Civil 151 Fluid Mechanic Laboratory Experiment Manual 2
Fluid Flow measurement
1. Objective:
To observe characteristics of flow over a rectangular notch (part A) and a Vee notch
(part B)
2. Experimental setup:
A Hydraulic Bench, Hook and point Guage, Stop watch, Rectangular notch and Vee
notch
1
3.
Part A: Rectangular notch weir
3.1 Summary of Theory
By applying the Bernoulli Equation (conservation of energy equation) to a
simplified flow model of a rectangular notch weir, we can develop the following
relationship:
3
2
Q  Cd L 2 g H 2
3
1
Robert L. Street, Gary Z. Watters, John K. Vennard, Elementary Fluid Mechanics (1996, 7 th edition), P.668
Robert L. Street, Gary Z. Watters, John K. Vennard, Elementary Fluid Mechanics (1996, 7th edition), P.667
1
Robert L. Street, Gary Z. Watters, John K. Vennard, Elementary Fluid Mechanics (1996, 7 th edition), P.667
1
Where
Q = Discharge
Cd = Coefficient of discharge
L = Breath of notch
H = Head above bottom of notch
Note: The coefficient of discharge allows for the differences between the simplified
flow model used to derive the above formula and the real flow situation.
3.2 Procedure:
1) Insert the rectangular weir into the hydraulic bench and fit the weir tightly by using
screws in order to prevent leakage to occur.
2) Open the water supply and allow water flow over the weir. (i.e. H is not equal to
zero).
3) Adjust the water supply so as to make the water level become steady. Let the water
flow over the weir and wait until steady state of flow is reached.
4) Adjust the Vernier Height Gauge and its pointer just touch the water surface. Set
the reading to be zero so that the bottom of the notch is taken as the datum. Make
sure the vernier does not slide along the mast during the experiment until all data
have been recorded.
5) Open the water supplies again slowly, adjust the flow rate and measure the head (H)
by the vernier. Before measuring, wait at least one minute for letting the flow to
stabilize. Then measure the H for twice for better accuracy.
6) Switch on the stopwatch and record the time for admitting 10 litres of water
flowing over the weir. Also, measure the time for 10 litres of water flow. Find the
difference between the times. It is a good way to maintain the consistency of the
experiment. If the difference between the two ‘times’ is greater than one minute,
measure the time again as the error is too large.
7) Repeat step 4 to step 6 by using different flow rate of water, which can be done by
adjusting the water supply. Measure and record the H and the time for 10 litres to
flow until 10 sets of data have been taken.
8) Record breadth of notch for calculation of discharge coefficient.
3.3 Result and calculation
1. Please derive theory from 1st principle i.e. conservation of mass and energy.
2. Please calculate and plot relevant graphs to show your results.
3. You may suggest a functional relationship between discharge coefficient
and other parameters.
4. Discuss assumptions of the theory and possible experimental errors.
4.
Part B: Vee-notch Weir
4.1 Summary of theory
Similarly, by applying Bernoulli equation (conservation of energy equation) to a
simplified flow model of a Vee-notch, we can develop the following relationship:
8
 
Cd tan    2 g  H 2
15
2
5
Q
Where
Q = Discharge
Cd = Coefficient of discharge
/2 = Half the enclosed angle of the Vee
H = Head above bottom of notch
4.2 Procedure
Please follow same procedures described in part 3.2 except that a vee notch,
instead of a rectangular notch, should be installed to the hydraulic bench.
4.3 Result and calculation
1. Please derive theory from 1st principle i.e. conservation of mass and energy.
2. Please calculate and plot relevant graphs to show your results.
3. You may suggest a functional relationship between discharge coefficient
and other parameters.
4. Discuss assumptions of the theory and possible experimental errors.
5
Deadline for report submission
1. Each group of students MUST submit one report to pigeon hole outside TA
office (rm2126) 2 weeks after the date of experiment.
2. The report should be typed and well-written. Poor report will not be accepted.
3. Copying is not allowed and reference must be clearly stated at the end of report.
ZERO marks might be given if cases of plagiarism are found.
Data Logging sheet
Group no._________
Rectangular-notch Weir
H (mm)
Volume (L)
Time (s)
Trial 1
Trial 2
Trial 3
Trial 4
Trial 5
Trial 6
Trial 7
Trial 8
Trial 9
Trial 10
Vee-notch Weir
H (mm)
Volume (L)
Time (s)
Trial 1
Trial 2
Trial 3
Trial 4
Trial 5
Trial 6
Trial 7
Trial 8
Trial 9
Trial 10
Note: Please hand in this data sheet RIGHT AFTER the laboratory section.
Data Logging sheet
Group no._________
Rectangular-notch Weir
H (mm)
Volume (L)
Time (s)
Trial 1
Trial 2
Trial 3
Trial 4
Trial 5
Trial 6
Trial 7
Trial 8
Trial 9
Trial 10
Vee-notch Weir
H (mm)
Volume (L)
Time (s)
Trial 1
Trial 2
Trial 3
Trial 4
Trial 5
Trial 6
Trial 7
Trial 8
Trial 9
Trial 10
Note: Please hand in this data sheet RIGHT AFTER the laboratory section.