1 Department of Civil Engineering The University of Queensland Laboratory classes CIVL3140 Introduction to Catchment Hydraulics Laboratory work is closely linked with the lecture program and is an INTEGRAL part of the fluid mechanics/hydraulics course. It is intended to draw to the student's attention the behaviour of real fluid flows. Four laboratory classes are scheduled for each student, running from weeks 3-6 and week 8-11 of the semester. Laboratory classes will run on monday to thursday 9weeks 3-6 & 8-11 only) depending on students’ timetables. ATTENDANCE Each student is required to attend all laboratory sessions. Each student will sign up for a group of 12 people, with 3 groups of 4 students per experiment. Timetables will be posted on the noticeboard in the Fluid mechanics laboratory at the beginning of each semester. Attendance is COMPULSORY and any unavoidable absence must be made up at the next available opportunity after consultation with the laboratory coordinator. [Note however that groups larger than 5 will be forbidden for safety reasons. Students must organise swaps before the end of the laboratory class period.] SAFETY REGULATIONS Adequate shoes or boots must be worn in the laboratory. Sandals or open footwear are NOT permitted. Strong clothing is recommended, incl. shorts and trousers. (No skirt, dress nor loose clothing.) The attached safety form must be completed and submitted to the TUTOR at the start of the FIRST lab session. ASSESSMENT The Laboratory assessment includes a combination of {a} Attendance, {b} Pre-Lab calculations, {c} Individual work during the afternoon, and {d} Group report. No individual reports are required to be submitted for this subject. The marks for the laboratory work and pre-lab calculations will be worth the Laboratory class component of the course. [1] Pre-requisite calculations : each student is required to perform INDIVIDUALLY the pre-lab calculations and submit them to the relevant tutor prior to the start of the experiment. (It will be assessed and later included in the group report.) [2] Pre-formatted report : each student group will complete one report during the experiment and it will be submitted for marking at the conclusion of the experiment. During the afternoon, there is a strong emphasis on group work. Each group (3-4 students) will complete a pre-formatted report during the experiment and submit it for marking at the conclusion of the experiment. The pre-formatted laboratory reports must be prepared to the format specified below and credit is given for them in accordance with the credit points of the subject. The final examination may have some question based on the experiments. Failure to satisfy in laboratory work will result in the failure in the subject : i.e. students who did not attend an experiment or who fail to complete a satisfactory laboratory report shall fail the subject. It is the responsibility of each and every student who miss a prac to organise swaps before the end of the laboratory class period (i.e. before end of teaching class period). [Practicals will run from weeks 3-6 and 8-
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Department of Civil Engineering The University of Queensland
Laboratory classes CIVL3140 Introduction to Catchment Hydraulics
Laboratory work is closely linked with the lecture program and is an INTEGRAL part of the fluid mechanics/hydraulics course. It is intended to draw to the student's attention the behaviour of real fluid flows. Four laboratory classes are scheduled for each student, running from weeks 3-6 and week 8-11 of the semester. Laboratory classes will run on monday to thursday 9weeks 3-6 & 8-11 only) depending on students’ timetables. ATTENDANCE Each student is required to attend all laboratory sessions. Each student will sign up for a group of 12 people, with 3 groups of 4 students per experiment. Timetables will be posted on the noticeboard in the Fluid mechanics laboratory at the beginning of each semester. Attendance is COMPULSORY and any unavoidable absence must be made up at the next available opportunity after consultation with the laboratory coordinator. [Note however that groups larger than 5 will be forbidden for safety reasons. Students must organise swaps before the end of the laboratory class period.] SAFETY REGULATIONS Adequate shoes or boots must be worn in the laboratory. Sandals or open footwear are NOT permitted. Strong clothing is recommended, incl. shorts and trousers. (No skirt, dress nor loose clothing.) The attached safety form must be completed and submitted to the TUTOR at the start of the FIRST lab session. ASSESSMENT The Laboratory assessment includes a combination of {a} Attendance, {b} Pre-Lab calculations, {c} Individual work during the afternoon, and {d} Group report. No individual reports are required to be submitted for this subject. The marks for the laboratory work and pre-lab calculations will be worth the Laboratory class component of the course. [1] Pre-requisite calculations : each student is required to perform INDIVIDUALLY the pre-lab calculations and submit them to the relevant tutor prior to the start of the experiment. (It will be assessed and later included in the group report.) [2] Pre-formatted report : each student group will complete one report during the experiment and it will be submitted for marking at the conclusion of the experiment. During the