Wind Tunnel
Instruction Manual
C15
ISSUE 8
July 2010
Table of Contents
Copyright and Trademarks ... 1
General Overview ... 2
Equipment Diagrams... 3
Important Safety Information... 4
Introduction... 4
Electrical Safety... 4
Noise ... 4
Moving or Rotating Components ... 4
Fast-Moving Air Streams ... 5
Heavy Equipment ... 5
Water Borne Hazards ... 6
Description ... 7
Overview... 7
Important note on pressure measurement using the tunnel ... 7
Working Section ... 8
IFD7... 8
Static Pressure Sensor... 9
Manometers... 9 Circular Hatch... 10 Small Hatch ... 11 Roof Tappings ... 11 Fan ... 12 Flow Visualisation... 12
C15-11 Inclined Manometer Bank (optional accessory)... 13
C15-12 Electronic Manometer (optional accessory)... 15
C15-13 Lift and Drag Balance (optional accessory) ... 16
C15-14 Pitot Static Tube (optional accessory) ... 17
Table of Contents
C15-21 Pressure Wing (optional accessory) ... 18
C15- 22 Drag Models (optional accessory) ... 19
C15- 23 Pressure Cylinder (optional accessory) ... 19
C15-24 Bernoulli Apparatus (optional accessory) ... 20
C15-25 Boundary Layer Plates (optional accessory) ... 20
C15-26 Project Kit (optional accessory) ... 21
Installation... 22
Advisory... 22
Installation Process ... 22
Electrical Wiring Diagram ... 28
Operation ... 29
Operating the Software... 29
Operating the Equipment... 39
Equipment Specifications... 54
Overall Dimensions ... 54
Electrical Supply ... 54
Mains Water Supply ... 54
Connection to Drain... 54
Clearance ... 54
USB Channel Numbers ... 54
Available Accessories... 56
C15-10 Motor Rating ... 56
C15-11 Manometer... 56
C15-12 Manometer... 57
C15-13 Lift and Drag Balance ... 57
Requirements for the production of models of the student’s own design ... 57
Environmental Conditions... 57
Routine Maintenance ... 59
General... 59
Cleaning ... 59
RCD Test... 59
Fan check ... 60
Replenishing the Manometer Reservoir ... 60
Lubrication... 60
Spares ... 60
Calibration ... 60
Laboratory Teaching Exercises... 61
Index to Exercises ... 61
Introduction... 61
Nomenclature ... 61
Exercise A - Conversion of head measurement to pressure measurement... 64
Exercise B - Static pressure, dynamic pressure and total pressure... 69
Exercise C - Effect of change in cross section and application of the Bernoulli equation ... 73
Exercise D - Flow around a cylinder ... 78
Exercise E - Drag forces on bluff and streamlined bodies ... 83
Exercise F - Flow and pressure distribution around a symmetrical aerofoil at different angles of attack ... 89
Exercise G - Lift and Drag forces on a symmetrical aerofoil at different angles of attack... 95
Exercise H - Laminar and Turbulent Boundary Layer Development... 103
Exercise I - Project Work... 109
Disclaimer
This document and all the information contained within it is proprietary to Armfield Limited. This document must not be used for any purpose other than that for which it is supplied and its contents must not be reproduced, modified, adapted, published, translated or disclosed to any third party, in whole or in part, without the prior written permission of Armfield Limited.
Should you have any queries or comments, please contact the Armfield Customer Support helpdesk (Monday to Friday: 0800 – 1800 GMT). Contact details are as follows:
United Kingdom
International
(0) 1425 478781 (calls charged at local rate)
+44 (0) 1425 478781 (international rates apply)
Email: [email protected] Fax: +44 (0) 1425 470916
Copyright and Trademarks
Copyright © 2009 Armfield Limited. All rights reserved.
Any technical documentation made available by Armfield Limited is the copyright work of Armfield Limited and wholly owned by Armfield Limited.
Brands and product names mentioned in this manual may be trademarks or
General Overview
The C15-10 is a small wind tunnel designed for bench top operation, with a square, transparent working section and a variable-speed fan for wind speed control. The operating range is nominally 0 – 32 m/s with no model installed in the working section. The maximum velocity achievable will vary with the type of model installed and depends on the blockage created by the model (most of the models available for use in the tunnel are designed for use at lower velocity). The tunnel is designed with an inlet flow straightener and contraction ratio to give well developed air flow through the working section.
Wind tunnels are a useful tool for studying air flow around bodies. The available range of accessories is designed so that all the standard demonstrations of flow around bodies can be performed, including a visual indication of flow path as well as measurement of static and total pressures, lift and drag. The tunnel incorporates an Armfield IFD7 interface, which provides connection to a suitable PC. The supplied Armfield C15-304 software provides sensor output logging and fan control as well as performing any required calculations for each demonstration.
