20320140503004

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),

ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 32-49 © IAEME

32

EXPERIMENTS TO STUDY THE EFFECT OF DISSIPATION BLOCKS

UPON ENERGY OF FLOW DOWNSTREAM THE COMPOUND WEIRS

Imad H. Obead Dept. of Civil Eng.,College of Eng., University of Babylon

Riyadh Hamad Dept. of Civil Eng.,College of Eng., University of Babylon

ABSTRACT

The objective of this study was to investigate the hydraulic characteristics such as energy

dissipation, reduction of hydraulic jump and roller length on unconventional types of blocks using

the experimental works. Values of the relative energy dissipation ratio (E2/E1), relative length of

hydraulic jump (Lj/Y2), and relative roller length (Lr/∆Y) for different blocks in this study were

found in terms of the primary Froude numbers. Results indicated that the compound weir with (60°,

90°) lower V-notch with all dissipation blocks have a high efficiency especially at the high

discharges. Also, the hydraulic characteristics values of applied discharges on the surface of the

triangular cut angles with (45°, 60

°) were better than other configuration of blocks.

Key words: Dissipation, Blocks, Energy, Compound, Weirs

1. INTRODUCTION

The specific energy of the flow always decreases during the flow. So the specific energy at

any discharge ratio of the flow either decreases or increases. The specific energy of the

discharge ratio is depends on the flow depth (Giglou et al,. 2013). In the small low-head hydraulic

structures, the Froude Number of discharge flow is typically not more than 4.5, which means it is a

low Froude Number flow. Bottom-flow energy dissipater is usually adapted to low-head hydraulic

structure, by means of engineering measures, the hydraulic jump is controlled to the stilling basin,

and energy is dissipated by the Surface vortex roll and a strong vortex turbulence of hydraulic jump.

To improve energy dissipation rate, decrease the length and height of stilling basin, the dissipation

blocks are applied on the apron to form a forced hydraulic jump. Usually, when the energy is

dissipated by hydraulic jump, a serious fluctuating pressure was generated on the stilling basin apron,

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ISSN 0976 – 6308 (Print)

ISSN 0976 – 6316(Online)

Volume 5, Issue 3, March (2014), pp. 32-49

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33

and the fluctuating uplift force will sometimes make the apron unstable. The fluctuating pressure of

hydraulic jump with low Froude Number is very complex (Zhou and Yin, 2011).

Abdel-Aal et al.,(2003) studied and developed theoretical models for the hydraulic jump as

an important method for energy dissipation to predict the depth ratios of the radial hydraulic jumps

at negative steps downstream of the control structures when the stilling basins was ended with a sill.

An experimental program was conducted to enable verification of the developed theoretical models.

Good agreement between theoretical and experimental results was obtained. The developed models

were recommended for use in the design of radial stilling basin to compute the depth ratios which

was needed to complete the dimensioning of the stilling basin.

Irzooki et al., (2005) presented a laboratory experiments to study the hydraulic performance

of stilling basin with unusual shapes of baffle blocks. Seven groups of baffle blocks were selected,

three of these groups were cut with angle (15º, 30º, 45º) horizontally, another three groups were cut

with the same above angles, but vertically, and the seventh group was cut with semi-cylindrical

section. They concluded that the cutting baffle blocks were generally better than the standard blocks

in dissipation of a hydraulic energy and reduction of a hydraulic jump length, but a ratio of drag

force applied on cutting baffle blocks was greater than this ratio on the standard blocks for the same

flow conditions and angle of cut. The cutting baffle blocks gives a greater value of the energy

dissipation which was (80.62%) than the standard blocks and greater value of reduction in the

hydraulic jump length which was(37.5%),also these blocks gives maximum increase of the drag

force ratio which was (97%) greater than its value on the standard baffle block.

Omer et al.,(2008) presented study to indicate the drag coefficient, pressure distribution and

flow types on unconventional types of angularly cut baffle blocks and compared the results with

standard baffle blocks by using the Fluent program and the experimental results. They concluded that

values of the drag coefficient for the vertically cut blocks were less than the horizontally cut baffle

blocks in the same flow conditions. Also, maximum values of applied pressures on the surface of the

vertically cut baffle blocks were less than on other models which makes them more better than

others.

