City College of New York
School of Engineering
Department of Civil Engineering
CE 36500 –Hydrology and Hydraulic Engineering
Laboratory Experiment No. 1
Estimating the Friction Factor in a Brass Pipe
The system consists of a horizontal brass pipe, a pump, two differential
manometers and a small container, which is positioned on a scale. Transmission Oil
(s.g.=0.86) is pumped through the pipe; the end of the pipe is open to the atmosphere and
the transmission oil pours into the container. The oil is drained back from the container
into the system.
1. The friction factor will be estimated for five different volumetric flow rates.
2. The time to collect 14 lb of the oil is measured twice at each flow rate.
3. The average time of the two readings will be used to estimate the flow rate.
4. The corresponding volume of the oil is found by dividing 14 lb by the specific
weight of the oil.
5. Volumetric flow rate is calculated by dividing the volume of oil (step 4) by the
average collection time (step 3).
6. The two manometers are read at each flow rate.
7. The manometer readings are in height of mercury; they must be transformed into
the height of the oil.
8. Two manometers are connected to two different parts of the pipe; they
correspond to two different pipe lengths.
9. Using the manometer readings and the corresponding pipe lengths estimate f
using the Darcy-Weisbach equation.
10. The two friction factors for the two different lengths should be close.
11. Take the average of the two friction factors; this average corresponds to the
volumetric flow rate, which was estimated previously.
12. Compare you findings with the information given in the textbook.
( = 0.328 stoke)
City College of New York
School of Engineering
Department of Civil Engineering
CE 361 - Hydraulics
Laboratory Experiment No. 2
Velocity Profile Measurements in a Closed Conduit Using LDV
(Laser Doppler Velocimetry)
The dual beam approach is the most common optical arrangement used for an
LDV system. Basic components of a complete LDV system include a Laser,
Beamsplitter, Focusing lens, Collecting lens, Photodetector, Signal processor and Data
Analysis system. To optimize a measurement, one must have particles following the
flow.
1. The velocity profile is measured at the entrance, before the obstacle, after the
obstacle and at the exit.
2. Assuming symmetry, half of the profile is measured; the other half of the
profile is the mirror image of the measured part.
3. Set up your own coordinate system; you have to be able to specify the position
of the profile within the closed conduit.
4. The entire profile must be drawn at each section.
5. Interpret the shape of each profile and compare it to the situation with no
obstacle in the conduit.
6. The profiles at different sections must be compared as well; for example the
maximums and the minimums of the profile before the obstacle and the profile
after the obstacle should be compared.
City College of New York
School of Engineering
Department of Civil Engineering
CE 361 - Hydraulics
Laboratory Experiment No. 3 - Hydraulic Jump
Introduction
Hydraulic jumps mostly occur naturally in open channels. They are very efficient
in dissipating the energy of the flow to make it more controllable and less erosive. In a
hydraulic jump the flow goes from supercritical ( high velocity) to subcritical (low
velocity) regime. In fact, occasionally it might be necessary to create a jump to consume
the excessive energy. For instance when water flows down from an outlet of an arch dam,
it carries an enormous amount of kinetic energy, which might damage the receiving
channels. To avoid damage, a hydraulic structure called stilling basin is built underneath
the dam. This structure produces a controlled hydraulic jump, where the damaging energy
is lost in the transition from supercritical to subcritical.
Experimental Procedure
A hydraulic jump has been established in the elevated flume of the Hydraulics
Laboratory. The following tasks must be accomplished in this experiment:
1. Measure the width of the channel;
2. Measure the sequent depths of the jump;
3. Measure the flow depth upstream from the jump (subcritical region);
4. Estimate the flow velocity in the subcritical region of the flow;
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Choose two points in the channel in the subcritical region downstream
from the jump and measure their distance;
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Put a piece of paper on the flow surface and measure the time it takes
for the paper to travel from one point to the other. Repeat this
procedure three times and take the average travel time;
-
Divide the distance by the average travel time to approximate the flow
velocity at the water surface;
Report Preparation
1. Compute the average velocity using the equation provided in the laboratory;
2. Multiply the velocity by the cross sectional area (flow depth measured in step
3 in experimental procedure times width of the channel) to estimate the flow
rate.
3. Estimate the critical depth in the channel;
4. Estimate the Froude number before and after the jump;
5. Using the initial depth, approximate the sequent depth of the jump with the
appropriate relations given in your text book and compare it with your
measurement;
6. Repeat step 5 but use sequent depth to obtain the initial depth;
7. Estimate the energy loss in the jump;
8. Draw the specific force curve and specific energy curve;
9. Specify the sequent depths on each curve and answer the following questions:
(a) Are the specific forces of the initial depth and the sequent
depth exactly the same? Why?
