Armfield Engineering Education

APPLIED HYDRAULICS AND HYDROLOGY

Hydraulic Research Equipment - Issue 1

 

Special Laboratory Flumes, Channels, Tanks and Basins for
Hydraulic Teaching/Research Studies

The, long association of the company with applied water hydraulics and fluid mechanics has led to the design and installation of a number of research facilities, according to customers' requirements.

In recent years, the following types of equipment have been supplied:

• Large open-channel flow systems for studies in
sediment transport, water waves, and hydraulic structures.
• Wave flumes, both for random or regular waves, together
with beaches and instrumentation.
• Coastal engineering model basins, for the study of naturally
occurring situations as well as harbour and sea defence models.
• Computerised towing carriage systems.

The Key Features of an Open Channel Facility

Because of the physical size and the general heavy nature of the construction, it is easy to forget that a flume is an instrument and in many instances required to have a high level of integrity regarding both its working dimensions and ability to achieve repeatable results.

Armfield acknowledge the necessity for accuracy, precision and repeatability. These are cornerstones of the design, manufacture and final installation.

Dimensions

The critical dimensions of a flume are the working length and cross-section (width and depth). Working length also means usable length. All too often the turbulent entry conditions require a substantial portion of what would be described as the working section before suitable flow conditions prevail. Armfield flumes are designed such that the working length is maximised. The overall dimensions of the flume are also minimised through careful design of the inlet and outlet conditions and sensible use of the space underneath the flume and immediately adjacent.

Materials of Construction

The materials of construction are of paramount importance, not only for the durability and longevity required of an expensive piece of equipment, but also suitability for purpose. Many flumes are used for sediment transport studies and therefore the materials in contact with the sediment must have abrasion resistance. In such instances it is standard practice for Armfield to incorporate stainless steel on the bed of flumes.

Clarity of flow visualisation is an essential ingredient, particularly if laser doppler anemometry or sophisticated photography is involved. Even potable water will abrade a surface but water containing harsh particles, such as sediment, will quickly damage any soft material. This is why all Armfield flumes are constructed with toughened glass viewing panels, whether these be small portholes or full length working sections. Toughened glass is also used as a safety feature. In the unlikely event that a glass panel shatters, it will not break into dangerous sharp shards but into small relatively harmless cubes.

Wherever possible the more basic components in contact with water are made of non-corroding materials, such as plastic or GRP. Pumps are usually steel but where sediment is involved we recommend the use of special pumps, typically glass lined. Where wood or a composite material is chosen for the base and/or sides of the flume, these are carefully treated to protect against water ingress.

Set-up and Assembly

Armfield flumes, whether a standard product or customised, are built on a modular principle. This allows them to be delivered to site in pre-fabricated, manageable sections. The designs are such that in most cases with help from the instruction manual, clients are able to assemble and commission the equipment without the need for our skilled staff. However this is always an option, and Armfield are happy to submit a quotation for installation, commissioning and, where appropriate, basic training.

Ease of Use

Experimentation can be a time-consuming and tedious business. Quite often long periods are required in order to gather sufficient meaningful data. It is at these times that the user appreciates equipment that has been carefully designed from an ergonomic viewpoint.

Armfield incorporates many features to ease the life of the operator. All controls on a single floor mounted console. Electrical options for driving valves, jacking systems and weirs. Direct reading flow meter instrumentation, with digital readout at the control console. Powered instrument carriages offering three way axes. A sensible working height that provides comfortable access to the working section.

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Hydraulics: Performance and Systems Design

 

Uniform Flow

Within the limited confines of a laboratory flume it is critical that the best possible working conditions are achieved as quickly as possible after the flow enters the working section. Much hinges on the entry conditions and particularly the means used to settle and direct the flow as it enters the inlet tank and is re-directed into the working section.

Inlet Tank Design

The inlet tank design generally adopted as standard by Armfield is the consequence of 40 years of experience coupled with comprehensive model test work. The result is a carefully shaped tank, with profiling to both the side walls and base, whilst remaining compact in its length, an essential ingredient to minimise the waste of laboratory space. Within the tank various stilling devices are incorporated.

Level Control - The Outlet Weir

Of equal importance is the method of controlling the level within the flume. This is usually done through a weir at the discharge end. Many options exist but most frequently Armfield utilise either an adjustable overshot tilting weir or, for more complex flow conditions, a venetian blind weir with either vertical or horizontal slats.

Water Supply

Traditionally hydraulic laboratories were constructed with underfloor sumps and elevated header tanks linked with a ring main. Modern laboratories rarely enjoy these facilities. Armfield are, however, able to supply flumes either in a non self-contained configuration, where they can be serviced from an existing header tank and discharge to a laboratory sump, or as fully self-contained facilities, where floor mounted reservoirs, pumps, pipework, valves and flow meters are incorporated, including, where appropriate, re-circulating loops for sediment transport.