Abbas,(2009) investigated an experimentally the hydraulic performance of the compound

hydraulic jump and plunge pool stilling basin operating under high head for Makhool Dam, two

series of tests were carried out; the first series are on the model as it was designed, while the second

series were on a modified model by adding two rows of chute blocks. The results indicated

that for the first model the stilling basin length can be reduced and there was negative pressure at the

beginning of the jump on the sloping apron with high turbulence and unstable water surface.

After adding the chute blocks, the tests of the second model indicated that the stilling basin length

can be reduced and all pressures were positive with reasonably stable water surface as well as lower

turbulence. Therefore, chute blocks were recommended to be added.

Retsinis et al., (2011) introduced the local change of mechanical energy within inclined

channels in sluice gate and weir flows based on experimental measurements. The dimensionless local

mechanical energy changes, in general loss for sluice gate flows and gain for weir flows were

associated to the dimensionless geometrical characteristics and angle of longitudinal slope of

channel.

Kurukji,(2012) presented an experiments to study energy dissipation for stepped spillway in

addition to the elimination of air pockets which take place at steps by using obstructions along the

edge of steps. The results of the experiments showed that the obstructions were very successful in

eliminating air pockets and had a positive effect on energy dissipation along the stepped spillway, the

results also indicated that the use o these obstructions should be started from second step until the

middle step of the spillway.

Maatooq et al.,(2013) analyzed the Diyala weir problems and compares it with the safe

limit and proposes the treatment for these problems. It was concluded that the scour occurs due to

the position of the hydraulic jump and the sequence depth of the jump was higher than the tail

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976

ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp.

water depth. Some treatment procedures

by presenting a suitable stilling basin as well as recommended to use a low weir at end of basin to

produce a back water curve that should be increase

of a hydraulic jump.

2. EXPERIMENTAL APPROACH

Experiments were carried out in the hydraulic laboratory of the civil engineering department,

college of engineering, university of Bab

rectangular open channel with dimensions of approximately 10 m long with an adjustable slope, 0.45

m deep and 0.3 m wide (as shown in figure 1).

enable visual observation of 10mm thick, and a stainless steel floor. Two movable carriages with

point gauges with accuracy of (0.5mm) were mounted on brass rails at the top of channel sides to

measure the heads over weir and downstream the hydraulic jump

tank by a centrifugal pump with a maximum capacity 40

storage tank to the flume then returns to ground tank by vertical outlet at the end of the flume. Water

discharge was measured by using flow meter. Flume bed was maintained at a horizontal slope during

all of the testing.

Figure (1)

Six sets of experiments were performed for a total of

runs was performed using a triangular cut blocks of (

jump in stilling basin with baffle blocks and end

groups of dissipation blocks (5 runs for each)

hydraulic flume operation mode and stage discharge relation

conditions were selected, and the Parameters of experiment conditions showed in table

(2) show the main details of the compound


6316(Online) Volume 5, Issue 3, March (2014), pp. 32-49 © IAEME

water depth. Some treatment procedures were suggested, these treatments cover this problem

basin as well as recommended to use a low weir at end of basin to

ould be increased the stage of tail water and ensuring the stability

EXPERIMENTAL APPROACH


college of engineering, university of Babylon. This experimental work was performed in a horizontal


m deep and 0.3 m wide (as shown in figure 1). The channel consisted of toughened glass walls

of 10mm thick, and a stainless steel floor. Two movable carriages with


measure the heads over weir and downstream the hydraulic jump. Water was supplied from a sump

tank by a centrifugal pump with a maximum capacity 40 l/sec., raising water by pump from the


ing flow meter. Flume bed was maintained at a horizontal slope during

Figure (1): Hydraulic flume used in present work

sets of experiments were performed for a total of 240 runs. The first set consisting of

triangular cut blocks of (θ=45°) to simulate a classical hydraulic

baffle blocks and end sills. Further runs consisting of (25 runs) for the rest

dissipation blocks (5 runs for each) for a particular type of compound weir. According

hydraulic flume operation mode and stage discharge relation for compound weirs

selected, and the Parameters of experiment conditions showed in table

compound weir models.


suggested, these treatments cover this problem

basin as well as recommended to use a low weir at end of basin to

the stage of tail water and ensuring the stability


This experimental work was performed in a horizontal


The channel consisted of toughened glass walls to

of 10mm thick, and a stainless steel floor. Two movable carriages with


Water was supplied from a sump

, raising water by pump from the


ing flow meter. Flume bed was maintained at a horizontal slope during

runs. The first set consisting of 30

to simulate a classical hydraulic

runs consisting of (25 runs) for the rest

weir. According to

weirs, the model test

selected, and the Parameters of experiment conditions showed in table (1).Figures



Table (1): Important characteristics of

Compound Weir Model Model

No.

