATIVE TO (DEGREES)!3

A. DRAFTHEAD AT INLETS VS. RATE OF EXPANSION

0 -6 2 DIAMETER -LONG .APPROACH PIPE A-202 DIAMETER-LONG APPROACH PIPE

i I I I I I

,.. HEAD DROP FROM TOTAL INLET HEAD TO ATHOS VELOCITY HEAD AT INLET

0.7

0.8

2 4 6 8 SIDEWALL DIVERGENCE RELATIVE TO Q (DEGREES)

B. LOSSES VS. RATE OF EXPANSION

Transitions discharge directly into atmosphere

Transition outlets 10.14 Inches high

04 0 10

LT. 0.6

0.5

-0.6

1- -0.5 Ui

-0.4

Ui

-0.2

0 >j -0.1

FLOW

o°

FLOW 10.1

TRANSITION HEIGHT.10.14" IN ALL GASES - INLET DIAMETER-10.14"

PLAN VIEWS

.4 0.8

0.

2 4 6 12 14 16 18 20 22 DISTANCE LONG TRANSITION Q (INCHES)

A. CIRCULAR-TO-RECTANGULAR T ANSITIONS WITH CONSTANT HEIGHT

0.4o

ui 1.4 Ui u.

'et' 1.2

UI 1.0


atmospheric pressure level is a direct measure of the amount of head recovery, or effectiveness of the expanding transition. The pressure head at the inlet divided by the inlet velocity head, produced dimensionless parameters which were plotted against degrees of sidewall divergence (Fig. 25A).

outlet of the 0.0 transition (Fig. 11). The pressures at a given station became generally more negative as the rate of transition divergence increased, until the 10° transition was approached and the trend reversed. Flow separation occurred in this transij tion, and the effectiveness and efficiency dropped below that of the 732° transition. In all cases, the lowest pressures were obtained on the transition element leading from a 45° point on the circula inlet to an outlet corner. These elements diverg more rapidly than any others in the transitions.

For comparative purposes, plots of cross-sec tional areas versus distance along the transition are presented for the transitions tested and for coni transitions (Fig. 26).

_

--AREA I I

OF 10.14"

• ,

DIAMETER INLET.0.561 DIVERGENCE ANGLE MEASURED

FROM TRANSITION i I I I I

4 6 8 10 12 14 16 18 DISTANCE ALONG TRANSITION (INCHES)

B. CONIC TRANSITIONS

FIGURE 26.-Area curves for constant height, circular-t rectangular transitions and for conic transitions.

Loss coefficients, K, for conic expanding transi tions of 21/2 ° and 7%2° relative to the centerline and discharging directly into the atmosphere, were found in previous tests to be 0.273 and 0.499

1.8

1.6

06

0.4 20

22


Standard 12 F la ng

A 12" Pipe-,

2 Piezometer

PLAN

24"

2 Piezometer

Standard 12" Flange.,,

A 12" Pipe.

t 4

2 Piezometer Taps/ —9 4-,

Humps used in ,' part of tests'

PLAN

U--:

mlo ',.._

k 24"

2 Piezometer Taps,

68,1," 66"

SECTION C-C

)0( SECT ION A -A SECTION B-B

A . 7 1° CLOSED AND 1 , 5.5 SLOPED, 12 INCH RISE OPEN TRANSITION

-

LARGE HUMP

SECTION A-A SMALL HUMP

B. 7Ie CLOSED AND HORIZONTAL OPEN TRANSITION 2 C. HUMPS

FIGURE 27.—Combination transition using closed-conduit and open-channel broken-back section, with and without humps.


29

respectively, based on the inlet velocity heads.' These values show a trend of greater loss with greater divergence to 7X°, instead of the decreasing loss shown by the round-to-rectangular transitions. This difference is explained by a comparison of the area curves (Fig. 26) that show that conic sections enlarge much more rapidly than the round-to-rectangular transitions of the present study, and indicates that considerable separation, and hence loss, occurred in the 7X° cone. This separation was found to exist in the turnout structure conic transition.

Combination Closed-Conduit and Open-

Channel Transitions

The relatively high efficiency of the closed-conduit expanding transitions was partially ex-ploited by placing 2 D-long, round-to-rectangular transitions between the end of the circular pipeline and a shortened and modified broken-back tran-sition (Fig. 27). The height of the closed tran-sition was kept the same as the diameter of the pipe and the sides diverged 7X° relative to the centerline. The length was 2 D and the outlet measured 12 inches high by 18% inches wide, with an area 2.8 times greater than at the inlet. A 5.5 D-long, upwardly-sloping, open-channel tran-sition adapted the rectangular section to the trapezoidal section of the canal.