Occasionally flumes are required that meet both requirements. These can also be supplied.

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Experimental Models & Instrumentation

A selection of instruments is available for use in flumes
channels and basins:

H1- 1 to H1-11 Vernier Hook & Point Gauges
H12-1 to H12-7 Manometers including water, pressurised, water-mercury
H12-8 to H12-9 Portable Pressure Meters
H30-1H to H30-3H Pitot Tubes
H32 Turbulence/Velocity Meter
H33 to H33-8 Velocity Probes, Indicators and Recorders
H40-1-1 to H40-2-3 Wave Probe Systems

Individual detailed catalogues available on request.

A comprehensive range of experimental models and measuring instruments is available for selection. These provide the basis for a large number of practical experiments in open channel flow including the use and operation of regulating and gauging structures.

Wherever possible non-corroding materials have been used to reduce maintenance time and increase the working life of the models.

S6-20: Plate Weirs - (Stainless steel)

> screw operated adjustable undershot weir
> rectangular overshot weir plate
>`V´ notch weir

S6-21: Broad Crested Weirs - (GRP)

> rectangular sharp cornered weir
> rectangular streamlined weir

S6-22 Venturi Flume - (GRP)

A set of GRP mouldings for installation in the channel section to form a venturi flume.

S6-23: Ogee Weir & Manometer Board - (GRP)

Eight pressure tappings (2 upstream, 5 downstream, 1 at apex) complete with multi-tube piezometer board.

S6-24: Dam Spillway Models - (GRP)

Complete with the following interchangeable downstream sections:
> spillway toe
> roller bucket toe
> apron with removeable energy dissipator

S6-25: Syphon Spillway - (Acrylic)

Complete with adjustable breather tube.

S6-26: Self-regulating Syphon -(Acrylic)

S6-27: Roughened Beds - (GRP)

Two sections of different roughness. Each consists of three modules arranged to cover a 2.5m length.

S6-28: Vibrating Pile

For the study of vortex shedding by piles and tall structures.

S6-29: Lift & Drag Balance & Models - (GRP)

Three models - large and small diameter cylinders and an aerofoil section.

S6-30: Pitot Tube & Manometer Board - (GRP)

Complete with traversing carriage and vernier height adjustment, and an inverted paraffin water manometer for magnification of small pressure differences.

S6-31: Crump Weir - (GRP)

Single pressure tapping at apex, complete with piezometer tube.

S6-32: Parshall Flume - (GRP)

One of the most widely used standing wave flumes; allows comparison of head-flow characteristics with those published in the literature.

S6-33: WSC Flume - (GRP)

Developed by Washington State College, this trapezoidal flume conforms more closely to natural channel sections and passes sediment even more freely than the Parshall Flume.

S6-35: Wave Generator

Simple, regular, flap-type generator designed to be mounted on the flume discharge tank.

S6-36: Beach

S6-37: Zagni Flow Monitoring

System Consists of a free standing manometer board and instrument carriage fitted with Pitot tube and interconnecting tubing. This system may be used to establish the basic parameters of fluid flow in the channel including, invert slope, surface profiles, pressure profiles and velocity profiles.

S6-40: Instrument Carrier

Both longitudinal and transverse movement and position lock.

S6-42: Velocity Meter and Mountings

Velocity probe and analogue meter, complete with mounting attachments to channel. Range 0.6 to 3m/sec.

H-1: Hook & Point Gauge

Designed to be mounted on S6-40.

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Wave Generators

Wave generation and the effects of waves are significant areas of study. Wave generators themselves can range from simple mechanical systems for regular waves through multi-paddle random generating systems that may be computer controlled. For many applications, particularly coastal models and flume studies, long crested and directional random waves are sufficient to model the sea state. For offshore studies and some shallow water problems multi-directional components are required.

In flumes or open channels, such as described in this brochure, there are a number of different types of wave maker that are appropriate. For small scale laboratory installations electrically driven piston machines are available. Where larger flumes are involved hydraulic powered piston machines and for deeper water, wedge type wave makers. Flumes may be used to study breakwaters, sea walls and beach behaviour, or for fundamental research.

Multi-element wave makers recreate complex short crested waves. Many wave makers of this type have hinge-flap type paddles and are used, for example, in offshore sea basins where models of oil and gas rigs are tested. For shallow water piston mechanism is the preferred mechanical option.

Whatever the application Armfield can supply a complete system designed to suit your particular requirements.