More detailed information may be found in the Description section, Operation section, Equipment Specifications section and Laboratory Teaching Exercises sections of this instruction manual.
Equipment Diagrams
Important Safety Information
Introduction
All practical work areas and laboratories should be covered by local safety regulations which must be followed at all times.
It is the responsibility of the owner to ensure that all users are made aware of relevant local regulations, and that the apparatus is operated in accordance with those regulations. If requested then Armfield can supply a typical set of standard laboratory safety rules, but these are guidelines only and should be modified as required. Supervision of users should be provided whenever appropriate. Your C15 Wind Tunnel has been designed to be safe in use when installed,
operated and maintained in accordance with the instructions in this manual. As with any piece of sophisticated equipment, dangers exist if the equipment is misused, mishandled or badly maintained.
Electrical Safety
The equipment described in this Instruction Manual operates from a mains voltage electrical supply. It must be connected to a supply of the same frequency and voltage as marked on the equipment or the mains lead. If in doubt, consult a qualified
electrician or contact Armfield.
The equipment must not be operated with any of the panels removed.
To give increased operator protection, the unit incorporates a Residual Current Device (RCD), alternatively called an Earth Leakage Circuit Breaker, as an integral part of this equipment. If through misuse or accident the equipment becomes electrically dangerous, the RCD will switch off the electrical supply and reduce the severity of any electric shock received by an operator to a level which, under normal circumstances, will not cause injury to that person.
At least once each month, check that the RCD is operating correctly by pressing the TEST button. The circuit breaker MUST trip when the button is pressed. Failure to trip means that the operator is not protected and the equipment must be checked and repaired by a competent electrician before it is used.
Noise
This equipment generates noise when running.
It is advisable to switch off the equipment before giving verbal instructions.
Ensure that all local noise regulations are followed when positioning the apparatus for use.
Depending on operator comfort, duration of operation and local noise regulations, ear defenders may be required. Noise emissions should be measured with the tunnel in its operational location.
Noise levels should be rechecked if the equipment is repositioned, as the new surroundings will absorb and reflect sound differently.
Important Safety Information
Do not remove any protective guards while the equipment is in operation.
When operating the apparatus ensure that long hair is tied back out of the way, and that clothing and jewelry cannot come into contact with any moving parts. Dangling items such as necklaces or neckties must be removed or secured so that they cannot become entangled in the equipment.
Do not touch any moving components while the apparatus is in use, or insert any item into any moving or rotating section of the equipment, unless
specifically instructed to do so in the Operational or Experimental sections of this manual.
Ensure that the apparatus is switched off and that all moving parts have come to rest before handling the equipment before changing the model in use.
All models used must be firmly secured in place, with no loose components that could become detached in use.
Fast-Moving Air Streams
This apparatus generates fast moving air streams at inlet and outlet.
Ensure that the equipment is positioned so that there are no obstructions to air entering or leaving the Wind Tunnel.
Be aware that air will be moving quickly at the inlet and outlet of the wind tunnel. There is a risk that light objects may be sucked into the inlet or blown over up to several meters from the outlet.
To avoid possible damage to eyesight, avoid looking directly into the outlet when the wind tunnel is in operation.
All loose clothing such as neckties, scarves and long hair must be securely fastened.
Ensure that the tunnel is positioned appropriately.
All models used must be firmly secured in place, with no loose components that could become detached in use.
Heavy Equipment
This apparatus is heavy.
The apparatus should be placed in a location that is sufficiently strong to support its weight, as described in the Installation section of the manual.
Use lifting tackle, where possible, to install the equipment. The equipment may be securely fastened to a pallet for lifting/carrying to the installation location using a fork-lift or similar. The equipment MUST be supported by the metal frame during lifting, NOT by the tunnel itself. Where manual lifting is necessary, two or more people may be required for safety, and all should be made aware of safe lifting techniques to avoid strained backs, crushed toes, and similar injuries.
Water Borne Hazards
The equipment described in this instruction manual involves the use of water, which under certain conditions can create a health hazard due to infection by harmful micro-organisms.
For example, the microscopic bacterium called Legionella pneumophila will feed on any scale, rust, algae or sludge in water and will breed rapidly if the temperature of water is between 20 and 45°C. Any water containing this bacterium which is sprayed or splashed creating air-borne droplets can produce a form of pneumonia called Legionnaires Disease which is potentially fatal.
Legionella is not the only harmful micro-organism which can infect water, but it serves as a useful example of the need for cleanliness.
Under the COSHH regulations, the following precautions must be observed:
Any water contained within the product must not be allowed to stagnate, ie. the water must be changed regularly.
Any rust, sludge, scale or algae on which micro-organisms can feed must be removed regularly, i.e. the equipment must be cleaned regularly.
Where practicable the water should be maintained at a temperature below 20°C. If this is not practicable then the water should be disinfected if it is safe and appropriate to do so. Note that other hazards may exist in the handling of biocides used to disinfect the water.