Rectangular + Half Circle

Notch

Rectangular + Triangular

Notch

Rectangular + Trapezoidal

Notch

Stepped Notch

The main dimensions and specifica

table (2).Figure (3) shows the top view for basins used in this study.

Figure (2): Definition sketch showing dimensions and specifications of compound weir models (all



Important characteristics of compound weir models used in this study

Model

No.

Dimensions (cm)

Height Width Pw

1 25 20 15

2 25 10 15

3 25 20 15

4 25 11.65 15

5 25 5.0 15

5 25 5.0 15

7 25 10 15

8 25 5 15

The main dimensions and specifications of the energy dissipation blocks were presented in

the top view for basins used in this study.

Definition sketch showing dimensions and specifications of compound weir models (all

dimensions are in cm)


weir models used in this study

Weir Angle

R=10 cm

R=5 cm

θ=90°

θ=60°

θ=90°

θ=60°

2-Steps

3-Steps

tions of the energy dissipation blocks were presented in

Definition sketch showing dimensions and specifications of compound weir models (all



Table (2): Dimensions and specifications of the energy dissipation blocks used in the study

Type of

Cutting Angle

Block

Numbers Width (cm)

Triangular 8

8

Horizontal 8

8

Vertical 8

8

In order to evaluate the efficiency of the stilling basin with new types of dissipation blocks,

the experiments were conducted and the necessary measurements for each type

collected. Followed by analyzing the results and then compare it with other

the models most suitable for applicable combination

dissipation ratio and hydraulic jump lengt

(A): Triangular cut

(B): Horizontal cutting angle for dissipation blocks (60



Dimensions and specifications of the energy dissipation blocks used in the study

Dimensions

Width (cm) Length (cm) Height (cm)

5.0 8.0 3.0

5.0 8.0 3.0

5.0 8.0 3.0

5.0 8.0 3.0

5.0 8.0 3.0

5.0 8.0 3.0

evaluate the efficiency of the stilling basin with new types of dissipation blocks,

the experiments were conducted and the necessary measurements for each type of weir

analyzing the results and then compare it with other weir models to

applicable combination which represent in this research

dissipation ratio and hydraulic jump length ratio for each specific weir.

riangular cutting angle for dissipation blocks (45°, 60

°)

Horizontal cutting angle for dissipation blocks (60°, 110

°)


Dimensions and specifications of the energy dissipation blocks used in the study

Angle of

Cutting

45°

60°

60°

110°

60°

110°

evaluate the efficiency of the stilling basin with new types of dissipation blocks,

of weir notches were

models to find out

which represent in this research energy



(C): Vertical cutti

Figure (3): View pictures for basins used in this study

The general method adopted for sequencing all

same steps in each experiment by installing the dissipation bloc

certain distance between the blocks based on the recommendations of the U.S. Bureau of

Reclamation USBR (Water Measurement Manual, 2001

them on the floor of the channel at a

certain discharge, measurements were

following measurements were taken for all tests conducted on different groups of

1-Measuring the discharge passing in the channel.

2- Measure the water level over compound

3- Measure the depth of flow after hydraulic jump directly.

4- Measure the average depth of flow after the end of the hydraulic jum

5- Measure the length of the hydraulic jump (L

6- Measure the length of the hydraulic jump roller (L

Then the following calculations were

1- Calculate the initial velocity of flow (v

continuity equation:

fA

Qv ====

In which;

v= velocity of flow (L/T).

Q=discharge (L3/T).

Af=area of water way(L2).

2- Calculate the primary Froude Number

following equation:



Vertical cutting angle for dissipation blocks (60°, 110

°)

View pictures for basins used in this study

method adopted for sequencing all experiments, was performed by repeats the

same steps in each experiment by installing the dissipation blocks on a glass plate and organizes a


Water Measurement Manual, 2001) to simulate stilling basin, and then install

the floor of the channel at a distance from the nape of compound weir. Thereafter passing

were taken and new discharge was released, and so on;

following measurements were taken for all tests conducted on different groups of dispassion blocks:

easuring the discharge passing in the channel.

compound weir notch (Y1) by using point gage.

hydraulic jump directly.

