notches and weir

Name Enrollment No.

Gandhi Harshil Rajubhai 141100106018

Deshmukh Bhavik Hasmukhlal 15DTOD002

Kotila Jayveer Vanrajbhai 15DTOD007

Mistry Aditya Pramodbhai 15DTOD008

Pandya Dhrumil Dipakbhai 15DTOD009

Subject:- Fluid MechanicsSubject code:- 2130602Guided by:- Asst.Prof.Nilesh Rathod

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OUTLINENotch Types of NotchWeirTypes of weirDifference between Notch & Weir

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NotchA notch may be defined as an opening provided in one side of a tank or a reservoir, with upstream liquid level below the top edge of the opening.A notch may have only the bottom edge and sides.The bottom edge of north over which the liquid is flow is known as sill or crest.The sheet of liquid flowing over a notch is known as nappe or vein.A notch is usually made of a metallic plate.A notch is used to measure discharge of a small stream or canal.

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Types of Notch

1)Rectangular notch2)Triangular notch (V-notch)3)Trapezoidal notch4)Stepped notch

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Discharge over a Rectangular notchConsider a rectangular notch

in one side of a tank over which is flowing.

It gives less accuracy.The equation of Discharge

over a Rectangular notch Q= .Cd. L.⅔ √(2g).H^(3/2)

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Discharge over a triangular NotchA triangular notch is also called a

V-notch.Consider a triangular notch, in

one side of a tank, over which water is flowing.

It gives more accuracy when discharge charge is small.

For 90° notch, the equation is simple.

It requires only readings of H, to find discharge.

The equation of Discharge over a triangular notch

Q=8/15.Cd.√(2g).tan(Ѳ/2).H^(5/2)1 6

Discharge over a Trapezoidal notchA trapezoidal notch is a combination

of a rectangular notch and two triangular notches as shown in figure.

Hence discharge over a trapezoidal notch will be the sum of the discharge of rectangular notch and triangular notches.

Discharge over Trapezoidal notch= discharge over rectangular notch+

discharge over triangular notch Q= .Cd. L.⅔ √(2g).H^(3/2) + 8/15.Cd.

√(2g).tan( /2ᶿ ).H^(5/2)1 7

Weir A weir may be defined as a structure constructed across a river or canal

to store water on the upstream side. Water flows over the crest of weir.The top of a weir over which water flows is known as crest.A Weir is made of cement concrete or masonary.A weir is used to measure large discharge of rivers or big canals.

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Types of weirsa) According to the shape (a) Rectangular weir (b) Cippoletti weir b) According to the nature of discharge (a) Ordinary weir (b) submerged weir or drowned weirc) According to the width of crest (a) Narrow- crested weir (b) Broad-crested weird) According to the nature of crest (a) sharp crested weir (b) ogee weir 1 9

Cippoletti weir The Cippoletti weir is a trapezoidal

weir, having side slopes 1 horizontal to 4 vertical.

The purpose of slope, on the sides, is to obtain an increased discharge through the triangular portions of the weir, which otherwise would have been decreased due to end contractions in the case of rectangular weirs.

Fransis formula for Cippoletti weir is, Q=1.84 L . H^(3/2)General equation of discharge for

Cippoletti weir, Q= . Cd. L . ⅔ √(2g). H^(3/2)When velocity of approach is

considered, Q= .Cd.L. ⅔ √(2g).[H1^(3/2)-Ha^(3/2)1 10

Discharge over a Narrow-crested weirA narrow crested weir is

hydraulically similar to an ordinary weir or to a rectangular weir.

The equation of discharge over a narrow-crested weir

Q= .Cd. L . ⅔ √(2g). H^(3/2)

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Discharge over a Broad-crested weirThis is a weir having very broad

crest so that the flow of water over crest may be compared to the flow of water in a channel.

The equation of discharge over a Broad crested weir,

Q=Cd. L. h. √(2g(H-h))

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Discharge over a sharp-crested weir

It is a special type of weir, having a sharp crest. The water flowing over the crest comes in contact with the crest line and then springs up from the crest and falls as a trajectory as shown in figure.

The equation of Discharge over a sharp-crested weir

Q= . Cd. L . ⅔ √(2g). H^(3/2)

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Ogee weirWe know, in the case of a sharp

crested weir the nappe as it leaves the crest springs on rises slightly at the lower surface. In this way it reaches a maximum rise of 0.115 H above point ‘A’ and then falls. If the space below the bottom surface of the nappe be filled with masonary or concrete, the consequent weir formed is called ogee weir.

Is is generally used as a spillway of a dam.

The equation of Ogee weir Q= . Cd. L . ⅔ √(2g). H^(3/2)1 14

Submerged weir or Drowned weirA weir which the water level on the downstream

side of a weir is above the crest of the weir, is called Submerged weir or Drowned weir.

The total discharge over the weir is obtained by dividing the weir into two parts.

The portion of water between u/s and d/s water surface may be treated as free weir and portion between d/s water surface and crest of weir as a drowned weir.

Q1= discharge through upper portion Q= Cd. L. ⅔ √(2g).(H-h)^(3/2)Q2 = discharge through drowned portion =Cd2* area of flow * velocity of flow =Cd2* (L*h) * √(2g(H-h))Total discharge Q=Q1+Q2 = Cd. L. ⅔ √(2g).(H-h)^(3/2)+ Cd2* (L*h) *

√(2g(H-h))1 15

Difference between Notch & WeirNOTCHA notch may be defined as an opening provided in one side of a tank or reservoir, with u/s liquid level below the top edge of the opening.The bottom edge of notch over which water flows is known as sill or crest.A notch is usually made of a metallic plate.A notch is used to measure small discharge of small stream or canal.Notches are of small size.

WIERA weir may be defined as a structure constructed across a river or canal to store water on the upstream side.The top of the weir over which water flows is known as crest.A weir is made of cement concrete or masonary.A weir is used to measure large discharge of rivers and large canals.Weirsd are of bigger size.

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THANK YOU

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