LABORATORY FACILITIES

Primarily, a hydraulics laboratory must be designed for the student's practical experience in topics related to conventional hydraulics courses, special projects, regular courses or for research introduction. It is very difficult to recommend the best facilities and dimensions for an educational hydraulics laboratory because they depend on many local factors. These include the degree of interest in hydraulics in the courses, space availability, the insti-tution's budget, the number of teachers, the number of students and also the eventual possi-bility of basic and applied research activities. In many cases it will be possible to use existing installations and to modify or to extend them.

3.5.1. General Layout

A covered space of 15 m width and 40 m length has reasonable dimensions for an educational hydraulics laboratory. The laboratory area can be reduced if the number of students is small and if not all of the educational models described in this monograph are installed.

A separate water circuit must be provided for the educational laboratory. It will be composed of the external water supply, a reservoir with an appropriate filter, a pump station, a constant level tank with several outlets, and pipes for water distribution and return

channels. A suitable discharge capacity is 100 1/s, but more discharge capacity is always desirable in order to allow for future laboratory expansion. For 100 1/s discharge, the storage reservoir must have more than 100 m usable volume and the constant level tank must have a volume of 8 m or more. The tank must be placed at least 4 m above the floor. It is better to have several pumps of different sizes in the system rather than only one big pump.

For different design discharge rates it is possible to calculate the reservoir and tank volumes with the same ratios. It may be necessary to have a small auxiliary pump to empty the reser-voir, and also it is necessary to anticipate the disposal of the used water. The length of the weirs in the constant level tank must be calculated in order to minimize discharge

fluctu-ations. The overflow pipe must have an adequate capacity.

If•there is a river near the laboratory, a gravity water supply system may be possible.

This will call for certain changes in the water supply system. The water distribution to different points i'n the laboratory can be done either by overhead pipes or underground pipes fitted into small trenches covered by prefabricated slabs. The former is easier to construct and to identify the conduits, but the second method is generally tidier and more functional.

The laboratory floor must have a small slope towards the boundaries, where small gutters must be installed. All water losses, overflows, and cleaning water will go to the gutters, and then out of the laboratory. Special consideration should be given to the lighting of the hydraulics laboratory. This is of particular importance for laboratories intended for re-search. A small workshop is required for the construction of small educational models, for mechanical repair of laboratory facilities and for general maintenance. Usually, an educa-tional laboratory will not need complex workshop facilities. Wood, acrylic and metals are the common materials, and only ordinary equipment is needed. A small welding machine, a good set of tools, an electric drill, etc., are obviously essential devices.

3.5.2. Flow in Pipes

An educational laboratory can easily have good, inexpensive models to show clearly flow phenomena in closed conduits. General examples include the practical demonstration of laminar flow, friction factor, transverse velocity distribution, local energy losses, and unsteady flow in pipes.

The laminar flow experiment can be performed with a closed circuit filled with oil and served by a small pump. The main part of the circuit is a tube 50 cm long and 5 mm in diameter with piezometers at each end.

An experiment with theoretical and practical applications is the determination of friction factors for smooth pipes at different Reynolds Numbers. If the object of the experiment is to demonstrate the transition from laminar to turbulent flow, a careful design of the equipment is required. One possibility is to use a constant level tank movable vertically over several meters. Alternatively, the pipe under test is connected via a good throttling valve to the controlled water supply of the laboratory. The pipe tested may be a glass tube 2m long and 5 mm in diameter.

The experiment to determine the transverse velocity profile of steady flow in pipes requires a pipe of at least 10 cm diameter with an undisturbed length of 50 diameters or more so that a boundary layer can be developed. The instrumentation needed is a small Pitot tube or

a hypodermic needle and means to move it across the pipe. Another closed conduit experiment, suitable for the laboratory, is the verification of the local energy loss at a sudden pipe enlargement. The equipment needed is several piezometric tubes connected to the pipe before and after the enlargement. Additional piezometers should be located in the ring-shaped section of the enlargement to demonstrate that the pressure in this section is different than that of the small diameter pipe (see Fig. 3.5). The experimental results can be checked with the theoretical equation and published values.

Local losses can also be illustrated in other models. In this group, discharge pipe meters such as orifices, nozzles, bends, etc. can be considered. A general model for energy

loss measurements in conduits can be constructed in the laboratory workshop with several pipes of different diameters, bends, valves, venturimeter, nozzle, orifice meter, and other

accessories. This equipment can also be bought. Special manufacturer's catalogues should be consulted.

An experimental demonstration of unsteady flow in closed conduits is an optional project.

The model requires a surge tank in the form of a vertical cylindrical, transparent tank of approximately 25 cm diameter and a long pipe of about 5 cm diameter the length of which must carefully calculated. It also requires a quick acting valve at the end of the conduit. It is desirable to have an electromechanical system to control the valve closure. Instrumentation for measuring fast level fluctuations, as described in Section 3.3.1 must be used for recording water level oscillations.