Measure the average depth of flow after the end of the hydraulic jump directly (Y

Measure the length of the hydraulic jump (Lj).

Measure the length of the hydraulic jump roller (Lr).

Then the following calculations were performed:

Calculate the initial velocity of flow (v1) through weir notch and subsequent ve

….. [1]

Froude Number (Fr1), and subsequent Froude Number


was performed by repeats the

ks on a glass plate and organizes a


to simulate stilling basin, and then install

Thereafter passing a

new discharge was released, and so on; the

dispassion blocks:

p directly (Y2).

) through weir notch and subsequent velocity (v2) via

Froude Number (Fr2) from the



38

gD

vFr ==== ….. [2]

In which;

g= the acceleration due to gravity (L/T2).

D=hydraulic depth (L).

3- Based on energy relationships, the general relationship for the flow energy dissipation can be

verified, applying energy equations between two sections upstream and downstream weir, we get:

g

vYE

2

2

111 ++++==== ….. [3]

g

vYE

2

2

222 ++++==== ….. [4]

In which;

E1= flow energy upstream weir (L).

E2= flow energy downstream hydraulic jump (L).

v1,v2= velocity upstream weir and downstream hydraulic jump respectively (L/T).

Y1=water depth over weir notch (L).

Y2=water depth downstream hydraulic jump (L).

3. RESULTS AND DISCUSSION

3.1 Effect of Using Energy Dissipation Blocks on the Relative Energy Dissipation The results concerning the energy dissipation ratio (E2/E1) were plotted against primary

Froude Number (Fr1) for all compound weir notches used in the present study, as shown in figures

(4-11). Figure (4) shows the obtained energy dissipation ratio (E2/E1) computed at downstream of the

hydraulic jump for different types of energy dissipation blocks for compound weirs of half circle

lower notch (radius of 10cm).The obtained relative energy dissipation ratio varies between

(64.574%) at maximum discharge of (11.20ℓ�� and (66.418%) at minimum discharge of (3.0 ℓ��

for triangular cutting block with (θ=45°). The relative energy dissipation ratio (E2/E1) increased as

(Fr1) increased roughly for all types of dissipation blocks.

Figure (5) shows that largest average value for (E2/E1) was (62.172%) when using a

triangular cut blocks of (θ=45°) for all discharge values between (3.80 to 11.11 ℓ��). Whereas the

relative energy dissipation ratio (E2/E1) decreased rapidly for increased (Fr1), almost for all types of

energy dissipation blocks, this was due to high turbulence and eddies were clear at the basin bed and

the flow surface, especially at high discharges when using horizontal and vertical cut angle blocks

were much higher compared to that of triangular cut blocks.



39

Figure (4): Energy dissipation ratio for compound weir having (R=10cm) lower half-circle

notch

Figure (5): Energy dissipation ratio for compound weir having (R=5cm) lower half-circle notch

Figures (6&7) summarizes the obtained values of the relative energy dissipation ratio (E2/E1)

and Froude Number (Fr1) for compound weir having (60°) and (90°) lower V-notches respectively.

The relative energy dissipation ratio (E2/E1) was decreased rapidly with a small difference versus the

increase of (Fr1) for the initial discharge rates (i.e., Fr1 values between 0.5 to 1.0) for the weir having

lower V-notch (60°), whereas (E2/E1) values were increased significantly when (Fr1) was increased

beyond prescribed range. The minimum average value of (E2/E1) was (44.519%) which was recorded

for a blocks of vertical angle of (θ=60°) as shown in figure (6). For all applied discharge values, the

relative energy dissipation ratio (E2/E1) was decreased as (Fr1) increased (see figure 7), the average

value of (E2/E1) was about (59.167%-55.793%) for all blocks types with a reduction of (E2/E1)

average values of (13.435%-11.274%) for compound weir having(90°) lower V-notch.

