To Study the Flow Characteristics Over the Hump Orweir in a Rectangular Channel

[FAISAL SARDAR]

2009-CIV-122

EXPERIMENT # 03 TO STUDY THE FLOW CHARACTERISTICS OVER THE HUMP ORWEIR IN A RECTANGULAR CHANNEL

OBJECTIVE: To study the variation of flow with the introduction of different types of weirs in the flume.

APPARATUS : S6 tilting flume apparatus which consists of :  Orifice  Differential manometer  Large chamber to study flow  Controlling meter to vary slope.  Hook gauge/point gauge to measure the depth  Broad crested weirs:  Rounded corner weir  Sharp corner weir

RELATED THEORY: HUMP: Stream lined construction over the bed of a channel is called hump. OR The raised bed of the channel at a certain location is called as hump.

[FAISAL SARDAR]

2009-CIV-122

Since the flow is subcritical, the water surface will drop due to a decrease in the specific energy.In above Fig the water surface which was at P at section 1 will come down to point R at section 2. Thedepth y 2 will be give by

E = y2 +

  

= y2 +

    

SUPERCRITICAL FLOW : If Y1 is in the supercritical flow regime, Fig below shows that the depth of flow increases due to the reduction of specific energy. Point P` corresponds to y1and point R` to depth at the section 2. Up to the critical depth, y2 increases to reach yc at ΔZ = ΔZmax. For ΔZ > ΔZmax, the depth over the hump y2= yc

[FAISAL SARDAR]

2009-CIV-122

EFFECT OF HUMP HEIGHT ON THE DEPTH OF FLOW: Height of hump is less than critical hump height then there will be sub critical flow over the hump,downstream of the hump and upstream of the hump. Depth of flow over the hump will decrease by acertain amount as there is a slight depression in the water.Further increase in the height of hump will create more depression of water surface over the hump untilfinally the depth becomes equals to the critical depth. When the hump height will be equal to the criticaldepth then there will be critical flow over the hump, sub critical on the upstream side and super critical just downstream of the hump.If the hump is made still higher, critical depth will maintain over the hump and depth on upstream sidewill be increased. This phenomenon is referred to as damming action.

CRITICAL HUMP HEIGHT : Is the minimum hump height that can cause the critical depth over the hump iscalled as critical hump height.

CASE 1      

y1 = y0 y1 > y2 y1,y2 > y0 The flow conditions will be sub critical Upstream level increases Over hump At downstream depth is recovered after a long distance

[FAISAL SARDAR]

2009-CIV-122

CASE 3:    

y1 > y0 y2 = yc y1 > yc y3 < yc

DAMMING ACTION: It is the sudden increase of the water depth at upstream side due to increase in hump height.

PROCEDURE: 1.Fix the slope of the flume 2.Introduce a round corner wide crested weir in the flume at certain location 3.Set the discharge in the flume having certain value. 4.Note depth of flow at upstream side of hump, over the hump and downstream side of hump atcertain point.

[FAISAL SARDAR ]

2009-CIV-122

OBSERVATION & CALCULATION

s r . #

WIER TYPE

HEIGHT (mm)

WIDTH (mm)

ROUND CORNER

120

400

SHARP CORNER

60

400

WIER TYPE

U/S DEPTH OF FLOW Q

m3/sec

q m3/sec  /m

yc

mm

OVER THE HUMP DEPTH OF FLOW

D/S DEPTH OF FLOW

y1

y2

y3

yavg

y1

y2

y3

yavg

y1

y2

y3

yavg

mm

mm

mm

mm

mm

mm

mm

mm

mm

mm

mm

mm

x=4 m

x=4.6

m

x=5.2 m

x=5.4 m

x=5.5 m

x=5.65 m

x=5.85 m

x=6.1 m

x=6.3 m

TYPE OF FLOW U/S

OVER HUMP

D/S

0.008

0.027

41.69

124.4

122.3

121.6

122.77

97

95

94.5

95.50

21.2

19.4

19.1

19.90

SUB CR

SUB CR

SUPER CR.

0.009

0.031

46.36

130.6

128.2

127.8

128.87

99

97.4

95.6

97.33

21.9

20

19.7

20.53

SUB CR

SUB CR

SUPER CR.

3

0.011

0.037

51.41

135.8

135

134.5

135.10

105

101.5

100

102.17

24.4

22

27

24.47

SUB CR

SUB CR

SUPER CR.

1

0.007

0.023

37.87

179

179

179

179.00

159.5

158.7

146.9

155.03

28.7

25.4

17.9

24.00

SUB CR

SUB CR

SUPER CR.

0.009

0.030

44.91

183.1

183.1

183.1

183.10

163.5

158

144.9

155.47

17.2

15

16.6

16.27

SUB CR

SUB CR

SUPER CR.

0.017

0.057

68.81

215.8

215.8

215.4

215.67

192

179.7

160.8

177.50

30.6

30

31

30.53

SUB CR

SUB CR

SUPER CR.

1 2

2 3

SHARP CORNER

ROUNF CORNER

[FAISAL SARDAR ]

2009-CIV-122

SHARP CORNER BROAD CRESTED WIER Q=0.007998m3 /sec W A T E R D E P T H

0.14 0.12     (       

m m

    )       

0.1 0.08 0.06 0.04 0.02 0 4

4.5

5

5.5

6

6.5

HORIZONTAL DISTANCE (m)

Q=0.009378m3 /sec W A T E R

0.14 0.12 0.1     (       

m 0.08 D m 0.06 E P 0.04 T 0.02 H     )       

0 4

4.5

5

HORIZONTAL DISTANCE (m)

5.5

6

6.5

[FAISAL SARDAR ]

2009-CIV-122

Q=0.010952m3 /sec 0.16

W A T E R D E P T H

0.14 0.12     (       

0.1

m 0.08 m 0.06

    )       

0.04 0.02 0 4

4.5

5

5.5

6

6.5

HORIZONTAL DISTANCE (m)

ROUND CORNER BROAD CRESTED WIER Q=0.006926m3 /sec 0.2 0.18 0.16 0.14 0.12 0.1 m 0.08 m 0.06 D 0.04 E 0.02 P 0 T

W A T E R

    (       

    )       

H

4

4.5

5

HORIZONTAL DISTANCE (m)

5.5

6

6.5

[FAISAL SARDAR ]

2009-CIV-122

Q=0.008942m3 /sec 0.2

W A T E R D E P T H

0.18 0.16 0.14     (       

0.12

m 0.1 m 0.08

    )       

0.06 0.04 0.02 0 4

4.5

5

5.5

6

6.5

5.5

6

6.5

HORIZONTAL DISTANCE (m)

Q=0.016961m3 /sec 0.24 0.22 0.2 0.18 0.16 0.14 0.12 m 0.1 m 0.08 D 0.06 E 0.04 P 0.02 T 0

W A T E R

    (       

    )       

H

4

4.5

5

HORIZONTAL DISTANCE (m)

[FAISAL SARDAR ]

2009-CIV-122

COMMENTS : 

The flow is subcritical in both cases at upstream side .  The flow is subcritical in both cases over the hump .  The flow is supercritical in both cases at downstream side immediately after the wier .