(b) Is the energy loss that you obtain from the specific energy
curve the same as the one in step 9? Why?
City College of New York
School of Engineering
Department of Civil Engineering
CE 361 - Hydraulics
Laboratory Experiment No. 3 – Calibration of Sharp-Crested Weirs
Introduction
A weir is an overflow structure extending across a stream or a channel and normal to the
direction of the flow. They are normally categorized by their shape as either sharp-crested
or broad-crested. This laboratory experiment focuses on sharp-crested weirs only. Two
different types of weirs will be introduced:
1- The V-notch weir;
2- The rectangular weir (horizontal weir with end contractions).
Objectives
Estimation of coefficient of discharge for a rectangular and a V-notch weir.
Experimental Apparatus
The experiments will be carried out on a mobile "hydraulic bench" located in the
hydraulic laboratory. A schematic of the hydraulic bench is shown in Fig. 1. It consists
of five basic elements:
1- Flow channel, located at the top of the bench;
2- Water storage tank;
3- Pump/valve system, next to water storage tank;
4- Holding tank for water volume measurement, below the flow channel;
5- The drainage system for hydraulic bench.
Quick release connector is unscrewed from the bed of the channel and the delivery
nozzle (5) screwed in place. Stilling baffle (6) is slid into the slots in the walls of the
channel. These slots are polarized to ensure correct orientation of the baffle. The inlet
nozzle and stilling baffle in combination promote smooth flow conditions in the channel.
Water is circulated in the system by a small centrifugal pump between the channel and
the holding tank. A vernier hook and point gauge is mounted on an instrument carrier
(11), which is located on the side channels of the molded top. The carrier may be moved
along the channels to the required measurement position. The gauge is provided with a
coarse adjustment locking screw (7) and a fine adjustment nut (8). The vernier (10) is
locked to the mast by a screw (4) and is used in conjunction with the scale (9). The hook
and point (1) is clamped at the base of the vertical mast (3) by a thumb screw (2).
The rectangular weir or V-notch weir, which is to be calibrated (12), is clamped to the
weir carrier by thumb nuts (13). The weir plates incorporate captive studs to aid
assembly.
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8
9
10
11
6
12
5
13
4
3
2
1
Figure 1 . The Flow Channel
Experimental Procedure
1- Measure the width of the weir.
2- Turn on the pump and open the control valve until water discharges over the weir
plate.
3- Close the control valve and Turn off the pump and allow water level to drops until
water flow over the weir stops.
4- Set Vernier Height Gauge to datum reading (water surface in the channel).
5- Position the gauge at about half way between the plate and the stilling baffle.
6- Turn on the pump and open the control valve and adjust it to obtain the head H.
7- For each flow rate, after the conditions are stable, measure and record H.
8- Take readings of volume discharged and time of discharge using the volumetric
tank to determine the flow rate.
9- Repeat steps 5 to 7 five times for each weir type.
Data Analysis
A- Rectangular Weir
In a rectangular weir:
Q = 2/3* Cd * B*(2g)1/2* H1.5
where
Q = flow rate,
Cd = coefficient of discharge,
B = width of the weir, and
H = head above the weir.
Determine Cd as follow:
1- Tabulate volume, times, and heads;
2- Compute and tabulate Q, H2/3 , Cd=3Q/ (2BH1.5(2g)0.5), log Q, log H;
3- Plot Q2/3 versus H;
4- Plot log Q versus log H;
5- Plot Cd versus H;
6- Estimate an average value for Cd and the standard deviation.
Answer the following questions:
1- Is Cd constant for this weir?
2- Can The Q-H relationship be described by an empirical formula Q = k * Hn? If so
find the values of k and n.
B- V-notch Weir
In V-notch weirs:
Q = 8/15* Cd * (2g)1/2* tan (/2)*H5/2
where
Cd = coefficient of discharge,
/2 = half of the enclosed angle of the V, and
H = head above the weir.
Determine C in accordance with the following:
1- Tabulate volumes, times and heads;
2- Compute and tabulate Q and Q5/2 ;
3- Plot Q5/2 versus H and find Cd from the slope of the graph.
Answer the following questions:
1- Is Cd constant for this weir?
2- What are the advantages and disadvantages of plotting Q2/5 versus H instead of Q
versus H5/2 ?