afternoon, there is a strong emphasis on group work. Each group (3-4 students) will complete a pre-formatted report during the experiment and submit it for marking at the conclusion of the experiment. The pre-formatted laboratory reports must be prepared to the format specified below and credit is given for them in accordance with the credit points of the subject. The final examination may have some question based on the experiments. Failure to satisfy in laboratory work will result in the failure in the subject : i.e. students who did not attend an experiment or who fail to complete a satisfactory laboratory report shall fail the subject. It is the responsibility of each and every student who miss a prac to organise swaps before the end of the laboratory class period (i.e. before end of teaching class period). [Practicals will run from weeks 3-6 and 8-
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11, with a break in week 7. No special Prac session shall be scheduled because of the large demand on the laboratory facilities and time-table classes with other activities. The first set of experiments may be dismantled at the end of week 6, while some major refurbishment works will take place in the laboratory from week 12. NO further laboratory session shall be organised.] PROCEDURE 1- At least 1 day before each scheduled lab session, each student is advised to visit the laboratory, inspect the apparatus, and prepare a preliminary sketch of it. Students are expected to read the information materials before commencing each experiment. It is important to start promptly at (or before) 2:00 pm since experimental work must usually be finished by 4 pm and laboratory classes must end no later than 4:50pm. (NOTE: the laboratory is open from 1:30 pm and students are strongly encouraged to start their experiment as early as possible; tutors are not needed to start the work). 2- During each afternoon, students perform one experiment during which experimental results are recorded on result sheets, white boards or computer spreadsheets and relevant graphs can also be plotted. Further analysis of experimental results and discussion with the supervisors are developed. At the end of the afternoon, students must have their work approved by the tutor before leaving. REPORTS At the beginning of each afternoon, each group will find a report form next to the experiment. The report is to be completed by the end of the afternoon. The students' names must be on the cover. The folder should be handed in for perusal and comment at the end of the laboratory session before 4:50pm. Comments A proper laboratory report requires a detailed description of the experimental work as well as of the calculations. Some points must be noted : - List of experimental data, e.g. atmospheric conditions, sizes of significant parts of the apparatus, etc. - Results. It is GOOD experimental practice to record and retain all data from an experiment. However, except when indicated in the instruction sheet, it will NOT be necessary to record tables of raw data, since the reduction of results to graphical presentation has been performed and agreed in the final hour of the laboratory session. Where possible students should ALWAYS compare their experimental results with those contained in the literature and should quote any references used. - Calculations. Sample calculations used in obtaining the required results from experimental data must be shown. - Discussions. Each instruction sheet includes some discussion questions; a satisfactory response to these questions is an essential requirement. SPECIAL NOTES REGARDING GRAPHS AND TABLES Graphs and tables are records of results, and these should be placed with the report. All graphs and tables must be prepared in such a manner that ALL titles, axis labels and scales, units and legends are easily legible.
Student Safety Declaration Form for Practical Class Work
This form must be completed by the Student and given to the Lecturer or Tutor during the first practical class. No experimental work should start until this form has been completed. Name: (Please Print) …………………………………………………………………….. Student Number: …………………………………………………………………….. Course Code: …………………………………………………………………….. YES NO • I have read and I understand the Occupational Health and Safety in the Laboratory guidelines (Undergraduate Student Edition)
• I am aware of my Workplace Health and Safety responsibilities
• The tutor has explained what personal protective equipment (PPE) is required for this course. I agree to wear it when required
• I understand that if I am not wearing appropriate PPE, I can be excluded from the laboratory for that class
• I agree to follow all safety procedures explained to me by the tutor
• I understand that I must not eat food or drink in the laboratory
• I understand that inappropriate conduct can result in the denial of further laboratory access
• I understand that all accidents, including ‘near miss’ incidents need to be reported to the lecturer or tutor immediately
• I understand that all faulty or broken equipment needs to be brought to the attention of my tutor immediately
• I am familiar with the emergency procedures for the laboratory and are familiar with the location of the eye wash and safety shower
• I understand the procedures outlined in this guideline regarding pregnancy Student Signature: ………...…………………………………………………………...