The loss coefficient for outlet flows was about 0.4 with the inlet pipe horizontal, and about 0.2 with it rising on a 2 to 1 slope (Fig. 20). With the pipe horizontal, waves were smaller and less powerful than in previous transitions, but scour remained appreciable (Fig. 28). This was appar-ently due to flow from the closed pipeline contin-uing straight through the open transition along the floor without appreciable spreading or slowing. Large back eddies were present at the sides in the open transition. Several humps were placed on the floor to "lift" this flow stream and help spread it. Scour was decreased when a 6%-inch-high wedge-shaped hump was used, but remained almost unchanged with a 3%-inch one (Figs. 22 and 27). Better flow conditions occurred when the inlet pipe was placed on a 2 to 1 upslope (Fig. 29). Wave action persisted, but flow was

1 Bureau of Reclamation, "Hydraulic Model Studies of the San Jacinto-San Vicente Turnout and Metering Structure, San Diego Aqueduct Project, California," Hydraulic Laboratory Report No. Hyd-365, January 26, 1953.

A. Water surface is mildly turbulent in transition, but smooth in canal. Q=4.7 c.f.s., Vp= 6.0 f.p.s., canal depth=1.3 D.

B. Scour after 1 hour operation. Q=4.7 c.f.s., V0=6.0 f.p.s., canal depth=1.3 D.

FIGURE 28.—Flow conditions and scour pattern, outlet flows, combination closed-conduit and broken-back transi-tion, 1 to 5.5 slope, 12-inch rise, inlet pipe horizontal.

distributed more uniformly across the section upon reaching the canal. Considerable flow was present along the broken-back transition invert, although the greater part of the flow was near the surface. The scour was moderate and the energy loss coefficient decreased to 0.21.

Additional tests were made with an open tran-sition having a horizontal invert (Figs. 27B and 30). The submergence over the crown of the


water surface was somewhat choppy, and waves that were carried into the canal produced moderate bank erosion. The flow moving downstream extended completely across the water prism at the canal entrance, and from the water surface down-ward to 4 or 5 inches above the canal invert. The lowest layers of water were not in significant motion and bottom scour was not apparent. The loss coefficient decreased to 0.15, possibly due to the greatly decreased submergence at the outlet of the closed conduit.

A. Scour after 1 hour. Q=3.1 c.f.s., V= 4.O f.p.s., canal depth=1.3 D.

B. Scour after 1 hour. Q=4.7 c.f.s., V=6.0 f.p.s., canal depth=1.3 D.

FIGURE 29.—Scour patterns, outlet flows, combination closed-conduit and broken-back transition, 1 to 5.5 slope, 12-inch rise, inlet pipe on 2 to 1 slope.

closed-conduit outlet for a 15-inch (1,3 D) flow depth in the canal 'was 0.3 D, as compared. with 1.3 D for the sloped, open transition, The tests were made with a 2 to 1 sloping pipeline. The

Closed-Conduit Transitions—Hydraulic Tests

The losses of the combined closed-conduit and open-channel transitions were significantly lower than for the usual open ones, and scouring was reduced. Consequently, longer round-to-rectan-gular closed-conduit transitions that terminated in a headwall normal to the canal (Fig. 31) were studied. The water discharged directly through the headwall into the canal section for outlet flow tests, and through the headwall into the transition for inlet flow tests. No further transitioning was used. The closed-conduit transitions exploited the fact that more orderly and complete expansion, and hence slowing of the flow, can be obtained in closed conduits than can be obtained in the usual open-type transitions. Ideally, based on the areas of the inlet and outlet, a two-thirds velocity reduc-tion can be achieved, and about 90 percent of the velocity head can be recovered in a closed-conduit transition 6 diameters long and with a moderate rate of divergence.

12- by 28-inch Transition.—A closed-conduit transition having a 12-inch-diameter inlet, a 12-inch-high by 28-inch-wide rectangular outlet, and an overall length of 72 inches (6 D) was con-structed and tested (Figs. 2 and 31A). The transi-tion sloped upward 4 inches and the top of the exit was to be level with or slightly beneath the normal canal water surface. The transition termi-nated in a vertical headwall placed normal to the canal; the 12-inch-diameter inlet pipeline was placed horizontal.

