unimasr.com ed5e80166f74fd917dee7a5e9cc66163

7/26/2019 UniMasr.com Ed5e80166f74fd917dee7a5e9cc66163

1/19

Cairo University Fluid MechanicsFaculty of Engineering 2ndYear Civil Engineering

Irrigation and Hydraulics Department 2010 - 2011

1

Fluid Mechanics

Laboratory Manual

Irrigation and Hydraulics Department

2010 2011


2/19



2

Table of Contents

Description of the Hydraulic Bench 3

1. Weir Experiment (Rectangular and Triangular)... 5

2. Impact of Jet .... .9

3. Flow through Sharp Edged Orifice .13

4. Bernoullis Theorem Demonstration ..18


3/19



3

The Hydraulics Bench

The standard Hydraulics Bench is used for all the laboratory experiments carried out during this

course. The Bench has a closed water circulating system to facilitate mobility. Water is stored in an

enclosed tank at the bottom of the bench then pumped up to the experimental setup situated on top of

the bench from which water flows into the upper tank. The upper tank has a drain controlled by a plug

to collect and gauge the water in the upper tank after which water is drained to the bottom tank. The

volume of water collected in the upper tank (in liters) can be measured using the graduated scale fixed

at the side of the Hydraulics Bench. The switch of the water pump and the control valve that regulates

the amount of water that flows to the experimental setup are at the front side of the Hydraulics Bench

(Please see the attached photographs).

Scale of

the volume

(liter)

ControlValve

Pump

Switch

Upper tank of

the bench

Plug and sinkto drain water

to the lower


4/19



4

Scale of

the volume

(liter)

Control

Valve

Pump

Switch

Upper

tank of the

bench

Plug and sink todrain water to the

lower tank


5/19



5

1.Weir Experiment (Rectangular and Triangular)

Objectives of the Experiment

1. To demonstrate the flow over different weir types.

2. To calculate the coefficient of discharge for different weir types.

3. To study the variation and dependence of the relevant parameters.

Theory

For the rectangular weir:

2

3

d H.g2.B.3

2.CQ =

For the triangular weir:

2

5

.2.2

tan.15

8. HgCQ d

=

where Cd = Coefficient of discharge

B = width of the rectangular weir (3 cm)

H = head above the weir crest or apex

= angle of the triangular weirg = acceleration of gravity

Experimental Setup

Weir Plate

(V-notch)

Stilling

Baffle

Point

Gauge

OpenChannel


6/19



6

1. The rectangular or triangular weir plate is attached to the regular Hydraulic Bench as shown

in the photographs.

2. A stopwatch, a hook or a point gauge are also needed with the experiment.

Procedures and Readings

1. Make sure that the Hydraulic Bench is leveled.

2. Set the Vernier on the point gauge to a datum reading by placing the tip of the gauge on the

crest or the apex of the weir. Take enough care not damage the weir plate and the point

gauge.

3. Put the point gauge half way between the stilling baffle plate and the weir plate.4. Allow water to flow into the experimental setup and adjust the minimum flow rate by

means of the control valve to have atmospheric pressure all around water flowing over the

weir. Increase the flow rate incrementally such that the head above the weir crest increases

around 1 cm for each flow rate increment

5. For each flow rate, wait until steady condition is attained then measure and record the head

(H) above the weir.

6. For each flow rate, measure and record the initial and final volumes in the collecting tank

and the time required to collect that volume. For each flow rate, take 3 different readings of

the volumes and time and record the averages.

Calculations and Results Interpretation

A. Rectangular weir:

Fill the following table of observations

Reading Crest level

(C.L.) (mm)

Water level

(W.L.)(mm)

Initial volume

(I.V.) (liter)

Final volume

(F.V.) (liter)

Time (T)

(sec)1

2

3

4

5


7/19



7

Fill the following table of results

Reading Volume = F.V.-I.V.(liter)

H = C.L.-

W.L.(cm)Time

(sec)

Q= volume/time(cm3/s)

Log Q Log H H1.5

Cd

1

2

3

4

5

Plot Q against H, Q against H1.5

, log Q against log H, Cdagainst H, and obtain the Cdfrom the slopesof the two linear graphs. Compare the three obtained values of the Cd

B. Triangular weir:

Fill the following table of observations

Reading Crest level

(C.L.) (mm)

Water level

(W.L.)(mm)

Initial volume

(I.V.) (liter)

Final volume

(F.V.) (liter)

Time (T)

(sec)

1

23

4

5


Reading Volume = F.V.-I.V.(liter)

H = C.L.-

W.L.(cm)Time

(sec)

Q= volume/time(cm3/s)

Log Q Log H H2.5

Cd

1

23

4

5

Plot Q against H, Q against H5/2

, Log Q against Log H, Cdagainst H, and obtain the Cdfrom the slopesof the two linear graphs. Compare the three obtained values of the Cd


8/19



8

Suggestions for Conclusions and Comments

1. Is Cdconstant? Give comments.2. Can the Q-H relation be described by an empirical formula? If so, assume the relation

is in the form of nkHQ = and find the constants k and n.

