IMPACT OF A JET

FACULTY OF CIVIL & ENVIRONMENTAL ENGINEERINGDEPT. OF WATER RESOURCES & ENVIRONMENTAL ENG.

FLUID MECHANICS ENGINEERING LABORATORY

REPORT

SUBJECT CODE BFC 10601

TEST CODE & TITLE MMB 01 / IMPACT OF A JET

COURSE CODE

TESTING DATE

STUDENT NAME

GROUP

GROUP MEMBER NAMES

1.

2.

3.

4.

5.

6.

LECTURER/INSTRUCTOR/TUTOR NAME

REPORT RECEIVED DATE

MARKS* Please refer laboratory rubric attached

EXAMINER COMMENT RECEIVED STAMP

1.0 OBJECTIVE

To Verify Theories Of Forces Generated By Impact Of The Jet On Different Shapes Of Vane

2.0 INTRODUCTION

Water turbines are widely used throughout the world to generate power. In the type of water turbine

referred to as a Pelton wheel, one or more water jets are directed tangentially on to vanes or buckets

that are fastened to the rim of the turbine disc. The impact of the water on the vanes generates a torque

on the wheel, causing it to rotate and to develop power. Although the concept is essentially simple, such

turbines can generate considerable output at high efficiency. Powers in excess of 100 MW, and

hydraulic efficiencies greater than 95%, are not uncommon. It may be noted that the Pelton wheel is

best suited to conditions where the available head of water is great, and the flow rate is

comparatively small. For example, with a head of 100 m and a flow rate of 1 m3/s, a Pelton wheel

running at some 250 rev/min could be used to develop about 900 kW. The same water power would

be available if the head were only 10 m and the flow were 10m3/s, but a different type of turbine would

then be needed. To predict the output of a Pelton wheel, and to determine its optimum rotational speed,

we need to understand how the deflection of the jet generates a force on the buckets, and how the force

is related to the rate of momentum flow in the jet. In this experiment, we measure the force generated

by a jet of water striking a flat plate or a hemispherical cup, and compare the results with the computed

momentum flow rate in the jet.

3.0 THEORY OF THE EXPERIMENT

A jet of water is produced when water is fed to a vertical pipe terminating in a tapered nozzle. The

jet will impinge on a vane, of different shapes. Vanes usually used are flat plate, inclined plate, curved

plate and hemispherical cup. Equation used to determine the force of jet impact (Fy) is given as:

Fy = Q ( Vy1 - Vy2 cos ) , Vy1 = initial velocity, Vy2 = final velocity (after impingement)

where,

1. Flat plate

Figure 3.1: Flat plate

2. 120 curved plate

Figure 3.2: 120o curved plate

where, from analysis, velocity after impingement

3. Hemispherical cup

where, velocity after impingement

Figure 3.3: Hemispherical cup

4.0 EQUIPMENTS

1. Hydraulic bench

2. Jet impact apparatus

3. Stop watch

4. Vernier caliper

Given:

Diameter of nozzle = 10 mm

Gravity acceleration, g = 9.81 ms– 2

From analysis, slope of the graph as in theory is given by:

Flat plate =

120 curved plate =

Hemispherical cup =

Figure 4.1: Equipments used 4.2: Jet impact apparatus

Figure 4.3: Jet Impact Apparatus

5.0 PROCEDURES

1. Firstly, the top plate and the transparent cylinder were took off. Then, the diameter of the

nozzle was measured. The flat plate assembled to the lever that carries a jockey weight.

2. The top plate and cylinder were assembled to the apparatus. The supply pipe was connected

from the hydraulic bench to the inlet pipe of the apparatus.

Figure 5.1: Arrangement of apparatus

3. The apparatus was first levelled and the lever was set to a balanced position (as indicated by

a tally supported from it) by placing the jockey weight at its zero position, and then the knurled nut

was adjusted above the spring.

Figure 5.2: Jockey weight restrained by a light spring

4. Any force generated by impact of the jet on the vane was measured by moving the jockey

weight along the lever until the tally shows that it had restored to its original balanced position.

5. Nominal weight was placed on the lever first (it is suggested that initial weight and

incremental weight = 20g). Water was then admitted through the bench supply valve.