, Relatively good flow conditions occurred near the headwall and in the canal. Conditions were similar to those shown in Figure 32. The least desirable conditions were present at a 15-inch flow depth (1.25 D), where significant return eddies occurred along the banks at the water surface near the headwall. These eddies eroded the canal bank


31

slopes noticeably (Figs. 33B and 33C). At a 12-inoh depth (1.0 D), these eddies were small enough to be of little consequence and erosion was minor (Fig. 33A). At a 10-inch depth (0.83 D), the eddies were not significant, but flow velocities along the canal banks and invert were higher than desired and erosion increased. The scours at the 0.83, 1.00, and 1.25 D depths compared favorably with those of the open and the combination open-closed transitions.

Loss coefficients for the 12- by 28-inch transi-tion, when it was used as an outlet, were quite low and equal to 0.11, 0.09, and 0.11 for canal depths of 0.83, 1.00, and 1.25 D, respectively (Figs. 6, 20, and 21). Loss coefficients when the transition was used for inlet service were 0.34, 0.37, and 0.40, respectively. It was apparent ' that 'very low energy losses were obtained for outlet service, and that no penalty was incurred in erosion in the canal or in losses for inlet service.

Detailed studies of the flow conditions were made by velocity traverses across the inlet pipe-line and the outlet portal (Fig. 6). The measure-ments showed undesirable flow separation along the left side and the corners of the transition when it was used in outlet service. This indicated excessive divergence of the flow passage and a design unnecessarily expensive due to greater than required width.

12- by 2.4-inch Transition.—A 6 D-long transi-tion with a 12-inch-diameter inlet and a lesser divergence rate to a rectangular outlet 12 inches high by 24 inches wide was constructed (Fig. 31B). When used as an outlet it produced flow in the canal generally similar to that obtained with the previous closed transition (Fig. 32). Scour in the canal was relatively small at all flow veloci-ties and water depths and comparable with the best of the other designs (Figs. 34 and 35). The loss coefficients decreased to 0.09, 0.07, and 0.11 for the 0.83, 1.00, and 1.25 D flow depths (Figs. 20 and 21). The reduced scour and lower losses attested to the excellent performance of the transition in expanding the flow, and velocity. measurements at the outlet confirmed the con-clusion (Fig. 7).

The transition performed satisfactorily when used as an inlet. Good flow distribution was present in the pipeline, and loss coefficients of 0.35 were determined for canal depths of 1.00 and 1.25 D (Figs. 7, 20, and 21). These losses

A. Somewhat turbulent water surfaces occur in the transition and canal. Q=4.7 c.f.s., 1Tp=6.0 f.p.s., canal depth=1.3 D.

B. Scour after 1 hour operation. Q=4.7 c.f.s., V= 6.O f.p.s., canal depth=1.3 D.

FIGURE 30.—Flow conditions and scour pattern, out t flows, combination closed-conduit and broken-back trans tion, level invert, inlet pipe on 2 to I slope.

compared very favorably with those of all oth designs.

Field installations might require transitions o large. that the flat tops near the head wall wou pose structural problems. This would be le :s complicated if the span were cut in half by us a center supporting wall or pier. To determi e the effects of such a pier on the flow and losses,

A, —I A

i2" L W Pipe

FLOW

PLAN

SECTION A -A -

c

12 L.W. Pipe -,,

Divider Wall-,

- 18" - -

PLAN

5.-H"

-41

SECTION B-B

k---28

SECTION C-C

SECTION D -D

-

SECTION E-E


A. 12-INCH ROUND TO - 12x 28-INCH RECTANGLE

SECTION A -A

B. 12-INCH ROUND TO 12 x24- INCH RECTANGLE

A

7

SECTION F -F PLAN

11"

12 L W. Pipe X

A G

SECTION A-A SECTION G-G

C. 12-INCH SQUARE TO 12x24-INCH RECTANGLE

FIGURE 31.—Closed-conduit round-to-rectangular and square-to-rectangular transitions.

-24"-


A. 0.83 D canal depth.

B. 1.00 D canal depth.

C. 1.25 D canal depth.

FIGURE 32.—Flow conditions, 12- by 24-inch closed-conduit transition, 4 f.p.s. velocity in pipeline, inlet pipe horizontal.