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6

Fr1

50

55

60

65

70

75

80

85

E2

/E1

Energy Dissipation Blocks

θ=60

θ=45

θ=60

θ=110

θ=60

θ=110

Triangular CutBlocks

Horizontal AngleBlocks

Vertical AngleBlocks

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

Fr1

40

45

50

55

60

65

70

75

80

E2

/E1


θ=60

θ=45

θ=60

θ=110

θ=60

θ=110






40

Figure (6): Energy dissipation ratio for compound weir having 60° lower V-notch

Figure (7): Energy dissipation ratio for compound weir having 90° lower V-notch

Figures (8&9) show the variation of the relative energy dissipation ratio (E2/E1) and the

primary Froude Number with the applied discharges for compound weir having (30°) and (90°)

lower trapezoidal notches respectively. Figure (8) indicates there was a slight decreasing for high

discharges. On the other hand, there was no clear change in relative energy dissipation ratio (E2/E1)

between different configurations of blocks especially at the low discharges, i.e., the average value of

(E2/E1) was about (53.943%-51.056%) for all blocks types. Figure (9) shows that flow through

compound weir having (90°) lower trapezoidal notch, and along dissipation blocks during the

experimental runs at the same discharges have the same hydraulic characteristics of the flow that was

described for figure(8) above. But with high rate of energy dissipation ratio (E2/E1) which was about

(70.228%) at the maximum discharge of (11.0 ℓ��.

0.45 0.60 0.75 0.90 1.05 1.20 1.35 1.50Fr1

30

35

40

45

50

55

60

65

70

E2/E

1


θ=60

θ=45

θ=60

θ=110

θ=60

θ=110

Triangular Cut Blocks

Horizontal Angle Blocks


0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60Fr1

40

45

50

55

60

65

70

75

80

85

90

E2/E

1


θ=60

θ=45

θ=60

θ=110

θ=60

θ=110






41

Figure (8): Energy dissipation ratio for compound weir having 30° lower trapezoidal notch

Figure (9): Energy dissipation ratio for compound weir having 90° lower trapezoidal notch

Figures (10&11) show the variation of the relative energy dissipation ratio (E2/E1) and the

primary Froude Number with the applied discharges for compound weir having (2-steps) and (3-

steps) lower notches respectively. The obtained values of (E2/E1) at high discharge with (2-steps)

compound weir were less than that of smaller discharges for all blocks configurations. The maximum

(E2/E1) of (68.859%) for a blocks of triangular cut with angle (θ=60°). While, for the rest blocks

configurations there were a slight differences at all discharges values with a relative difference of

about 1.46 % as shown in figure (10). The relative energy dissipation ratio (E2/E1) versus Froude

Number (Fr1) during the experimental runs at all applied discharges for (3-steps) compound weir was

shown in figure (11), the average values of (E2/E1) were about (62.289%) for a blocks of triangular

cut with (θ=45°) to (59.884%) for a block of vertical angle with(θ=60

°).

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2Fr1

40

45

50

55

60

65

70

75

80

85

E2/E

1


θ=60

θ=45

θ=60

θ=110

θ=60

θ=110




0.4 0.6 0.8 1.0 1.2 1.4 1.6

Fr1

15

25

35

45

55

65

75

E2/E

1


θ=60

θ=60

θ=60

θ=110

θ=60

θ=110






42

Figure (10): Energy dissipation ratio for compound weir having (2-steps) lower notch

Figure (11): Energy dissipation ratio for compound weir having (3-steps) lower notch

3.2 Effect of Using Energy Dissipation Blocks on the Hydraulic Jump and Roller Length To investigate the effects of using the energy dissipation blocks upon the hydraulic jump

location, relative reduction in hydraulic jump length, and length of roller (or recirculation zone) of

hydraulic jump for all compound weir notches used in the present study, the results obtained herein

were plotted as shown in figures (12-19). Figure (12) shows that minimum average value for relative

hydraulic jump length (Lj/Y2) was (5.271) when using a blocks of triangular cut of (θ=45°) for all

discharge values between (3.0 to11.2 ℓ��). The relative hydraulic jump length (Lj/Y2) increases

slightly as Froude Number (Fr1) increases for all types and configurations of energy dissipation

blocks when using the compound weir having (R=10cm) lower half-circle notch. . Figure (13) shows

that at maximum applied discharge, the hydraulic jump was formed at shorter distance from the

compound weir having (R=5cm) lower half-circle notch with (Lj/Y2) of (5.191) when using blocks of