3.5.3. Flow in Open Channels

Many open channel experiments can be carried out in a multipurpose horizontal flume which can be designed and constructed by the laboratory staff. Such a flume should be 40 to 80 cm wide and 30 to 60 cm deep and between 6 and 12 m long. The flume should be equipped with an entrance box and means to regulate the inflow and a gate at the downstream end to regulate the depth of flow. Examples of experiments that can be carried out in this flume include the hydraulic jump (Fig. 3.6), flow at open chanel contractions and expansions, effects of a sill, etc. The horizontal flume can also be used for hydraulic structures models tests.as described in Section 3.5.4.

A glass-walled flume with variable slope is also useful for open channel flow experiments.

This kind of equipment can be bought, selecting from different models constructed by special manufacturers. Flume dimensions depend on laboratory requirements, but the following dimen-sions for a tilted laboratory flume are typical: 15 cm to 25 cm width, 40 cm to 60 cm height, 6 m to 10 m long. The slope ranges can be from +10% to -3%. Obviously, all dimensions are larger than the dimensions of the small flume intended for classroom demonstration, described in Section 3.4.4. The maximum discharge will be from 60 1/s to 100 1/s. This piece of equip-ment will generally define the capacity of the general water supply system.

The tilting flume can be used for the experiments described above for the horizontal flume, however it is more useful for experiments in mobile bed flow, introducing different granular materials. Students can then observe ripples, dunes and perhaps antidunes, and they can also verify the conditions of initiation of motion. The design of the sediment recir-culation system must be done very carefully. Perhaps the best solution is to have a special flume for sediment motion studies.

3.5.4. Hydraulic Structures

With a relatively low cost the laboratory may have a fixed slope flume with glass panels and horizontal concrete floor. This channel usually has larger dimensions than the tilting flume. It can be used for many experiments, some of them similar to those described for the other flumes. However, this flume is suitable for verification experiments of various

hydraulic structures such as splitters, spillways, stilling basins, bridge piers, sluice gates, etc. (Fig. 3.7).

A two-dimensional physical model of a high overflow spillway in the fixed slope channel may be used to show the flow action over several structures, because the spillways may have piers, tainter gates, chute blocks and an energy dissipator. If the channel width is 50 cm to 60 cm the model may contain a central gate bay, two piers and two half spillway gate bays. This experiment is more useful if the students have previously computed the theoretical discharge, pressures; pier contraction effects and dissipation efficiency.

3.5.5. Pumps and Turbines

A separate section of the laboratory should be reserved for hydraulic machinery models.

These installations are too complex to construct in a laboratory workshop, and special

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manufacturers have compact equipment available, with the possibility of choosing between several different installations.

The centrifugal pump is the most widely used type of hydraulic machine. All engineers need tc be acquainted with its operation and performance characteristics. In many instal-lations more than one centrifugal pump is employed operating either in parallel for high flow rates or in series for high discharge pressures. In some cases it is possible to use the circulating pumps of the hydraulics laboratory for the pump test experiment. Pre-designed pump test sets are available with two or more identical centrifugal pumps. Generally, the following instruments are provided: several pressure and vacuum gauges, venturimeter, manometers,

V-notch weir, rectangular weir, ammeters, voltmeters, tachometer and torque meters for the pumps. The equipment may be used to test a single pump or for an advanced test using both pumps. The experiments available are the following: head-discharge curves at various pump speeds, pump efficiency curves, derivation of iso-efficiency curves, study of two pumps in parallel, study of two pumps in series, and comparison of power measurement by electrical and mechanical methods. The students may calculate the theoretical performance of the pumps and compare this with the results they obtain during experiments. In some cases it is possible to use the circulating pumps of the hydraulics laboratory for the pump test experiments.

Turbine model sets for educational purposes are designed by several special manufacturers.

There are models for Pelton turbine tests, for Francis turbine tests and for Kaplan turbine tests. Compound models are also available, such as the universal radial flow machine apparatus for testing the performance of a single centrifugal pump, two pumps in parallel or series, a small reversible pump-turbine, etc. Manufacturer's catalogues may be consulted for more information.

3.5.6. Hydraulic Models

The installation and use of a comprehensive hydraulic model as an educational facility is desirable. It is outside the scope of this monograph to discuss hydraulic similarity laws and the basis of physical model design and operation. The use of a Froude model of a real or imaginary watercourse is suggested. The simulation of different hydraulic structures can be tested in this model.

A suitable model can represent a multipurpose dam, with a powerhouse intake, a spillway, energy dissipators, outlet structures, locks, erosion protection works, etc. Students can test the different structures when subjected to normal and flood flow, and also the interaction between various structures. This model is a good opportunity to use measuring equipment. The model may also be used to show a dam's operation and the effects of human activity on the watercourse.