A. Scour after 2 hours operation. Q=3.1 c.f.s., V=4.0 f.p.s., canal depth=1.0 D.

34


B. Scour after 2 hours operation. V=4.0 f.p.s., canal depth=1.25 D.

C. Scour after 1 hour operation. V=6.0 f.p.s., canal depth=1.25 D.

FIGURE 33.—Scour patterns, outlet flows, 12- by 28-inch, closed-conduit transition, inlet pipe horizontal.


A. Scour after 1 hour operation. Canal depth= 0.83 D.

B. Scour after 1 hour operation. Canal depth=1.00 D.

C. Scour after 1 hour operation. Canal depth=1.25 D.

FIGURE 34.—Scour patterns, outlet flows, 12- by 24-inch, closed-conduit transition, 4 f.p.s. velocity in pipeline, inlet pipe horizontal.

tests were made with an 18-inch-long pier in the transition (Figs. 8, 20, 21, and 31). The pier was 0.2 D thick and had a rounded upstream end and a blunt face at the downstream end. Its presence increased the outlet loss coefficients to 0.10, 0.12, and 0.17, and the inlet loss coefficients to 0.39 and 0.40. A part of this increased loss is

undoubtedly due to the more distorted velocity distribution that occurred in the tests with the pier present (Fig. 8). When this increased dis-tortion was first noted the pier was suspected of being out of alinement. A check of the alinement

showed it to be satisfactory.

---- tr."-

36

ENGINEERING MONOGRAPH NO: 33

A. 1.00 D canal depth.

C. Erosion after 1 hour, 1.25 D depth.

FIGURE 35.—Flow conditions and scour patterns, outlet flows, 12- by 24-inch transition, 6 f.p.s. velocity, inlet pipe horizontal.

Square Inlet on .12- by 24-inch Transition.—Consideration of the cost of forms to make round-to-rectangular transitions led to questioning whether or not simpler square-to-rectangular

designs would perform satisfactorily. Therefore, a 6 D-long transition with a 12-inch-square inlet instead of a round one, and a 12- by 24-inch rec-tangular outlet was tested (Fig. 31C). The loss coefficients for outlet flows were 0.20,0.20, and 0.23 for depths of 0.83 D, 1.00 D, and 1.25 D. These values represent about a 100 percent increase over those obtained with the circular entrance design. For inlet-type flows, the loss coefficients were 0.50, 0.50, and 0.51 (Fig. 36). These values are about 25 percent higher than for the circular inlet transition.

In terms of actual head loss in a prototype structure at flow velocities of 8 feet per second, the outlet losses for the square-to-rectangular transi-tion are about 0.10 feet of water more than for the round-to-rectangular design. In many instances this small additional loss may be insignificant, and the lesser construction cost of the square-to-rectangular transition will dictate its use.

0.2

e>5._

0I 0.3 04 05 06 07 0.8

FROUDE NUMBER = V/i671

A. LOSSES — VS. FROUDE NUMBER

OUTLET FLOWS

0.40 3 0.4 05 06 07

FROUDE NUMBER = Viii—ii

B. LOSSES VS. FROUDE NUMBER INLET FLOWS

10 canal depth

0 12 canal depth

A 15 canal depth

V, = Velocity in pipeline, tIls•

V2 = Velocity in canal, f.p.s. H = Energy loss from pipeline to canal ( outlet flows)

or canal to pipeline (inlet flows), feet of water.

FIGURE 36.—Loss factors, 12-inch square to 12- by 24-inch rectangular transition, inlet pipe horizontal.

0.7

cr

0.6

0.5

OS

Conclusions

THE ENERGY LOSSES for conventional, broken-back, open-channel transitions discharging from pipes into small canals is 0.6 to 0.7 times

the difference in velocity heads in the pipe and in the canal (Fig. 20 and Fig. 37). This velocity

v2 v2 head difference' --'—' ' is termed Ahv. 2g 2g

Reasonable changes in angle of divergence of the sidewalls, of the slope of the invert of the open transitions, or of the attitude of the inlet pipeline, had little effect upon energy losses (Figs. 4 and 20).

Outlet losses were reduced to 0.4 Aht, and less when short, closed-conduit, expanding transitions were placed between the pipeline and modified, broken-back transitions (Fig. 27 and Fig. 37).