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CIVL3140
Department of Civil Engineering - The University of Queensland
Laboratory classes : CIVL3140 Introduction to Catchment Hydraulics Four practical studies are planned as part of the subject CIVL3140 Introduction to Catchment Hydraulics. These laboratory experiments are closely linked with the lecture program and they are an INTEGRAL part of the hydraulic engineering courses. It is intended to draw to the student's attention the behaviour of real fluids. Each experiment relates to the fluid mechanics of open channel flow. The basic concepts of critical flow conditions, subcritical flow and supercritical flow are experienced. Note that one experiment (broad-crested weir) is a smooth transition from an upstream sub-critical flow to a downstream supercritical flow (Fig. 1). The other (hydraulic jump) is the transition from an upstream supercritical flow to a downstream subcritical flow (Fig. 2). Fig. 1 - Sketch of a broad-crested weir overflow
Fig. 2 - Sketch of a hydraulic jump flow
CIVL3140
EXPERIMENT : BROAD CRESTED WEIR 1. AIM The purpose of this experiment is to investigate : - rapidly varying flow in the vicinity of a broad-crested weir. - flow transition between sub-critical and super-critical flows, and - the basic concepts of hydraulic controls, specific energy and Bernoulli principle applied to open channel flows.
2. INTRODUCTION TO BROAD-CRESTED WEIRS In hydrology, it is desirable to have long historic records of streamflows to predict the extremes : i.e. low-flow (or drought) and high flow (floods). Because quantifying flow rates is difficult, but measuring water-levels is easy, the strategy at a stream-gauging station is to measure water-levels continuously and calibrate a stage-discharge curve to convert heights into flow rates. A randomly selected stream location is unsatisfactory for gauging purposes because, for any given water height, the flow rate when a flood is rising is greater than when it is receding. An alternative is the construction of a weir in the stream channel to force critical depth conditions to occur. This results in a satisfactory monotonic relationship between flow rate and flow depth at the weir. In most practical situations, the approach flow velocity is small and the upstream flow conditions are sub-critical. However, on the immediate downstream side (provided the outlet is not "drowned" by some further downstream structure or hydraulic control phenomenon), the flow discharging from the weir crest will generally be supercritical. In crossing the weir, therefore, such flow must pass through CRITICAL flow conditions : i.e. the specific energy must reach a minimum. A weir is called "broad-crested" when the crest is long enough for the streamlines to be parallel to the crest invert, the pressure distribution to be hydrostatic and critical flow conditions to occur somewhere over the horizontal section of the crest. Besides investigating the position at which critical flow depth occurs (and if possible explaining why), it is useful to study the changes in specific energy that take place as the flow passes over the weir. If the energy loss is negligible in passing the sill crest, one should remember that the specific energy above the crest must be less than that upstream by the height of the step because specific energy is referenced to the local channel bed elevation (see definition of the specific energy).
3. PREREQUISITES 3.1 At least 1 day before the scheduled lab session, visit the laboratory, inspect the apparatus, and prepare a preliminary sketch of it. 3.2 Express the relationship between the specific energy, the discharge, channel width and depth in a horizontal rectangular channel. 3.3 Sketch a broad-crested weir flow in a horizontal rectangular channel. On your sketch, plot the free-surface profiles upstream, above and downstream of the weir. Indicate the flow direction. Sketch on your figure the variation of the pressure with depth at a section 1 (upstream of the weir), a section 2 (at the middle of the weir crest) and a section 3 (downstream of the weir). At sections 1, 2 and 3 , the velocity is assumed to be essentially horizontal and uniform. 3.4 In the horizontal rectangular channel, derive the relationship between the discharge, the upstream specific energy, the channel width and the weir height. 3.5 For a horizontal channel of rectangular cross-section, develop the dimensionless expression of the specific energy E/dc as a function of the dimensionless flow depth d/dc, where dc is the critical flow depth. Note : the resulting non-dimensional relationship is universally useful for studying any transition in any channel.