A scheme should be prepared for preventing or controlling the risk incorporating all of the actions listed above.
Further details on preventing infection are contained in the publication “The Control of Legionellosis including Legionnaires Disease” - Health and Safety Series booklet HS (G) 70.
Description
Where necessary, refer to the drawings in the Equipment Diagrams section.
Overview
The C15-10 is a small wind tunnel with a square working section (15) that is designed for bench top operation. Air is drawn in through the working section by a variable speed fan (10) located at the discharge end of the tunnel. A honeycomb type flow straightener (2) and a 9.4:1 contraction ratio (3) ensure well developed air flow through the working section. Accessories include an electronic manometer bank, which, together with the supplied IFD7 Electrical Console and C15-304 software, allows full electronic monitoring and recording of the measured pressures on a suitable PC (not supplied).
Important note on pressure measurement using the tunnel
To minimise turbulence inside the working section the fan is mounted at the
discharge end of the tunnel so that air is sucked through the working section. When the fan is operating the pressure inside the working section is therefore
sub-atmospheric and any static pressure measurement will be slightly below sub-atmospheric pressure.
When using the C15-11 Inclined manometer, the bottom of each tube is connected to a common water reservoir and the top of appropriate tubes are connected to the tunnel or a model inside the tunnel. At atmospheric pressure (no air flow) each manometer tube will indicate the same level at the bottom of the tube that is
coincident with the level in the water reservoir. As the air velocity increases the static pressure falls inside the tunnel and water is drawn up the relevant tubes i.e. lower pressure results in larger readings on the manometer.
The left hand manometer tube on C15-11 is connected to the static pressure tapping at the rear of the working section to provide a datum for measurements inside the tunnel. This measurement can also used for calculating the air velocity at the entrance to the working section. Any manometer tube left disconnected is open to atmosphere and therefore shows the atmospheric datum. Absolute pressures in the tunnel may be determined by relating the tunnel datum to the atmospheric datum then adding the measured barometric pressure.
Total pressure, as the sum of the static and dynamic pressures, will be higher than the static pressure and will therefore give a smaller differential between the (sub-atmospheric) reading and the outside air pressure, and thus a lower reading on the manometer than that for static pressure. For example, when using the C15-14 Pitot Static tube the static tapping will register higher on the manometer than the total pressure tapping. This is the opposite of normal convention when a Pitot Static tube is used in free air (where the total head reading would be greater than the static head reading). An illustration is provided below.
Graph of pressure differentials in the C15 wind tunnel (Not to scale)
Ignoring frictional losses the Total pressure (stagnation pressure) in the free stream will be equal to the atmospheric pressure so Total pressure measured using the optional C15-14 will be very close to the atmospheric pressure indicated in unused tubes of the manometer.
Note that when the absolute local total pressure is greater than the absolute local static pressure, the manometer reading for total pressure will be lower than the reading for static pressure.
N.B. Usually local static pressure = tunnel static pressure. Exceptions occur when the cross-sectional area at the point of measurement is modified, for example when using the C15-24 Bernoulli Apparatus (Venturi).
Pressures in the tunnel are sub-atmospheric due to the increased velocity and reduced cross-sectional area. The effect of changing velocity and area on fluid pressure is described by the Bernoulli Equation and is investigated in Exercise C.
Working Section
The working section (15) is 150 mm (6”) square and constructed from clear acrylic to give good visibility of the models in operation. The overall length of the working section is 455mm. Appropriate model / instrumentation mounting points are included in the side wall and roof of the working section. The entire base of the working section is also removable to allow the insertion of large or complex models such as the C15-24 Bernoulli Apparatus, C15-25 Boundary Layer Plate or alternative models constructed by the user.
IFD7
The C15-10 Wind Tunnel is supplied with the Armfield IFD7 Electrical Console (11) fitted, allowing the equipment to be controlled from a suitable PC (not supplied) via a USB port.
Description
Static Pressure Sensor
An electronic pressure sensor (5) mounted in a tapping through the side wall at the rear of the working section measures the static pressure inside the working section, allowing the instantaneous air velocity to be calculated and displayed on the
computer. The support plug incorporating the pressure sensor can be interchanged with the upstream blanking plug in the roof to allow measurement of the static pressure when using the optional Bernoulli Apparatus C15-24 (see Roof Tappings).
Manometers
A manometer bank is required for use with some of the models. Two options are available: a 13 tube inclined water manometer (C15-11) or a sixteen channel electronic manometer (C15-12).
C15-12 Electronic Manometer
With the C15-12 electronic manometer the readings and data logging are integrated with the wind tunnel operational software. With the C15-11 water manometer the readings can still be integrated and recorded, but need to be entered into the computer manually. Both manometers incorporate quick release connectors that allow appropriate models or instruments to be connected in seconds. For further details about the two alternative manometers refer to C15-11 Inclined Manometer
Bank (optional accessory) and C15-12 Electronic Manometer (optional accessory).
