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

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EXPERIMENT # 03

TO STUDY THE FLOW CHARACTERISTICS OVER THE HUMP ORWEIR IN

A RECTANGULAR CHANNEL

OBJECTIVE

::

To study the variation of flow with the

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

APPARATUS :

S6 tilting flume apparatus which consists of : S6 tilting flume apparatus which consists of :



 OrificeOrifice



 Differential manometerDifferential manometer

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 Large chamber to study flowLarge chamber to study flow

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 Controlling meter to vary slope.Controlling meter to vary slope.

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 Hook gauge/point gauge to measure the depthHook gauge/point gauge to measure the depth

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 Broad crested weirs:Broad crested weirs:

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 Rounded corner weirRounded corner weir

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 Sharp corner weirSharp corner weir

RELATED THEORY:

HUMP:

Stream lined construction over the bed of

Stream lined construction over the bed of a channel is called a channel is called hump.hump. OR

OR

The raised bed of the channel at a certain location is called as hump. The raised bed of the channel at a certain location is called as hump.

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Since the flow is

Since the flow is subcritical, the water surface will drop due subcritical, the water surface will drop due to a decrease in to a decrease in the specific energy.In abovethe 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 Fig the water surface which was at P at section 1 will come down to point R at section 2. Thedepth y22

will be give by will be give by

E = y

2 +



_





=

= y

y

2

+











_



SUPERCRITICAL

SUPERCRITICAL FLOW

FLOW ::

If Y

If Y11is in the supercritical flow regime, Fig below shows that the depth of is in the supercritical flow regime, Fig below shows that the depth of flow increases due to theflow increases due to the

reduction of specific energy. Point P`

reduction of specific energy. Point P` corresponds to ycorresponds to y11and point R` to depth at the section 2. Up to theand point R` to depth at the section 2. Up to the

critical depth, y

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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 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 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 acertain amount as there is a slight depression in the water.Further increase in the height of hump will create more

create more depression of water depression of water surface over the surface over the hump untilfinally the depth becomes hump untilfinally the depth becomes equals toequals to the critical depth. When the hump height will be equal to the criticaldepth then there will be critical flow 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 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 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

increased. This phenomenon is referred to as damming action.damming action.

CRITICAL HUMP HEIGHT :

Is the minimum hump height that can cause the

Is the minimum hump height that can cause the critical depth over the hump iscalled as critical humpcritical depth over the hump iscalled as critical hump height. height.

CASE 1

  yy11= y= y00   yy11> y> y22   yy11,y,y22 > y> y00 

 The flow conditions will be sub criticalThe flow conditions will be sub critical



 Upstream level increases Over humpUpstream level increases Over hump



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CASE 3:

  yy11> y> y00   yy22= y= ycc   yy11> y> ycc   yy33< y< ycc

DAMMING ACTION:

It is the

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

PROCEDURE

:: 1.Fix the slope of the 1.Fix the slope of the flumeflume

2.Introduce a round corner wide crested

2.Introduce a round corner wide crested weir in the flume at certain weir in the flume at certain locationlocation 3.Set the discharge in the

3.Set the discharge in the flume having certain value.flume having certain value. 4.Note depth of flow at

4.Note depth of flow at upstream side of hump, over the hump and downstream side of upstream side of hump, over the hump and downstream side of hump atcertainhump atcertain point.

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OBSERVATION & CALCULATION

WIER TYPE

WIER TYPE HEIGHTHEIGHT_(mm)_(mm) WIDTH (mm)WIDTH (mm)

ROUND CORNER ROUND CORNER 120 120 400400 SHARP SHARP CORNER CORNER 60 60 400400 ss rr .. # # WIER WIER TYPE TYPE Q Q q q yycc

U/S DEPTH OF FLOW

U/S DEPTH OF FLOW OVER THE HUMP DEPTH OFOVER THE HUMP DEPTH OF FLOW

FLOW D/S D/S DEPTH DEPTH OF OF FLOW FLOW TYPE TYPE OF OF FLOWFLOW y

y11 yy22 yy33 yyavgavg yy11 yy22 yy33 yyavgavg yy11 yy22 yy33 yyavgavg U/SU/S

OVER OVER HUMP HUMP D/SD/S

m3/sec

m3/sec m3/secm3/sec

/m /m mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mmmm x=4 x=4 m m x=4.6 x=4.6 m m x=5.2 x=5.2 m m x=5.4 x=5.4 m m x=5.5 x=5.5 m m x x=5.65=5.65 m m x=5.85 x=5.85 m m x=6.1 x=6.1 m m x=6.3 x=6.3 m m 1 1 SHARP SHARP CORNER CORNER 0.008 0.027 41.69

0.008 0.027 41.69 124.4 124.4 122.3 122.3 121.6 121.6 122.77 122.77 97 97 95 95 94.5 94.5 95.50 95.50 21.2 21.2 19.4 19.4 19.1 19.1 19.9019.90 SUBSUB_CR_CR SUBSUB_CR_CR SUPERSUPER_CR._CR. 2

