Fluid mechanics lab experiments Textbook: Laboratory Manual

Reference: Textbook and handouts for Introduction to Water Resources; Fundamentals of Fluid Mechanics 4th Edition (Munson, Young, and Okishi).

Instructor: Dr. H. Prashanth Reddy,

COURSE POLICY

Grading: Laboratory reports 30% Data Analyses Exercise 15% Lab participation and technique 15%

Exam 40%________

Total 100%90-100 A80-89 B70-79 C60-69 D<60 F

Important Note: Free discussion, inquiry, and expression are encouraged in any academic activity inside and outside of the classroom. Such actions should be conducted in a professional manner.

Course Objective

• To strengthen the student's understanding of the principles of hydraulics through observation and hands-on participation;

• To help the student to visualize different flow phenomena and the performance of various hydraulic devices;

• To familiarize the student with methods for flow measurement.

Why we conduct experiments?

• To understand physical processes in controlled environment

• To provide data for model validation

What we need to be aware of?

Before conducting an experiment one must ask the question ‘WHY’

If the objective is to develop a relationship then how universal that relationship is going to be?

What are the most important parameters?

Topics

Laboratory Experiments:

– Major losses in pipe flow (Exp 1)

– Sharp-crested weirs (Exp 2)

– Wave speed (Exp 3)

– Pumps in series (Exp 4)

– Hydraulic jump (Exp 5)

– Pumps in parallel (Exp 6)

– Water surface profile-1 (Exp 7)

– Water surface profile-2 (Exp 8)

Laboratory Experiment 1: Pipe friction

Objective

The objective of this experiment is to determine the

variation in friction factor with flow rates.

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Experiment 1

Expt 1 Manometer readings

Objective The objective of this experiment is to calibrate sharp crested weir as a flow measuring device.

Objective The objective of this experiment is to demonstrate and measure the wave speed in a stationary fluid and compare the measured wave speed with its theoretical value.

Experiment 4: Pumps in series

ObjectiveThe objective of this experiment is to determine the head-capacity curve for a centrifugal pump, and for two centrifugal pumps operating in series.

Hydraulic Jumps are used to

• dissipate excessive energy of water flowing over spillways, weirs and other hydraulic structures and thus prevent scouring downstream of the structures;

• recover head or raise the water level on the downstream side of a measuring flume and thus maintain high water level in the channel for irrigation or other water distribution purposes;

• increase weight on an apron and thus reduce the effect of uplift pressure under a masonry structure by raising the water depth on the apron;

• mix chemicals used for water purification; • aerate water for city water supplies.

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Specific Energy Equation

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Normalized Specific Energy diagram

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PROCEDUREPROCEDURE

1. The flume should be in a horizontal position. Measure the opening of the sluice gate.

2. Start the pump.3. Wait until the jump is stationary in the flume. You may want to

adjust the downstream gate to ensure that the jump becomes stable in the mid-section of the flume.

4. Measure y1 and y2. Measure these values at least at three points across the channel. Be very careful in measuring these values. A small error in measurement can cause serious problem when you analyze the data.

5. Measure the discharge by volume using a bucket and stop-watch.6. Repeat steps 3 to 7 for at least 5 different discharges.7. Close the valve and turn the pump off.

PUMPS IN PARALLEL

when one pump is inadequate to deliver the necessary flow at a specified pressure, two or more pumps in parallel may be used. The effect of two pumps in parallel is that each pump delivers flow for the specified pressure, and these flows combine to increase the total amount of water being pumped, while maintaining nearly the specified pressure.

Performance curve of two pumps in parallel

Single Pumpi. Make sure that all valves are closed except valve 5. ii. Start pump A iii. Open valve 2 gradually to its maximum discharge.iv. Take the pressure gauge reading (shutoff head).v. Open valve 1 gradually until the gauge indicator drops two marks. Allow the flow to

stabilize.vi. Take the gauge reading and measure the flow rate by volume using a bucket and

stop-watch.vii. Repeat step 5 and 6 until the valve 1 is completely open giving maximum discharge.

You should take a total of 9~10 readings.viii. Close valve 2 at and turn the pump off.ix. Close valve 1.x. For pump B repeat steps from 1 to 9 using valve 3 instead of valve 2.Pumps in paralleli. Make sure that all valves are closed except valve 5. ii. Start up pumps A and B.iii. Open valve 2 and 3 gradually to maximum discharge.iv. Take the pressure gauge reading (shutoff head).v. Open valve 1 gradually until the gauge indicator drop two marks.vi. Take the gauge reading and measure the discharge by volume using a bucket and

stop-watch.vii. Repeat step 5 and 6 until valve 1 is completely open giving the maximum discharge. viii. Close valves 2 and 3, and turn the pumps off.ix. Close valve 1.

Exp-7 Uniform and Gradually varied Exp-7 Uniform and Gradually varied flowflow

ObjectivesThe objectives of this experiment are 1. to measure non-uniform flow depths during

subcritical flow conditions and 2. to estimate Manning’s roughness coefficient.

Gradually varied flow

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Bed level

Water surface

Normal depth

The Manning equation can be used to determine the normal flow depth

We will use measured quantity to determine the Manning roughness coefficient in a wooden flume

PROCEDURE

• Establish a datum and zero point in the x-direction. The zero point should be set near the downstream end of the flume. Measure slope and width of the wooden flume near the stair case.

• The pump will be on and the downstream gate level should be set at the normal depth level. Record the manometer reading and calculate the discharge from the relationship given on the chart. The manometer reading may fluctuate. Take an average value.

• Measure the water depth along the working section of the flume at least at 1 m, 1.5 m, 2 m, 2.5 m, 3 m, 3.5 m, and 4.0 m from the upstream end as marked by a tape measure installed on the top of the flume. Use a ruler to measure the water depth.

• Calculate Manning’s n from each of these measurements. Calculate the average value.

• Set the downstream gate level at a height of 20 cm. Allow the flow to become steady.

• Measure the water depth along the entire channel at 0.1 m interval for a distance of 2 m from the downstream and at an interval of 0.25 m for the rest of the flume.

• Plot your data on the gradually varied flow profile in the excel file provided with the lab module.

Exp 8. Uniform and Gradually varied Exp 8. Uniform and Gradually varied flowflow

The objective of this experiment is

To compute H-2 water surface profile validating with actual profile

H2 Profile

The Manning equation and standard step method can be used to compute the water surface profile

PROCEDURE• Establish a datum and zero point in the x-direction. The zero point should be set near the

downstream end of the flume. Make the flume horizontal

• Remove the downstream gate

• The pump will be on and the Allow the flow to become steady.

• Record the manometer reading and calculate the discharge from the relationship given on the chart. The manometer reading may fluctuate. Take an average value.

• Measure the water depth along the entire channel at 0.1 m interval for a distance of 2 m from the downstream and at an interval of 0.25 m for the rest of the flume.

• Plot your data on the gradually varied flow profile in the excel file provided with the lab module.

• Compute the critical depth for given flow and compute water surface profile by using standard step method use mannings value as determined in expt 7.

• Compare theoretical plot and actual plot