Circular Hatch
Many of the optional models are mounted through a circular opening (7), 120 mm diameter, in the front wall of the working section. These models are permanently mounted on a hatch cover to seal the opening (flush with the inside wall of the working section to avoid disturbing the flow). The hatch cover is secured by quick release clamps on the side wall of the working section allowing rapid change from one model to another.
Where necessary the hatches incorporate an angular scale allowing the model to be manually rotated to known angles.
The standard hatch cover supplied with the C15-10 Wind Tunnel incorporates a central boss with a hole, locating slot and clamping screw. This feature allows optional models such as C15-20 or C15-22 to be mounted securely in the working section when performing flow visualisation studies or when used in conjunction with the Wake survey rake (C15-15). This avoids unnecessary handling of the C15-13 Lift & Drag Balance and allows these models to be used where C15-13 is not available. A plain, clear acrylic hatch cover is supplied with the Project kit (C15-26). This can be modified as required by the user to mount alternative models.
Description
Small Hatch
A second, smaller hatch (8) behind the model mounting position allows the optional Wake Survey Rake (C15-15) to be installed downstream of the various optional models. A plain hatch cover is installed until this option is fitted.
Roof Tappings
Three tappings (6) in the roof of the working section allow the flow visualisation system (supplied with C15-10) or the Pitot Static tube (option C15-14) to be inserted. These tappings are located at the start of the working section, upstream and
downstream of the model mounting position. Each tapping incorporates a blanking plug, flush with the inside wall of the working section, that can be fitted when the tapping is not used to avoid disturbances in the working section.
Fan
Air flow through the working section is generated by a fan (10) located at the outlet end of the wind tunnel. The fan is fitted with a protective grill on the outside to prevent personnel from coming into contact with the rotating blades.
Care must be taken when installing a model to ensure that the model is secure before starting the fan. A model that is not secure could be sucked into the rotating fan blades causing damage to the model and damage to the fan.
Flow Visualisation
The working section incorporates a simple technique for flow visualisation around any of the optional models. A lightweight twine follows the flow contour around the model and shows if and where boundary layer separation (breakaway) occurs and where the flow becomes turbulent or reverses.
The twine passes through a stainless steel ‘L’ shaped tube that is mounted in a support plug that can be located in the roof of the working section at three alternative positions, i.e. the start of the working section (the usual position) and upstream and downstream of the model mounting position. The support plug incorporates an ‘O’ ring to retain the tube where it is positioned.
A simple adjustment arrangement allows the length and position of the twine to be varied. The vertical position of the twine can be varied by sliding the ‘L’ shaped tube up or down in the support plug. The horizontal position of the twine can be varied by rotating the ‘L’ shaped tube in the support plug. The length of the twine can be varied by allowing more or less twine to pass through the tube then securing the twine to the tube by sliding the ‘O’ ring over the end of the tube. Adjustment of the length is best carried out when the Wind Tunnel is operating. The end of the twine should be tied to the ’O’ ring before operating the fan so that the twine cannot accidentally enter the working section and become entangled with the fan.
Description
C15-11 Inclined Manometer Bank (optional accessory)
A bank of 13 transparent tubes inclined at 30° to measure small pressure differences (0 – 160 mm H2O) using water as the working fluid for safe operation and
convenience in use. When installed on the wind tunnel, the manometer is located inside the frame below the test section to the left hand side of the IFD7 Electrical Console.
The C15-11 manometer (12) incorporates a water reservoir with a screw operated displacer (13) to allow rapid adjustment of the datum level in the manometer. Any change in the level in one tube affects the level in all of the other tubes because they are connected to the common reservoir. After each adjustment to the model, the wind speed etc. the displacer should be screwed up or down as required to restore the tube(s) at atmospheric pressure to the original datum. All readings can then be recorded relative to a common datum.
The manometer incorporates quick release connectors on the side for rapid connection to appropriate models and instruments. The 10 way connector is
connected to tubes 1 to 10 and the two separate connectors are connected to tubes 11 and 12.
A sliding cursor is fitted to each manometer tube. These can be slid along the tubes to record the different water levels. The reading is then preserved when a change is made allowing comparison of results. Alternatively a set of readings can be
preserved when the fan is switched off. The cursors also make the calculation of differential readings easier and help to reduce parallax error. All of the cursors can be slid to the bottom or top of the tubes when not required.
Description Each bold engraved line on the backboard corresponds to 10 mm H2O, each fine line
corresponds to 2 mm H2O (the reading is magnified by a factor of x2 because the
tube is inclined at 30°).