Example (V-notch experiment)

H = C.L. - W.L.

(cm)

volume

(lit)

time

(sec.)

Q

(cm3/s) H2.5 Q2/52 5 76 65.79 5.66 5.34

2.3 5 53 94.34 8.02 6.16

2.5 5 41 121.95 9.88 6.83

2.8 5 32 156.25 13.12 7.54

slope = 11.974

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

160.00

180.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00

H^2.5

Q

Cd = slope*15/(8* g2.2

tan

) = 0.507


9/19



9

2. Impact of Jet

Objective of the Experiment

To demonstrate and investigate the validity of theoretical expressions for the calculation of theforce exerted by a jet on objects of various shapes.

Theory

From momentum principle,

)cos.vv(QFy = where AQ

v =

For flat plate (90),A

QF

2

y =

For 120 plate,A2

Q3F

2

y =

For hemispherical target 180,A

Q2F

2

y =

90o

FLAT PLATE HEMISPHERE 120 DEG CONE

Experimental Setup

1. The impact of jet apparatus is placed above the regular Hydraulic Bench as shown in the

photographs.

2. A stopwatcher.


10/19



10


1. Remove the stop plate and transparent casing to measure the nozzle diameter and place the

flat plate (90) on the rod attached to the weight pan. Then, reassemble the apparatus.

2. Connect the inlet pipe of the apparatus to the outlet of the Hydraulic Bench.

3. Level the base of the apparatus using the bubble balance.

4. Screw down the top plate to datum on the spirit level.

5. Adjust the level gauge to suit datum on the weight pan.

6. Add masses to the weight pan. Allow water to flow in the experiment and adjust the flow

by the control valve of the Hydraulic Bench so that the pan will be re-adjacent to the level

gauge.

7. Before taking readings the weight pan should be oscillated upwards and downwards and

rotated to minimize the effect of friction.

8. Take the readings of the initial and final volumes and the time of accumulation.

9. Record the masses on the weight pan.

10.Repeat the experiment for different masses on the weight pan.

Nozzle

Plates with

different shapes

Target Plate

Pointer

(spirit level)

Weight pan

From

PumpGlass

housing

Weights

Water

bubble

level


11/19



11

11.Repeat the previous steps with different shapes of plates (120 and the hemispherical

target).


For each plate, fill the following table of observations

Reading Mass on weight

pan

M (gm)

Initial volume

(I.V.) (liter)

Final volume

(F.V.) (liter)

Time (T)

(sec)

1

23

4

5


Reading Mass on weight

panM (gm)

Volume =

F.V.-I.V.(liter)

Time

(sec)

Q= volume/time

(cm3/s)

Q2

1

2

3

4

5

Plot mass M on weight pan with Q2

From the analysis, verify that the slope of the graphs should be:

Flat plate =gA

120 plate =gA

5.1

Hemispherical target =gA

2

Calculate the Coefficient of Impact = (Fact / Fcalculated)

Nozzle Diameter = 8 mm

g = 9.81 m/s2


12/19



12

Suggestions for Conclusions and Comments

1. Comment on the coefficient of impact.

2. Comment on the results of the computed slope and the shape of the target plate.

Example (flat plate)

m (gm) V (lit) T (sec)Q(cm3/s) Q

2

280 5 13 384.6154 147929

230 5 14 357.1429 127551

180 5 16 312.5 97656.25

130 5 20 250 62500

solpe = 0.0019

0

50

100

150

200

250

300

0 20000 40000 60000 80000 100000 120000 140000 160000

Q^2

m

gA

=0.0202

slope = 0.0019


13/19



13

3. Flow through Sharp Edged Orifice.


1. To study the path of water jets issuing from orifices.

2. To determine the coefficients of discharge, velocity and contraction from a sharp-edged

circular orifice.

3. To study the variation and dependence of the relevant parameters.

Theory

The coefficient of discharge Cdis the ratio of the actual discharge Qactto the theoretical discharge Qth.

The theoretical discharge is given by the following relationship where A is the area of the orifice and H

is the total head on the orifice centerline and the actual discharge can be measured.

gH2AQ th= & 0.1Q

QC

th

a

d


14/19



14

Experimental Setup

The regular Hydraulic Bench is used in this experiment

1. The orifice plate apparatus is placed above the regular Hydraulic Bench as shown in the

photographs.