triangular cut with (θ=45°), while for vertical angle cut with (θ=60

°) the hydraulic jump was formed

0.7 0.8 0.9 1.0 1.1 1.2 1.3

Fr1

48

51

54

57

60

63

66

69

E2

/E1


θ=60

θ=45

θ=60

θ=110

θ=60

θ=110




0.6 0.7 0.8 0.9 1.0 1.1 1.2

Fr1

60.0

63.0

66.0

69.0

72.0

75.0

78.0

E2

/E1


θ=60

θ=45

θ=60

θ=110

θ=60

θ=110






43

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4

Fr1

0

5

10

15

20

25

30

35

Lj/

Y1


θ=60

θ=45

θ=60

θ=110

θ=60

θ=110




at longer distance from the weir with (Lj/Y2) of (16.125). For all types of dissipation blocks the

(Lj/Y2) decreases as (Fr1) increased within the range of applied discharges.

Figure (12): Hydraulic jump length ratio for compound weir having (R=10cm) lower half-circle

notch

Figure (13): Hydraulic jump length ratio for compound weir having (R=5cm) lower half-circle notch

Figure (14) shows the variation of relative hydraulic jump length (Lj/Y2) and the Froude

Number (Fr1) with applied discharge for a compound weir having (60°) lower V-notch, (Lj/Y2) was

decreased significantly versus the increase of (Fr1) for values between (0.4 to 1.0), whereas (Lj/Y2)

values increased when (Fr1) was increased for higher discharge values. The hydraulic jump was

occurred at shorter distance from the compound weir when the value of (Lj/Y2) was (5.359) which

recorded for a blocks of triangular cut with angle of (θ=45°). For all applied discharge values, the

relative hydraulic jump length (Lj/Y2) were decreased as (Fr1) increased as shown in figure (15), the

shortest and longest distance in which the hydraulic jump formed within stilling basin length were

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

Fr1

0

3

6

9

12

15

18

21

24

27

30

33

Lj/

Y1


θ=60

θ=45

θ=60

θ=110

θ=60

θ=110






44

about (4.794) for a blocks of triangular cut angle with (θ=45°) and (8.917) for a blocks of horizontal

cut angle with (θ=110°) respectively.

Figure (14): Hydraulic jump length ratio for compound weir having 60° lower V-notch

Figure (15): Hydraulic jump length ratio for compound weir having 90° lower V-notch

Figures (16 & 17) show the variation of the relative hydraulic jump length (Lj/Y2) and the

Froude Number(Fr1) with the all applied discharge range for compound weir having (30°) and (90°)

lower trapezoidal notches respectively. Figure (16) shows there was a rapidly decreasing in (Lj/Y2)

as (Fr1) increase within the limits of lower and moderate flow rates for all blocks types. There were

small differences in relative energy dissipation ratio (Lj/Y2) between various configurations of blocks

especially at the low discharges; the average value of (Lj/Y2) was about (6.314) for a blocks of

triangular cut angle with (θ=45°) to (8.616) for a blocks of horizontal angle with (θ=110

°).

0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9

Fr1

2

4

6

8

10

12

14

16

Lj/

Y1

Energy Dissipation locks

θ=60

θ=45

θ=60

θ=110

θ=60

θ=110



Vertical Angle Blocks

0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70

Fr1

2.0

3.5

5.0

6.5

8.0

9.5

11.0

12.5

14.0

15.5

Lj/

Y1

Energy Dissipation locks

θ=60

θ=45

θ=60

θ=110

θ=60

θ=110






45

Figure (16): Hydraulic jump length ratio for compound weir having (30°) lower trapezoidal notch

Figure (17) shows that flow through compound weir having (90°) lower trapezoidal notch,

it’s clear that (Lj/Y2) decreased as (Fr1) increase within applied discharge range for all blocks types

used in the present study, maximum reduction in relative hydraulic jump length (Lj/Y2) of (5.916)

occurred when using a blocks of triangular cut with (θ=60°), while the minimum reduction of (8.698)

for a blocks of vertical cut angles with (θ=60°). Generally, there were slight differences on the

reduction of relative hydraulic jump length (Lj/Y2) at low discharges for all blocks types and

configurations.