Movable bed models allow for local scour visualisation. Bridge piers may be placed on the movable bed river section, downstream of the energy dissipation structures in order to see the local erosion around the piers. Sediment scales can be obtained from hydraulic model books.

If it is not feasible to obtain movable bed similarity the use of any erodible coarse material, including specially manufactured artificial sands, is possible. The results obtained are qualitative but very useful to show the students a vivid picture of the effect of fluvial hydraulic works. Morphological, fluvial and tidal studies may need distorted models and artificial roughness.

3.5.7. Flow Visualisation

Many experiments can be used to visualise streamlines, vortex formations, separation effects, flow patterns, velocity profiles, etc. For this purpose there are certain techniques of flow visualisation used in hydraulics and fluid mechanics research. Different techniques are connected with the type of element used as trace for the visualisation and, of course, with the recording system.

Tracers can be liquids, solids or bubbles. Liquids used are generally made with soluble dyes in water. There are many chemical dyes with different characteristics for different uses.

Each laboratory has its own selection and preference. Solid tracers are usually floating elements for surface trajectories in open channel flows, see Fig. 3.8. Tracers range from sophisticated floating lights to simple confetti made from small perforations of computer cards. Flow visualisation in the fluid can be done with solid tracers, the best known of them is aluminium powder.

If the flow has air entrainment (a hydraulic jump or high velocity flows) air bubbles can be efficient natural tracers. Sometimes, for photographic or cinematographic reasons, arti-ficial bubbles must be included into the fluid. This can be done by the addition of a quantity of detergent, but if detergents are used the quantities must be very small to avoid contami-nation of the water supply of the laboratory.

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Flow visualisations can be performed for student view or for graphic records. Cinemato-graphic camera and other diverse photoCinemato-graphic equipment are the usual recording systems. In any case, the illumination and the classroom conditions are very important. The use of cameras with instantaneous development is useful for educational purposes.

3.5.8. Calibration Facilities

One of the important functions of a hydraulics laboratory is the calibration of measuring devices used in hydraulics, mostly flow measuring instruments. Calibration is a process whereby a correlation is established between the readings of the measuring device and the corresponding true value of the variable measured. A prerequisite for actually carrying out a calibration process is the ability to determine the true value of the variable considered by some independent means or instruments that yield results with better precision, than that of the instrument being calibrated. It is obvious that the more accurate instruments used as

standards of comparison also need to be calibrated from time to time. Special attention should be given to the correct setting of the zero reading of the measuring device being calibrated.

The calibration should span the full range*over which the device is expected to operate.

The calibration facilities of a hydraulics laboratory are provided usually as a commercial activity which is also a service to industry. The inclusion of such facilities in a teaching laboratory has important educational aspects. It can be used for establishing the concepts of precision and accuracy, and for teaching the correct procedures of using various measuring devices. The facilities are, of course, also used for teaching the calibration procedures of various instruments.

The most important calibration facility of a hydraulics laboratory is a set of precise volumetric containers for the calibration of water meters and discharge measuring equipment.

The volumetric containers range from small and medium size precision flasks to large accurate volumetric or weighing tanks which can be designed and built as part of the laboratory

structure. The flasks measure only one fixed volume, while the volumetric or weighing tanks have scales that enable the accurate determination of volumes of water smaller than the capacity of the tanks. These tanks also require calibration after being constructed or installed in the laboratory. In some cases this may require the use of a specially con-structed, relatively large flask which delivers accurately known quantities of water to the tanks. A precaution recommended in all volumetric work is to record temperatures and to make allowance for volume changes if applicable.

The main use of the volumetric calibration containers is for calibration of instruments and equipment for measuring volumes and rates of flow. These can range from instruments for measuring domestic water supplies to flumes and weirs used for discharge measurements in streams. Large measuring flumes may require the use of an intermediate accurate flow meter which is calibrated with the aid of the volumetric tank and is then used to calibrate the flume. For measuring rates of flow the volumetric tanks are used with precise stop watches or other time measuring instruments.

Other calibration facilities in a hydraulics laboratory include equipment for calibration of flow velocity meters, pressure gages, moisture probes, etc. If a separate hydrological laboratory is available some of these facilities may be located in the hydrological laboratory.

Thus, a towing tank which is used for calibration of current meters may be part of a hydraulics laboratory or it could be included in a hydrological teaching facility (see Section 4.2.3).

The maintenance of the calibration facilities of a hydraulics or a hydrological laboratory should be carefully planned and periodically carried out. The purpose of such a maintenance program is to maintain a high standard of precision obtainable with the calibration facilities.

Special records should be kept of the factors which may affect the performance of the cali-bration equipment. The records should include plans and specifications of the equipment, as well as installation and calibration notes. A program of periodic checks of the calibration equipment should be prepared and the results of such checks should be kept on file with other records of each calibration instrument.