For conversion to alternative engineering units: 1 mm H2O = 9.80665 Pascals (N/m2)
1 mm H2O = 0.001 422 334 PSI
1 mm H2O = 0.039 37 Inches H2O
As described already (see Important note on pressure measurement using the tunnel), the static pressure in the working section will be sub-atmospheric when the fan is operating. Reducing pressure will be displayed as increasing head on the inclined manometer because the tappings in the working section are connected to the top of each manometer tube and reduced pressure will suck water up the tube. Stagnation pressure in the working section will be very close to atmospheric
pressure, allowing for frictional losses, i.e. a low reading on the manometer when the fan is in operation. The relative values can be converted to absolute values if an illustration of typical pressure behaviour is required.
C15-12 Electronic Manometer (optional accessory)
An electronic console incorporating 16 differential pressure sensors, each with a range of 0-178 mm H2O. When installed on the wind tunnel, the electronic
manometer is located inside the frame below the test section to the left hand side of the IFD7 Electrical Console. The electronic manometer can be secured to the frame by transferring one of the straps from the IFD7 to the C15-12 (Two straps are fitted to the IFD7 for shipping but only one is required in normal use). The electrical supply for the manometer is obtained from the outlet socket on the front of the IFD7.
A common tapping ensures that all of the differential pressure sensors are
referenced to atmospheric pressure. Quick release connectors (7x single and 1x 10-way) allow for rapid connection to models and instruments.
The electronic manometer connects to the control PC using a second USB port on the PC, and the readings are fully integrated with the wind tunnel control software for ease of use (Use C15-12 version of the software).
As described already (see Important note on pressure measurement using the tunnel ), the stagnation pressure in the working section will be very close to atmospheric pressure, allowing for frictional losses, when the fan is in operation. To match the results from the C15-11 inclined manometer, static pressure readings below atmospheric pressure are displayed as positive values so static pressure will be greater than the corresponding total pressure readings. The relative values can be converted to absolute values if an illustration of typical pressure behaviour is required.
C15-13 Lift and Drag Balance (optional accessory)
A 2-component, electronic balance used to measure the lift and drag on appropriate models (Not used with models having multiple internal tapping points). The lift and drag models connect to the balance with a fixing pin for correct alignment. Electronic sensors are used to measure the lift and drag forces, the drag being measured directly and the lift by a reduction in the model weight. The model being tested can also be rotated on the mounting and the angle of rotation measured electronically.
The readings from the lift and drag sensors and the rotation sensor are displayed on the control software screen running on the PC, and are available for data logging. All three readings should be zeroed in the software before taking measurements as follows:
The Lift reading should be zeroed with the weight of the model resting on the
balance. The Drag reading should be zeroed with no rearward force on the balance. The rotation reading should be zeroed with the model at zero angle of attack (cursor on the body at mid position – two lines aligned).
The balance is designed to accommodate C15-20 or C15-22 but can also
accommodate alternative models manufactured by the user. A transit screw ensures that the lever arm is isolated from the load cells to prevent damage to the cells during transport or handling. It is important to clamp the lever arm at all times when the balance is not fitted in the wall of the tunnel.
Description
Note: To avoid unnecessary handling of the C15-13 Lift & Drag Balance, optional
models C15-20 and C15-22 can be mounted directly in the working section via the large circular hatch when performing flow visualisation studies or when used in conjunction with the Wake survey rake (C15-15).
C15-14 Pitot Static Tube (optional accessory)
A miniature Pitot Static tube mounted in a support plug that can be located in the roof of the working section at three alternative positions, i.e. the start of the working section and upstream and downstream of the model mounting position. The support plug incorporates an ‘O’ ring to retain the Pitot Tube where it is positioned and allows the tube to traverse over the full height of the working section to measure the velocity profile inside the working section of the tunnel.
The Pitot Static tube is constructed from two concentric stainless steel tubes. The inner tube is open at the tip and measures the Total head. The outer tube
incorporates a ring of small holes in the side that measure the static head. The overall diameter of the Pitot Static tube is 4 mm to give a stiff assembly without unduly disturbing the airflow downstream and the ‘L’ shaped arrangement, with the tip pointing into the flow, gives minimal disturbance at the point of measurement. The two flexible tubes from the Pitot Static tube incorporate a quick release connector that allows it to be connected to one of the optional manometers.
The Pitot Static is of Prandtl design and may be used with a negligible correction up to angles of yaw of at least 5 degrees.
C15-15 Wake Survey Rake (optional accessory)
The rake consists of 10 stainless steel tubes positioned vertically in a row and pointing towards the airflow. The rake is mounted downstream of the model being used via the small access hatch in the side wall of the working section. The tubes are mounted at a fixed pitch of 5mm and are connected via flexible tubing to a multi-way quick release connector to suit the C15-11 or C15-12 manometers.
When used with models such as the C15-16 Pressure Wing, readings can be taken from the pressure tappings on the model and the Wake Survey Rake without changing any settings by simply swapping the quick release connector on the appropriate manometer.