4. APPARATUS In the upper laboratory, three 3.2 m long rectangular horizontal channels are supplied with water from the constant head reservoir. The discharge is controlled by a valve mounted just above the head tank at the upstream end of the channel. Each channel are fitted with horizontal side rails and water depths are measured using mobile pointer-gauges. About halfway along the channels, a section of the floor is raised to form a weir platform (with a flat sill, about 42-cm long in the flow direction). The weir's upstream vertical face is rounded where it meets the horizontal sill, while the downstream face is fitted with a tapered downslope (ramp) that lowers the flow back to the original channel floor level
CIVL3140
in a smooth concave-upward curve. A profile of the weir is provided to assist in plotting the experimental flow profiles. At the downstream end of each channel, the normally free-fall outlet is fitted with an adjustable gate, which can be cranked downward into the outflow to force a hydraulic jump to form if it is desired to investigate when the weir becomes "drowned". Channel flow rates are measured by timing a specified "weight" of outflow in the channels 1 and 2. The outflow falls into a separate tank mounted on a weighing platform with a balance arm to which counter-weights can be added. Under steady-flow conditions, with the tank's lever-action outlet valve wide open, the water level in the tank rises until its outlet discharges at the same rate as the tank inflow. If counter-weights are THEN used to just exceed the effect of the tank contents, the balance arm falls to its "LOW" position. If the tank outlet is then closed, a timer may be started as soon as the balance arm moves to "HIGH". By THEN (quickly) adding a known EXTRA counter-weight to return the balance arm to "LOW", the timer may be stopped as soon as the next "HIGH" move indicates that the specified EXTRA water has entered the tank. In the channel 3, the water discharge is measured with a calibrated orifice meter. The calibration curve of the orifice is plotted next to the channel intake section. Comments Note how water depths in the channel are measured using pointer-gauges with vernier scales. Each vernier scale needs to be set to read zero when the pointer is at the current channel floor level, upstream of the crest. [One pointer-gauge may be set for use over the horizontal sill.] Remind yourself how to interpret the particular vernier scales. Check with your fellow group-members that you all read them the same way. Familiarise yourself with the outlet weighing system, noting the values of the counter-weights provided. Without water flowing, ensure that each member of your group understands the sequence of operations needed to measure flow rates using the apparatus and procedure outlined above. Figure out what circumstances would cause (a) the channel, and (b) the outlet tank, to spill over the lab floor.
5. REFERENCES CHANSON, H. (2004). "The Hydraulics of Open Channel Flow : An Introduction." Butterworth-Heinemann, Oxford,
6. Additional bibliography CHANSON, H. (1999). "The Hydraulics of Open Channel Flow : An Introduction." Edward Arnold, London, UK,
512 pages (ISBN 0 340 74067 1). CHANSON, H. (2006). "Minimum Specific Energy and Critical Flow Conditions in Open Channels." Journal of
Irrigation and Drainage Engineering., ASCE, Vol. 132, No. 5, pp. 498-502 (ISSN 0733-9437). GONZALEZ, C.A., and CHANSON, H. (2005). "Experimental Measurements of Velocity and Pressure Distribution
on a Large Broad-Crested Weir." Flow Measurement and Instrumentation, Vol. 18 (DOI 10.1016/j.flowmeasinst.2007.05.005) (ISSN 0955-5986).
HENDERSON, F.M. (1966). "Open Channel Flow." MacMillan Company, New York, USA. ISAACS, L.T. (1981). "Effects of Laminar Boundary Layer on a Model Broad-Crested Weir." Research Report No.
Design Considerations, Balkema Publ., Rotterdam, The Netherlands, 249 pages. MONTES, J.S. (1998). "Hydraulics of Open Channel Flow." ASCE Press, New-York, USA, 697 pages. NOVAK, P., MOFFAT, A.I.B., NALLURI, C., and NARAYANAN, R. (2001). "Hydraulic Structures." Spon Press,
London, UK, 3rd edition, 666 pages.