6. The force on the vane would displaced the lever, which was then restored to its balanced

position by sliding the jockey weight along the lever. Then, the opening at the base of the hydraulic

bench was covered.

Figure 5.3: Move the jockey weight along the lever

7. The volume of water and time to determine the flow rate were recorded. The weight on the

lever was recorded too.

Figure 5.4: Determining flow rate

8. The procedure (step 1 to 7) for 120o curved plate and hemispherical cup were repeated.

6.0 RESULT AND CALCULATIONS

1. Record the readings in the table below.

a) Flat plate

Mass of jockey

weight m (g)

Volume of

water V (l)Time t (s)

Flow rate Q

(l/s)Q2

20 5 29.55 0.17 0.0289

40 5 20.79 0.24 0.0576

60 5 20.07 0.25 0.0625

80 5 18.14 0.27 0.0729

b) 120 0 curved plate

Mass of jockey

weight m (g)

Volume of

water V (l)Time t (s)

Flow rate Q

(l/s)Q2

20 5 38.30 0.13 0.0169

40 5 26.45 0.19 0.0361

60 5 19.90 0.25 0.0625

80 5 17.97 0.27 0.0729

c) Hemispherical cup

Mass of jockey

weight m (g)

Volume of

water V (l)Time t (s)

Flow rate Q

(l/s)Q2

20 5 45.46 0.11 0.0121

40 5 29.29 0.17 0.0289

60 5 26.14 0.19 0.0361

80 5 21.22 0.24 0.0576

2. Plot the graph of mass of jockey weight m versus Q2 for flat plate, 120o inclined plate and hemispherical

cup and find the slope of the graphs.

7.0 QUESTIONS

1. For every plate, record and calculate Q and Q2 and plot graphs of mass of jockey weight m versus

Q2. Theoretically, slope of the graphs is given as:

a. Flat plate

b. 120o inclined plate

c. Hemispherical cup

2. Compare the value between the slope at the graph and the theory value

a. Flat plate

b. 120o inclined plate

c. Hemispherical cup

3. From the result, comment on the graphs slope and theoretical value.

Answer:

1. a. Flat plate

b. 120o inclined plate

c. Hemispherical cup

2. a. Flat plate

The value for mass of jockey weight per Q2 for the flat plate is 6.8x105kgms-2

b. 120o inclined plate

The value for mass of jockey weight per Q2 for the 120o inclined plate is 899.54kgms-2

c. Hemispherical cup

The value for mass of jockey weight per Q2 for the hemispherical cup is 0.8023kgms-2

3. The value obtained from the graph and theoretical value is different. Where the value of slope from the graph is smaller compared to theoretical calculation.

8.0 DISCUSSION

Based on the result above, when the mass of jockey weight increase, the value of Q2 is increase, for

flat plate, 1200 curved plate and hemispherical cup.

The difference between the theoretical value and the actual value may mainly due to human and

servicing factors such as parallax error. This error occur during observer captured the value of the water

level. Besides that, error may occur during adjusting the level gauge to point at the white line on the side of

the weight pan. Other than that, it also maybe because of the water valve. This error may occur because the

water valve was not completely close during collecting the water. This may affect the time taken for the

water to be collected. There are a lot of possibilities for the experiment will having an error. Therefore, the

recommendation to overcome the error is ensure that the position of the observer’s eye must be 90°

perpendicular to the reading or the position. Then, ensure that the apparatus functioning perfectly in order

to get an accurate result.

9.0 CONCLUSION

As a conclusion, the experiment that have been carried out were successful, even though the data

collected are a little bit difference compared to the theoretical value.

10.0 REFERENCE

1.http://www.cee.mtu.edu/~dwatkins/ce3600_labs/impact_of_jet.pdf 

2. http://www.eng.ucy.ac.cy/EFM/Manual/HM%2015008/HM15008E-ln.pdf 

3.http://staff.fit.ac.cy/eng.fm/classes/amee202/Fluids%20Lab%20Impact%20of%20a%20Jet.pdf 

4. Roberson, J.A. and Crowe, C.T,1993. Engineering Fluid Mechanics, Published by Houghton Mifflin

Harcourt, Boston, MA.

11.0 APPENDIX