C15-20 Lift and Drag Aerofoil (optional accessory)
A plain symmetrical aerofoil to NACA 0015 profile, incorporating a mounting rod that allows it to be installed on the C15-13 Lift & Drag Balance, thus allowing the lift and drag to be measured at different angles of attack.
The aerofoil has the same section as C15-21 to allow direct comparison of lift characteristics with the pressure distribution.
A location peg on the support shaft ensures that the aerofoil is correctly positioned when fitted to the lever arm on C15-13.
To avoid unnecessary handling of the C15-13 Lift & Drag Balance, the C15-20 can be mounted directly in the working section when performing flow visualisation studies or when used in conjunction with the Wake survey rake (C15-15).
C15-21 Pressure Wing (optional accessory)
Description working section, and the angle of attack is adjustable by rotating the circular hatch. Although only instrumented on one side, the effective pressure distribution on both surfaces can be obtained by inclining the aerofoil at positive and negative angles of attack. Machined to NACA 0015 profile, the aerofoil has the same section as C15-20 to allow direct comparison of pressure distribution with the lift characteristics.
The tapping points are all flush with the surface of the aerofoil and connected via flexible tubing to a multi-way quick release connector to suit the C15-11 or C15-12 manometers.
The NACA 0015 is one of a standard series of aerofoils. The 00 indicates that the two faces are symmetrical. The 15 indicates that the airfoil has a 15% thickness to chord (width) ratio, i.e. its thickness is 15% of its chord. This ratio is fairly typical for low-speed aerofoils, and possible applications include boat rudders as well as aircraft wings.
C15- 22 Drag Models (optional accessory)
Seven different models are provided for use with the C15-13 lift and drag balance for investigations into the influence of shape on the drag forces. Five models are
supplied with a common equatorial diameter of 50mm, thus all presenting the same cross section to the airflow:
Sphere
Hemisphere, convex to airflow Hemisphere, concave to airflow Circular disk
Streamlined shape
Additionally a dimpled golf ball and plain sphere of 43mm diameter are supplied to demonstrate the difference in drag force due to the dimples. This smaller sphere can also be compared with the larger sphere to show the change in drag due to the cross sectional area.
A spare support rod is supplied for drag calibration purposes.
To avoid unnecessary handling of the C15-13 Lift & Drag Balance, the models supplied with C15-22 can be mounted directly in the working section when performing flow visualisation studies or when used in conjunction with the Wake survey rake (C15-15).
A plain cylinder, 30mm diameter, incorporating 10 equi-spaced tapping points around half of the circumference that allow the pressure distribution around the cylinder to be measured. The cylinder is mounted in the horizontal plane through the side of the working section and can be rotated through 180° to plot the pressure distribution over the whole circumference.
The tapping points are all flush with the surface of the cylinder and connected via flexible tubing to a multi-way quick release connector to suit the C15-11 or C15-12 manometers.
C15-24 Bernoulli Apparatus (optional accessory)
A Venturi profile that is installed in the working section of the tunnel via the removable floor. The Venturi incorporates 11 pressure tappings in the floor,
connected via flexible tubing to quick release connectors to suit the 11 or C15-12 manometers.
The Venturi occupies the full height of the working section and the width varies from full width at the inlet and outlet to 100 mm at the throat. It is manufactured from clear acrylic for full visualisation.
By itself the C15-24 may be used to show the variation in static pressure with change in cross section, but when used in conjunction with the Pitot Static tube (C15-14) the Bernoulli equation can be fully demonstrated.
When using C15-24, the static pressure sensor should be moved from the tapping in the rear wall to the upstream tapping in the roof of the working section to avoid errors in the static pressure measurement caused by the wall of the Venturi downstream of the rear tapping.
C15-25 Boundary Layer Plates (optional accessory)
A flat plate is mounted vertically in the working section via a removable floor panel incorporating a horizontal slot. A special flattened Pitot tube, mounted on a traversing micrometer, allows the air velocity to be measured at different distances from the surface of the plate. The plate can be moved relative to the Pitot tube to allow the velocity profile to be measured at any position between the leading edge and the trailing edge of the plate.
The special Pitot tube allows the average air velocity to be measured over a relatively small change in height. A solid rod downstream of the Pitot tip ensures that the
Description A smooth plate and artificially roughened plate are included to show the difference between the development of laminar and turbulent boundary layers. The flexible tubing from the Pitot tube incorporates a quick release connector to suit the C15-11 or C15-12 manometers.
C15-26 Project Kit (optional accessory)
The Project Kit provides a range of mountings suitable for models of the students’ own design. These mountings are made to fit the working section, so that students may concentrate on the design of the model itself. The kit also includes a selection of suitable flexible tubing for connecting tapping points to sensors, and connectors for use with the optional manometers.
Installation
Advisory
Before operating the equipment, it must be unpacked, assembled and installed as described in the steps that follow. Safe use of the equipment depends on following the correct installation procedure.