CIVL3140
Laboratory classes CIVL3140 Introduction to Catchment Hydraulics
Pre-requisite calculations
EXPERIMENT : BROAD CRESTED WEIR Date (Week and day) : Student's Name : Specific energy : E = Derivation :
Sketch of the broad-crested weir overflow
CIVL3140
Discharge : Q = Derivation :
Dimensionless specific energy : Edc
=
Derivation :
CIVL3140
EXPERIMENT : HYDRAULIC JUMPS 1. AIM The purpose of this experiment is to study the behaviour of a hydraulic jump and to quantify the characteristics of stationary hydraulic jumps (e.g. downstream flow depth, rate of energy dissipation) over a range of Froude numbers (see textbook, pp. 53-63 for the basic equations).
2. INTRODUCTION TO HYDRAULIC JUMPS A hydraulic jump is a stationary transition from an upstream supercritical flow to a downstream subcritical flow. Remember that the broad-crested weir induces the reverse flow transition : i.e., from an upstream subcritical flow to a downstream supercritical flow Under steady conditions, the forces tending to push it downstream must balance those opposed. If the jump is considered a free body, it is relatively easy to identify (and by experiment quantify) the pressure forces and momentum flux at the upstream and downstream ends of the control volume. Some hydraulic jumps appear like smooth (undular) waves with almost negligible turbulent activity, but most involve a vigorously tumbling flow region within which much kinetic energy is being "lost" (converted into heat). The latter type of jump is often employed as an energy "dissipator" (below a dam spillway, for example) to avoid scour of bed material in high velocity regions that might otherwise occur if the kinetic energy of the flow is not dissipated. 3. PREREQUISITES 3.1 At least 1 day before the scheduled lab session, visit the laboratory, inspect the apparatus, and prepare a preliminary sketch of it. 3.2 Sketch a hydraulic jump flow in a horizontal rectangular channel. On your sketch, plot the free-surface profiles upstream and downstream of the jump and indicate the flow direction. Sketch on your figure the variation of the pressure with depth at a section 1 (upstream of the jump) and a section 2 (downstream of the jump). Sections 1 and 2 are located far enough from the sluice gate for the velocity to be essentially horizontal and uniform. 3.3 Apply the continuity, momentum and energy equations to a hydraulic jump in a prismatic rectangular channel : In the textbook, find the dimensionless expressions of the downstream flow conditions (depth, Froude number) and rate of energy dissipation, as a function of the upstream Froude number Fr1 : 4. APPARATUS In the upper laboratory, three 3.2 m long rectangular horizontal channels are supplied with water from the constant head reservoir located about 2.5 m above floor level. The reservoir feeds a head tank which then feeds each channel with a supercritical flow through a vertical sluice-gate. Normally, the opening of this sluice-gate will have been preset to 20 mm for this experiments. The 0.45 m deep channels are fitted with horizontal side rails so that water depths upstream of the jump can be measured using a mobile pointer-gauge. At the downstream end of each channel, the free-fall outlet is controlled by an adjustable overflow gate, which can be cranked above the channel floor to force a hydraulic jump to form under steady conditions about 2 meters upstream of the channel outlet. Discharge measurements are made with either a 90-degree V-notch weir [The calibration chart for the V-notch weir is located on the side of the inlet tank] or a Venturi manometer [The discharge is related to the head loss by a calibration curve given]. Comments Investigate the discharge measurement system of the flume : + For the V-notch weir measurement, note how water levels are measured in the V-notch-weir tank by means of a hook gauge and vernier scale. The vernier scale needs to be set to read zero when the water level is at exactly the same level as the apex of the notch. In the time since this tank was last used, the vernier scale setting will probably have been tampered with, AND some water will have evaporated so that the tank water level is not at notch level. Check this last point by viewing the weir from its inlet side to see if the reflection of the V-shape in the undisturbed
CIVL3140
tank contents lines up with the weir itself. If the tank contents need topping up, a hose or bucket may be used. If too much is added, the tank has a valved outlet drain. Remind yourself how to interpret the vernier scale. Check with your fellow group-members that you all read it the same way. + For the Venturi measurement, note the location where the head loss measurement is made. Note that the head-tank contents are indicated by means of a manometer tube close to the tank's outlet and on the rear of the tank so that it may be viewed from the operating position for turning on the water supply valve. The valve must be set to supply water at exactly the same rate as it is being discharged through the sluice gate, which depends on the height of the water level inside the tank. Figure out what circumstances would cause (i) the channel, and (ii) the head tank, to spill over the lab floor.