Outlet losses were reduced to 0.1 Ah, with 6 D-long closed-conduit transitions having circular inlets and rectangular outlets, and which dis-charged directly into the canal through a vertical headwall placed perpendicular to the canal axis (Fig. 3A and Fig. 37).

The addition of a dividing pier to decrease the structural span of the roof near the outlet of the round-to-rectangular transition increased the losses to about 0.13 M.

Changing the 6 D-long transition to provide a square instead of the more difficult to form circul r inlet increased the outlet losses to 0.20 ,A16,, a d the inlet losses to 0.50

Outlet losses of existing broken-back transitions can be materially reduced by installing properly designed hoods within the structures to form co trolled, closed-conduit expanding sections (Fi 13C and 20).

Losses for inlet flows were about 0.4 to 0.5 A for all transitions tested (Fig. 20).

Scour or erosion in the loose sand of the can 1 bed was extensive with conventional, broken-ba k transitions (Fig. 5 and Figs. 12 through 19).

Selected humps or flow spreaders on the inver s within open transitions significantly reduced sco r (Fig. 5 and Figs. 12 through 19). The hum s tested created a slight increase in head loss.

Scour was not appreciably affected by chang s in the side-wall divergence or invert slopes of t e open transitions.

Scour with the combination closed-conduit a d open-channel transitions was less than for t e conventional transitions (Fig. 22 and Figs. through 30).

37

1 . 0 D.-- -


Barrel of pipeline attached to transition:

Loss as an inlet = 0.50[h Loss as an ,outlett.= 0.656 hv Scour - moderate to extensive

A. CONVENTIONAL BROKEN - BACK TRANSITION

Pipeline barrel connects to transition with round - to- rectangular pipe transition:

Loss as an inlet = 0.40 nhv Loss as an outlet = 0.40Ahv Scour - moderate

B. MODIFIED BROKEN - BACK WITH ROUND - TO - RECTANGULAR TRANSITION BETWEEN STRUCTURE AND PIPELINE

D.->1

6 D - long pipe transition connects pipeline to headwall across canal:

Loss as an inlet = 0.40hv Loss as an outlet = 0.10h Scour - moderate

C. ROUND - TO - RECTANGULAR PIPELINE TRANSITION TERMINATING IN HEADWALL

D = Pipeline diameter

6h = 2 Vp/2 g VG2/2 g , where Vp and Vc are the CVA velocities in

the pipeline and canal, respectively. Loss/

inh

For outlets, loss is (hp + VF%g) hc

For inlets, loss is (hc + v1/2g - hp

loss to measuring station.

FIGURE 37.—Design sheet for small canal transitions.

V 2 + C g

VF/ g ) pipeline


Scour was reduced, in most cases, when the pipeline to the transition was on a 2 to 1 slope instead of horizontal.

Scour with the 6 D-long, closed-conduit transi-tions was about the same as with the combination transitions, and less than for the conventional transitions (Figs. 32, 33, 34, and 36).

In general, scour was nominal with flow veloci-ties of 4 feet per second in the 12-inch-diameter pipe, and severe with velocities of 6 feet per second. By scaling to larger structure sizes, ac-cording to Froude laws, these velocities are equivalent to 5.7 and 8.5 feet per second for 24-inch pipe, and 8 and 12 feet per second for 48-inch pipe.

A 4-inch-thick layer of 1X-inch gravel extending 4 feet downstream from the transition of the 12-inch test installation provided excellent scour pro-tection at the transition outlet (Fig. 19). Erosion

occurred beyond this blanket when the velociti were high, waves were appreciable, or both.

The optimum divergence of the sides of shor circular-to-rectangular, constant height, close conduit transitions is 7X° relative to the cente line (Figs. 10, 11, 23, 24, and 25). For long :r transitions the divergence should be decreased about 50 per side.

For both inlet and outlet flows submergenc s up to 0.25 D over the crown of the pipeline at i s junction with the headwall had only modera e effects upon head losses in the broken-back a the 6 D-long closed-conduit transitions (Fig. 21 Higher submergences tested in the broken-ba transitions further increased the losses. Negati e submergences down to —0.17 D, which is tant mount to not having the transition full at tie headwall, indicated only minor head loss increas s for outlet flows.

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U. S. GOVERNMENT PRINTING OFFICE: 1964 0 - 714-653