Installation Process
1. This equipment is heavy. It may be most convenient to move the equipment to its final location before unpacking it.
2. Remove all packing from the equipment. Retain all cables, thumbscrews, and other loose items (Most accessories may be unpacked after the initial
installation is complete).
3. Check all items against the Advice Note included with the equipment. If any items are missing, inform Armfield or the local agent immediately. The IFD7, blank front circular hatches and clear acrylic floor are all fitted prior to
shipping. Check that these are all present.
4. Check that the static pressure sensor is fitted to the tapping on the rear face of the working section (at the inlet end). A flexible tube from the side of this tapping allows the static tapping to be connected to a C15-11 or C15-12 manometer (when supplied).
5. All items are inspected before dispatch. Check all items for damage received in transit, and inform Armfield or the local agent of any damage or breakages. 6. The C15-10 should be placed on a firm, level surface that is sufficiently strong
Installation 7. With a spirit level placed along the metal frame at the base of the equipment,
adjust the feet until the tunnel is horizontal.
8. Check the fan is free from obstructions and that the blades can rotate freely. Check that the fixings on the guard are securely fastened.
9. Check the honeycomb insert in the tunnel inlet to ensure all holes are clear of obstructions.
If using the C15-11, this should be fixed to the frame, to the left of the IFD7, using the thumb nuts supplied. The flexible tube from the static should be connected to the top of the left hand manometer tube.
11. For C15-12
If using the C15-12, this should be located to the left of the IFD7. The C15-12 can be secured to the frame using one of the straps from the IFD7 (Two straps are fitted to IFD7 to ensure safe transit).
12. Check that the cables from the fan motor and sensors on the tunnel are securely connected to the sockets front of the IFD7.
Installation 13. Install the C15-304 software on a suitable PC then restart the PC. Connect
the IFD7 to the PC using the USB cable supplied. If using the C15-12, connect this to one USB port on the PC before connecting the IFD7 to a second USB port. Check that the red and green indicator lights on the IFD7 (and the C15-12 if used) are illuminated. The PC should automatically detect the connected USB device(s) and install the correct driver(s).
14. Run the C15-304 software. Two versions of the software are installed, one version for use with the C15-11 Inclined Manometer Bank and the other version for use with the C15-12 Electronic Manometer.
15. For version C15-B only
This version of the C15 Wind Tunnel is supplied with a loose transformer to step-up the local 115/120V electrical supply to 220/240V to suit the equipment. The transformer should be located adjacent to a 115/120V electrical outlet socket in the laboratory.
Connect the mains lead from the rear of the IFD7 to the 220V outlet socket on the front of the transformer.
Connect the transformer to the 115/120V mains outlet socket in the laboratory then switch on the electrical supply.
Go to step 17.
16. For versions C15-A and C15-G
Connect the IFD7 to a suitable mains electricity supply.
17. If using C15-12, this should be connected to the 240V outlet socket on the IFD7 using the mains lead supplied with C15-12.
18. Switch on the IFD7. A warning message will indicate if the IFD7 needs configuring to suit the equipment. Refer to the IFD7 Instruction Manual for further details.
The fan should NOT start at this stage. If it does so then suspect an electrical fault; shut down the equipment and contact Armfield or your local agent for assistance.
Installation
19. Run the appropriate C15-304 software (C15-11 if using the inclined
manometer bank, C15-12 if using the electronic manometer) and select the Project Work exercise. Check that ‘IFD: OK’ is indicated in the bottom right of the software window.
20. In the software, select the ‘Fan On’ button on the mimic diagram. Check that the ‘Watchdog Enabled’ indicator on the mimic diagram is activated.
21. Use the arrow keys beside the fan speed box to gradually increase the fan speed. Check that the fan begins to operate. Check that the indicated static pressure reading increases. Check that a velocity reading is indicated.
22. Set the fan speed back to zero. Select ‘Fan On’ to set the IFD7 to standby. Switch off the power switch on the front of the IFD7. Exit the software.
The basic operation of the C15 Wind Tunnel has been confirmed. Refer to the Operation section for further information.
Electrical Wiring Diagram
Click on the relevant link to invoke the Wiring Diagram: Wiring Diagram ACM31434
Printed Versions of this Instruction Manual
Please note, all wiring diagrams are appended at the rear of this manual
Operation
Where necessary, refer to the drawings in the Equipment Diagrams section.
Operating the Software
Note: The diagrams in this section are included as typical examples and may not
relate specifically to the individual product described in this instruction manual. The Armfield Software is a powerful Educational and Data Logging tool with a wide range of features. Some of the major features are highlighted below, to assist users, but full details on the software and how to use it are provided in the presentations and Help text incorporated in the Software. Help on Using the Software or Using the Equipment is available by clicking the appropriate topic in the Help drop-down menu from the upper toolbar when operating the software as shown:
Before operating the software ensure that the equipment has been connected to the IFD7 Interface and the IFD7 has been connected to a suitable PC using a USB lead. For further information on these actions refer to the Operational manual.