Figure (17): Hydraulic jump length ratio for compound weir having (90°) lower trapezoidal notch

Figures (18 & 19) show the variation of the relative hydraulic jump length (Lj/Y2) and the

Froude Number (Fr1) with the all applied discharge range for compound weir having (2-steps) and

(3-steps) lower notches respectively. From figure (18) it is clear that relative hydraulic jump length

(Lj/Y2) decreases significantly as Froude Number (Fr1) decreases for all blocks types. At maximum

0.40 0.55 0.70 0.85 1.00 1.15 1.30 1.45 1.60

Fr1

0

2

4

6

8

10

12

14

16

18

Lj/

Y2


θ=60

θ==45

θ=60

θ=110

θ=60

θ=110



VerticalAngle Blocks

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2

Fr1

0

2

4

6

8

10

12

14

16

18

Lj/

Y2


θ=60

θ==45

θ=60

θ=110

θ=60

θ=110



VerticalAngle Blocks



46

applied discharge of (10.5ℓ��), the relative hydraulic jump length (Lj/Y2) was (12.576) for a blocks

of vertical cut angle with (θ=60°), with a free hydraulic jump at a distance (83.0 cm) forward the

weir. The shortest average value of (Lj/Y2) of (5.374) formed when using blocks of triangular cut

angle with (θ=60°).

Figure (18): Hydraulic jump length ratio for compound weir having (2-steps) lower notch

Figure (19) makes clear that for a compound weir having (3-steps) lower notch, the (Lj/Y2)

decreased slightly as (Fr1) increased, and occurred through all applied discharges range. The

hydraulic jump occurs at shorter distances measured from the compound weir when using blocks of

triangular cut angle with (θ=45°) in which the average value of (Lj/Y2) was (5.933).

Figure (19): Hydraulic jump length ratio for compound weir having (3-steps) lower notch

0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3

Fr1

0

2

4

6

8

10

12

14

16L

j/Y

1Energy Dissipation Blocks

θ=60

θ=45

θ=60

θ=110

θ=60

θ=110




0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25

Fr1

0

2

4

6

8

10

12

14

16

18

20

Lj/

Y1


θ=60

θ=45

θ=60

θ=110

θ=60

θ=110






Figures (20-22) show the flow through the compound weir models and along the various

configurations of energy dissipation blocks, and the hydraulic jump formation d

experimental runs at the applied discharges. High eddies and air entrainment occurred at the bed of

channel when the energy dissipaters were used especially at high discharges. Then, more energy will

be dissipated. A free hydraulic jump was form

distance according to the flow rate and the configuration. The hydraulic jump occurs at shorter

distances measured from the weir front when using energy dissipation blocks in all of the applied

discharges. Table (3) summarizes the average values of the primary Froude Number (Fr

relative jump roller length (Lr/∆Y) that were obtained at the applied discharge range.

(a) Arrangement of blocks with horizontal

cut angle

Figure (20): Flow along dissipation blocks for compound weir having half circle lower notch

(a) Arrangement of blocks with triangular

cut angle

Figure (21): Flow along dissipation blocks for compound weir having stepped lower notch



) show the flow through the compound weir models and along the various

configurations of energy dissipation blocks, and the hydraulic jump formation d



be dissipated. A free hydraulic jump was formed at the downstream of the weir at a different



(3) summarizes the average values of the primary Froude Number (Fr

Y) that were obtained at the applied discharge range.

horizontal (b) Arrangement of blocks with vertical

cut angle

Flow along dissipation blocks for compound weir having half circle lower notch

(a) Arrangement of blocks with triangular (b) Arrangement of blocks with vertical

cut angle

Flow along dissipation blocks for compound weir having stepped lower notch


) show the flow through the compound weir models and along the various

configurations of energy dissipation blocks, and the hydraulic jump formation during the



ed at the downstream of the weir at a different



(3) summarizes the average values of the primary Froude Number (Fr1), and

Y) that were obtained at the applied discharge range.

blocks with vertical

angle

Flow along dissipation blocks for compound weir having half circle lower notch

nt of blocks with vertical

Flow along dissipation blocks for compound weir having stepped lower notch



(a) Arrangement of blocks with horizontal

cut angle

Figure (22): Flow along dissipation blocks for compound weir having lower V

Table (3): Summary of obtained average values of (Fr

configurations used in this study

Type of Dissipation Blocks

Blocks of triangular cut angle: Configuration(A):

θ=45°

Configuration(B):