S6-45 Random Wave Maker

This machine utilises the base hinge weir in the discharge tank of the Armfield S6 Flume as the paddle. The S6-45 Control box interfaces with a personal computer (not supplied by Armfield) via a serial interface.

Wave generation software

> Regular waves
> Irregular waves - filtered white noise
> Irregular waves - Fourier series
> User defined wave generation techniques

This is an advanced software package designed to simulate long crested sea conditions. It can generate Regular, Irregular and Solitary waves.
It is capable of running on any Windows compatible-PC with a free serial interface.

Installation is by means of an installation program. Following installation it allows all the relevant dimensional details of the paddle to be entered and saved in a file.

The experimental transfer function can be entered and saved for a range of water depths.

Wave height and period requirements are entered at full (prototype) scale together with the model scale being used.

When it is running, the parameters of the generated sea state and a real time graphical display of the paddle movement are shown on screen.

For more information on S6-45 request data sheet S6-45 provisional

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Special Tilting Flumes

Many areas of study require or are enhanced by using flumes with a tilting capability. This mostly translates into positive slope but sometimes there is the requirement for negative slope.

The most important aspect of a tilting flume is retaining the integrity of the working section, i.e., maintaining tolerances.

To achieve this requires an extremely rigid design which ensures almost no deflection regardless of load or tilt. Design of the jacking system is crucial in guaranteeing this.

The general construction of such flumes is similar to the tilting flume described in the S6 MKII datasheet.

Dimensions can be modified to suit requirements.

Jacking Systems

Tilting flumes need jacks to raise and lower them. The need for stability and the size and weight of the installation make this element of crucial importance.

Various options are available, including chain drive and hydraulic lift. None, however, give the degree of repeatable accuracy achievable with screw jacks driven through shafting and gear boxes. The Armfield choice.

Long flumes need a series of jack stations carefully linked to avoid distortion of the main frame.

On larger flumes, or where exceptional degrees of slope are involved, a pivot mechanism at each station ensures a vertical aspect to the jacks at all times.

Other features include indicators for setting slope, soft "bearings" to limit noise, electric drives (optional) and detection systems permitting operation only if all jacks move together.

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Fixed Bed Flumes, Wave Tanks and Basins

Not all applications require a flume to be tilting. In many cases it is sufficient for the unit to have a fixed horizontal position. In such cases the options for construction are increased. The most flexible arrangement being a wood/composite and glass panelled knock-down form.

Wood/Composite and Glass Panelled Construction

Flumes of this type are invariably fixed bed, as the structure does not lend itself to the rigidity required for tilting. The knock-down format is particularly suited for research facilities where future projects may require flow channels of different proportions. The knock-down design provides for optimum flexibility in the assembly of the flume, inlet and outlet tanks, service pumps and pipework.
The walls are made of varnished plywood or composite materials and glass panels which are interchangeable. A special jointing compound, which remains plastic, is watertight and bonds itself to the glass or wood/composite, seals the panels which are themselves supported by mild steel channel sections. These sections are spaced at regular intervals and support the flume bed and side walls through adjustable jacking studs. It is therefore possible to level and align the flume with the utmost accuracy.

Steel Bed and Glass Wall Construction

Similar in construction to the tilting flume described at S6 Mk II, these flumes do not require the sophisticated underframe or jacking system of a tilting flow channel. Instead, they sit on simple 'A'frames, whilst the accuracy of the working section continues to be maintained at the same high levels prescribed for all other flow channels.

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Sediment Transport

Studies involving bed movement are increasingly relevant, frequently based around environmental issues. A topic notoriously difficult to study in the field lends itself to detailed study using a flow channel in the controlled environment of a laboratory.

Recirculating Sediment Systems

Frequently in experimentation there is the need for erosion and/or deposition. This requires the circulation of sediment. For this configuration a flow channel requires a recirculating loop enabling the water containing sediment in suspension to be recirculated. Armfield flow channels can be designed to incorporate such loops, the pipework being designed to ensure the sediment stays in suspension and does not settle out within the system.

Sediment is abrasive and this makes the selection of materials of particular importance. Pumps are usually lined with glass, valves are reduced to a minimum and flow metering is via electro-magnetic flow meters that do not require any components within the flow. Flow visualisation areas must be of toughened glass and stainless steel is essential on the base and in tanks.

Non-Recirculating Systems

These tend to be more complex and require that sediment be collected after discharge, either through a settling tank or hydro-cyclones.

Ancillary Hardware

These typically include sediment feeders and sediment samplers. Armfield have in-depth experience of all these options and are happy to advise on supply.

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Standard Flumes

Please click here for information regarding Armfield Standard Flumes (S6 MKII).

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Extended 2 year Warranty on all Armfield Products

DATA SHEET

PRODUCT CATEGORY:
Engineering Education