2 0.009 0.009 0.031 0.031 46.36 46.36 130.6 130.6 128.2 128.2 127.8 127.8 128.87 128.87 99 99 97.4 97.4 95.6 95.6 97.33 97.33 21.9 21.9 20 20 19.7 19.7 20.5320.53 SUBSUB_CR_CR SUBSUB_CR_CR SUPERSUPER_CR._CR. 3 3 0.011 0.011 0.037 0.037 51.41 51.41 135.8 135.8 135 135 134.5 134.5 135.10 135.10 105 105 101.5 101.5 100 100 102.17 102.17 24.4 24.4 22 22 27 27 24.4724.47 SUBSUB CR CR SUB SUB CR CR SUPER SUPER CR. CR. 1 1 ROUNF ROUNF CORNER CORNER 0.007 0.007 0.023 0.023 37.87 37.87 179 179 179 179 179 179 179.00 179.00 159.5 159.5 158.7 158.7 146.9 146.9 155.03 155.03 28.7 28.7 25.4 25.4 17.9 17.9 24.0024.00 SUBSUB CR CR SUB SUB CR CR SUPER SUPER CR. CR. 2

2 0.009 0.009 0.030 0.030 44.91 44.91 183.1 183.1 183.1 183.1 183.1 183.1 183.10 183.10 163.5 163.5 158 158 144.9 144.9 155.47 155.47 17.2 17.2 15 15 16.6 16.6 16.2716.27 SUBSUB_CR_CR SUBSUB_CR_CR SUPERSUPER_CR._CR. 3 3 0.017 0.017 0.057 0.057 68.81 68.81 215.8 215.8 215.8 215.8 215.4 215.4 215.67 215.67 192 192 179.7 179.7 160.8 160.8 177.50 177.50 30.6 30.6 30 30 31 31 30.5330.53 SUBSUB CR CR SUB SUB CR CR SUPER SUPER CR. CR.

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0 0 0.02 0.02 0.04 0.04 0.06 0.06 0.08 0.08 0.1 0.1 0.12 0.12 0.14 0.14 4 4 44..55 55 55..55 66 66..55 W W A A T T E E R R D D E E P P T T H H ( ( m m m m ) ) HORIZONTAL DISTANCE (m) HORIZONTAL DISTANCE (m) Q=0.009378m Q=0.009378m33_/sec_/sec

SHARP CORNER BROAD CRESTED WIER

0 0 0.02 0.02 0.04 0.04 0.06 0.06 0.08 0.08 0.1 0.1 0.12 0.12 0.14 0.14 4 4 44..55 55 55..55 66 66..55 W W A A T T E E R R D D E E P P T T H H ( ( m m m m ) ) HORIZONTAL DISTANCE (m) HORIZONTAL DISTANCE (m) Q=0.007998m Q=0.007998m33_/sec_/sec

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0 0 0.02 0.02 0.04 0.04 0.06 0.06 0.08 0.08 0.1 0.1 0.12 0.12 0.14 0.14 0.16 0.16 4 4 44..55 55 55..55 66 66..55 W W A A T T E E R R D D E E P P T T H H ( ( m m m m ) ) HORIZONTAL DISTANCE (m) HORIZONTAL DISTANCE (m)

Q=0.010952m

33

_/sec

0 0 0.02 0.02 0.04 0.04 0.06 0.06 0.08 0.08 0.1 0.1 0.12 0.12 0.14 0.14 0.16 0.16 0.18 0.18 0.2 0.2 4 4 44..55 55 55..55 66 66..55 W W A A T T E E R R D D E E P P T T H H ( ( m m m m ) ) HORIZONTAL DISTANCE (m) HORIZONTAL DISTANCE (m)

Q=0.006926m

33

_/sec

ROUND CORNER BROAD CRESTED WIER

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0 0 0.02 0.02 0.04 0.04 0.06 0.06 0.08 0.08 0.1 0.1 0.12 0.12 0.14 0.14 0.16 0.16 0.18 0.18 0.2 0.2 4 4 44..55 55 55..55 66 66..55 W W A A T T E E R R D D E E P P T T H H ( ( m m m m ) ) HORIZONTAL DISTANCE (m) HORIZONTAL DISTANCE (m)

Q=0.008942m

33

_/sec

0 0 0.02 0.02 0.04 0.04 0.06 0.06 0.08 0.08 0.1 0.1 0.12 0.12 0.14 0.14 0.16 0.16 0.18 0.18 0.2 0.2 0.22 0.22 0.24 0.24 4 4 44..55 55 55..55 66 66..55 W W A A T T E E R R D D E E P P T T H H ( ( m m m m ) ) HORIZONTAL DISTANCE (m) HORIZONTAL DISTANCE (m)

Q=0.016961m

33

_/sec

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COMMENTS :

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 The flow is The flow is subcritical subcritical in both cases at in both cases at upstream side .upstream side .

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 The flow is The flow is subcritical subcritical in both cases over in both cases over the hump .the hump .

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