θ=60°

Rectangle with lower

half circle notch

Rectangle with lower V

notch


trapezoidal notch

Rectangle with stepped

lower notch

Blocks of horizontal cut

angle:

Configuration(A): θ=60°

Configuration(B): θ=110°


half circle notch


notch

Rectangle wi

trapezoidal notch


lower notch

Blocks of vertical cut angle:

Configuration(A): θ=60°

Configuration(B): θ=110°


half circle notch


notch


trapezoidal notch


lower notch



(a) Arrangement of blocks with horizontal (b) Arrangement of blocks with vertical

cut angle

Flow along dissipation blocks for compound weir having lower V

Summary of obtained average values of (Fr1), and roller length (Lr/∆Y) for all blocks and

configurations used in this study

Weir Model

(θw= Weir angle)

Discharge

Range

( )

(Fr1

(A)


half circle notch R=5,10cm

3.1-11.9 0.80 0.78

3.1-11.9 1.17 1.08

Rectangle with lower V-θθθθw=60

°°°°, 90°°°° 3.1-11.1 0.82 0.84

3.3-11.1 0.46 0.50


ezoidal notch θθθθw=30

°°°°, 90°°°°

3.1-11.1 0.67 0.74

3.2-11.6 0.67 0.74


lower notch 2,3 steps

3.3-10.5 0.79 0.83

2.9-11.6 0.85 0.87



3.1-11.9 1.32 1.14

3.1-11.9 1.13 1.08


°°°°, 90°°°° 3.1-11.1 1.07 1.15

3.3-11.1 0.50 0.49


trapezoidal notch θθθθw=30°°°°, 90°°°°

3.1-11.1 0.66 0.68

3.2-11.6 0.75 0.67



3.3-10.5 0.82 0.87

2.9-11.6 0.94 0.93



3.1-11.9 1.42 1.16

3.1-11.9 1.24 1.09


°°°°, 90°°°° 3.1-11.1 0.86 0.92

3.3-11.1 0.46 0.44


trapezoidal notch θθθθw=30

°°°°, 90°°°°

3.1-11.1 0.69 0.78

3.2-11.6 0.58 0.71



3.3-10.5 0.82 0.84

2.9-11.6 0.94 0.93


nt of blocks with vertical

Flow along dissipation blocks for compound weir having lower V- notch

Y) for all blocks and

1) (Lr/∆∆∆∆Y)

(B) (A) (B)

0.78 5.26 5.02

1.08 8.60 6.52

0.84 2.01 1.98

0.50 3.21 3.03

0.74 2.78 3.32

0.74 5.95 5.94

0.83 7.24 10.47

0.87 5.18 5.70

1.14 8.63 8.80

1.08 8.63 9.16

1.15 2.22 2.19

0.49 3.40 3.67

0.68 3.40 3.73

0.67 7.50 7.96

0.87 7.31 9.04

0.93 5.78 6.59

1.16 11.62 10.01

1.09 13.02 10.29

0.92 2.58 2.57

0.44 4.03 3.39

0.78 3.38 3.67

0.71 6.18 7.72

0.84 8.26 8.43

0.93 6.27 6.84



49

4. CONCLUSIONS

Based on the results obtained in this study, the following conclusions were achieved:

1- Arrangement containing the use of compound weir with (60°) lower V-notch and dissipation

blocks of horizontal cutting angle configurations (60°,110

°)were produced maximum reduction in

flow energy of (54.7% to 55.4%) respectively for all the applied range of discharge.

2- Configuration included use of compound weir with (60°) lower V-notch and dissipation blocks of

triangular cutting angle configurations (45°,60

°) have the smallest value of the relative hydraulic

jump length (Lj/Y2) of (5.36 to6.02) respectively for all the applied range of discharge compared

with configurations in this study.

3- The relative jump roller length (recirculation zone), with above configuration was about (1.94) at

minimum applied discharge of (3.2ℓ��), and was about (2.14) at maximum applied discharge of

(10.3 ℓ��) for blocks of triangular cut angle with (θ=60°).

4- The obtained results indicate that use the configuration containing compound weir with (60°, 90

°)

lower V-notch with all dissipation blocks have a high efficiency especially at the high discharges.

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20320140503004

Technology

energy of flow

specific energy

reduction of hydraulic

forced hydraulic jump

energy dissipation rate

flow energy dissipater

effect of dissipation

radial hydraulic jumps