5. REFERENCES CHANSON, H. (2004). "The Hydraulics of Open Channel Flow : An Introduction." Butterworth-Heinemann, Oxford,
6. Additional references CHANSON, H. (1999). "The Hydraulics of Open Channel Flow : An Introduction." Edward Arnold, London, UK,
512 pages (ISBN 0 340 74067 1). CHANSON, H. (2007). "Bubbly Flow Structure in Hydraulic Jump." European Journal of Mechanics B/Fluids, Vol.
26, No. 3, pp.367-384 (DOI:10.1016/j.euromechflu.2006.08.001) (ISSN 0997-7546). HAGER, W.H. (1992). "Energy Dissipators and Hydraulic Jump." Kluwer Academic Publ., Water Science and
Technology Library, Vol. 8, Dordrecht, The Netherlands, 288 pages. HENDERSON, F.M. (1966). "Open Channel Flow." MacMillan Company, New York, USA. MONTES, J.S. (1998). "Hydraulics of Open Channel Flow." ASCE Press, New-York, USA, 697 pages. NOVAK, P., MOFFAT, A.I.B., NALLURI, C., and NARAYANAN, R. (2001). "Hydraulic Structures." Spon Press,
London, UK, 3rd edition, 666 pages.
CIVL3140
Laboratory classes CIVL3140 Introduction to Catchment Hydraulics
Pre-requisite calculations
EXPERIMENT : HYDRAULIC JUMP Date (Week and day): Student's Name :
Hydraulic jump sketch
CIVL3140
Basic equations
Give the expression for the alternate depths as a function of the other depth and discharge, or as a function of the Froude numbers. Write the energy loss in terms of the energy equation either side of the jump.
[C]
[M]
[E]
CIVL3140
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EXPERIMENT : EQUILIBRIUM AND NON-UNIFORM FLOWS IN A LONG CHANNEL
1. AIM
The purpose of this experiment is to demonstrate the effect of open channel control features on gradually-varied flows,
and to quantify friction and backwater effects that occur differently in "steep" and "mild-sloped" waterways carrying
steady flows. The experimental procedure will include observations, modelling, prediction (numerical modelling) and
evaluation (comparison between data and computation).
During the afternoon, the students will be involved in physical modelling and experimental observations, numerical
modelling, and a comparison between physical and numerical model tests. Each experiment will be supported by an
audio-visual technical documentary ("Surfing the Dordogne" 2006).
2. UNIFORM EQUILIBRIUM AND GRADUALLY VARIED FLOW
2.1 Introduction to ungated flow
Flow enters the channel via a low-velocity stilling basin, then it gradually accelerates down the sloped channel.
Because the flow rate is steady, the flow depth gradually decreases with increasing velocity. As shear stresses gradually
increase with increasing velocity, the inertial acceleration is eventually balanced by frictional deceleration, yielding
uniform equilibrium flow of depth do. (Note that do is called the normal depth).
One might expect to measure normal depth somewhere near the downstream end of the channel, but before doing so,
we need to consider the effect of the overfall at the downstream end of the channel. If the channel slope is steep, the
uniform equilibrium flow regime will be supercritical, and information about the downstream "waterfall" cannot be
propagated upstream against supercritical flow. So near the outlet is a good place to look for do if the channel slope is
steep. However, if the slope is mild, normal flow will be subcritical, and critical depth must occur at or near, the
overfall as the free-falling nappe is an accelerating supercritical flow (see HENDERSON 1966, pp. 192-195).
"Backwater effect" from the hydraulic control (i.e. critical flow depth) at the overfall will be "conveyed" upstream to
the approaching flow in the form of a backwater curve. In this case, the best place to look for do is upstream of this
backwater curve i.e. probably near the middle of the experimental channel.
References : CHANSON (2004), pp. 100-106; HENDERSON (1966), pp. 38 to 44.