2. A stopwatch is needed.

3. The adjustable stainless steel overflow pipe near the top of the tank is used to adjust the

level of water in the tank.

Orifice

Pointers

(thin pins)

Constant

head tank

Metal piece

for over flow

ScalePaper


15/19



15


16/19



16


1. Turn on the pump of the hydraulic bench and allow water into the constant head tank tobuild up above the orifice. Wait until steady condition is achieved.

2. You can control the level of the water into the constant head tank by pulling up and down

the adjustable stainless steel overflow pipe as shown in the photograph.

3. Measure the head (H) above the orifice using the graduated scale.

4. By setting the thin pins so that they just touch the issuing water jet, draw the path of the

water jet on the given graph paper.

5. Measure and record the initial and final volumes and the time of accumulation for each

reading of head (H).

6. Repeat the previous steps for at least four more different heads (H) by changing the position

of the adjustable stainless steel overflow pipe.


For each reading of head (H), fill the following table of observations

Point(1) Point(2) Point(3) Point(4) Point(5) Point(6) H (cm)

Initial

volume

(liter)

Final

volume

(liter)

X(cm)

Y(cm)

1. Calculate the theoretical flow rate using the measured head and the area of the orifice.

2. Calculate the actual flow using the volume and time recorded.

3. Calculate the coefficient of discharge Cd.

4. draw x2-y relationship and determine the coefficient of velocity

5. Repeat the above mentioned steps for various values of measured head

6. Plot Qaagainst (H)0.5

7. Comment on the graphs and on the slope of each graph.

8. Is the coefficients of the orifice is constant with change of water head


17/19



17

Example

point1

point2

point3

point4

point5

point6

H(mm) V (lit) T (sec)

X (cm) 5 10 15 20 25 30

Y (cm) 0.2 0.7 1.5 1.8 4.2 5.7

X2 25 100 225 400 625 900

Cv = (X2/4YH)

0.5 0.88 0.94 0.97 1.18 0.96 0.99

400 7 150

Dorifice= 6mm

vth= (2gH)0.5 =

280.14 cm/sec

Qact= V/T = 46.67 cm3/s

Qth= aorifice* vth= 79.17 cm3/s

Cd = Qact/Qth = 0.589

Cv = (X2/4YH)

0.5

SLOPE = 4HCv2 =

158.28

Cv = 0.995

Cc = Cd/Cv = 0.592

slope = 158.28

0

100

200

300

400

500

600

700

800

900

1000

0 1 2 3 4 5 6

Y

X^2


18/19



18

4. Bernoullis Theorem Demonstration


1. To demonstrate the variation of the pressure along a converging-diverging pipe section.

2. To verify the Bernoullis Theorem.

Theory

For ideal flow at any section on the pipe,

++ Z

g

p

g

v

2

2

= constant.

In the experimental setup, the pipe is horizontal (i.e. Z = constant). Therefore along the pipe,

g

p

g

v

+

2

2= constant

Experimental Setup

The Bernoullis experimental setup is placed on the top of the regular Hydraulic Bench.

Control

Valve

Glass

Venturimeter

Water

Manometer

From the

Pum

To the

Venturi

Airinlet

Pitot

TubeAir

bubble


19/19



19

Procedures

1. Level the Bernoullis experimental apparatus on the Hydraulic Bench by adjusting the

screw legs.

2. Switch on the pump and open the flow control valve to fill the entire apparatus and

manometers with water. Ensure that no air is entrapped in the apparatus or any of the

manometers by opening the air valve at the right end of the air chamber connecting the top

ends of the manometers. Make sure to close the air valve again.

3. Adjust the flow rate into the experiment by the flow control value in the apparatus.

4. To make visible the water levels in the manometers, connect and work the hand air pump at

the air inlet (shown in the photograph) to raise the air pressure in the air chamber, thuspushing the manometer columns down into the glass tubes.

5. Carefully adjust both flow control valves in the apparatus and in the Hydraulic Bench to

provide the combination of flow rate and pressure within the pipe such that the pressure

difference between the highest and the lowest manometer levels is reasonable.

6. Observe the variation of the scale readings of the water levels in each manometer tube.

7. Push the stainless steel probe (pitot-tube) at the right end of the horizontal transparent

section of the pipe into the tapered portion of the pipe. Position its end at stations adjacent

to the manometer openings in the pipe one station at a time. For each position, observe the

corresponding scale reading of the manometer to the probe. Compare the pitot-tube reading

to the manometer reading connected to the same position.

8. Repeat the previous steps with different flow rates at high and low static pressure for

different combinations of valve opening.

unimasr.com ed5e80166f74fd917dee7a5e9cc66163

Documents