Load the software. If multiple experiments are available then a menu will be
displayed listing the options. Wait for the presentation screen to open fully as shown:
Before proceeding to operate the software ensure that IFD: OK is displayed at the bottom of the screen. If IFD:ERROR is displayed check the USB connection between the IFD7 and the PC and confirm that the red and green LED’s are both illuminated. If the problem persists then check that the driver is installed correctly (refer to the Operational manual).
A warning message will be displayed if the IFD7 has not been configured to match the product in use. Refer to the Operational manual for further information if the IFD7 needs to be configured.
Presentation Screen - Basics and Navigation
As stated above, the software starts with the Presentation Screen displayed. The user is met by a simple presentation which gives them an overview of the capabilities of the equipment and software and explains in simple terms how to navigate around the software and summarizes the major facilities complete with direct links to detailed context sensitive ‘help’ texts.
To view the presentations click Next or click the required topic in the left hand pane as appropriate. Click More while displaying any of the topics to display a Help index related to that topic.
To return to the Presentation screen at any time click the View Presentation icon from the main tool bar or click Presentation from the dropdown menu as shown:
For more detailed information about the presentations refer to the Help available via the upper toolbar when operating the software.
Toolbar
A toolbar is displayed at the top of the screen at all times, so users can jump immediately to the facility they require, as shown:
The upper menu expands as a dropdown menu when the cursor is placed over a name.
The lower row of icons (standard for all Armfield Software) allows a particular function to be selected. To aid recognition, pop-up text names appear when the cursor is placed over the icon.
Mimic Diagram
The Mimic Diagram is the most commonly used screen and gives a pictorial
representation of the equipment, with continuously updated display boxes for all the various sensor readings, calculated variables etc. directly in engineering units.
Operation
To view the Mimic Diagram click the View Diagram icon from the main tool bar or click Diagram from the View drop-down menu as shown:
A Mimic diagram is displayed, similar to the diagram as shown:
The details in the diagram will vary depending on the experiment chosen if multiple experiments are available.
In addition to measured variables such as Temperature, Pressure and Flowrate (from a direct reading flowmeter), calculated data such as Motor Torque, Motor Speed and Discharge / Volume flowrate (from pressure drop across an orifice plate) are
continuously displayed in data boxes with a white background. These are automatically updated and cannot be changed by the user.
Manual data input boxes with a coloured background allow constants such as Orifice Cd and Atmospheric Pressure to be changed by over-typing the default value, if required.
an inherent characteristic of pressure sensors. Pressing the Zero button just before starting a set of readings resets the zero measurement and allows accurate pressure measurements to be taken referenced to atmospheric pressure. This action must be carried out before the motor is switched on otherwise the pressure readings will be offset.
The mimic diagram associated with some products includes the facility to select different experiments or different accessories, usually on the left hand side of the screen, as shown:
Clicking on the appropriate accessory or exercise will change the associated mimic diagram, table, graphs etc to suit the exercise being performed.
Control Facilities in the Mimic Diagram
A Power On button allows the motor to be switched off or on as required. The button always defaults to off at startup. Clicking this button switches the power on (1) and off (0) alternately.
A box marked Motor Setting allows the speed of the motor to be varied from 0 to 100% either stepwise, by typing in values, or using the up / down arrows as
appropriate. It is usual to operate the equipment with the motor initially set to 100%, then reduce the setting as required to investigate the effect of reduced speed on performance of the equipment.
When the software and hardware are functioning correctly together, the green LED marked Watchdog Enabled will alternate On and Off. If the Watchdog stops alternating then this indicates a loss of communication between the hardware and software that must be investigated.
Details on the operation of any automatic PID Control loops in the software are included later in this section.
Operation
Data Logging Facilities in the Mimic Diagram
There are two types of sampling available in the software, namely Automatic or Manual. In Automatic logging, samples are taken regularly at a preset but variable interval. In Manual logging, a single set of samples is taken only when requested by the operator (useful when conditions have to be changed and the equipment allowed to stabilize at a new condition before taking a set of readings).
The type of logging will default to manual or automatic logging as appropriate to the type of product being operated.
Manual logging is selected when obtaining performance data from a machine where conditions need to stabilize after changing appropriate settings. To record a set of set of data values from each of the measurement sensors click the icon from the main toolbar. One set of data will be recorded each time the icon is clicked. Automatic logging is selected when transients need to be recorded so that they can be plotted against time. Click the icon from the toolbar to start recording, click the icon from the toolbar to stop recording.
The type of logging can be configured by clicking Configure in the Sample drop-down menu from the upper toolbar as shown:
In addition to the choice of Manual or Automatic sampling, the parameters for
Automatic sampling can also be set. Namely, the time interval between samples can be set to the required number of minutes or seconds. Continuous sampling can be selected, with no time limit or sampling for a fixed duration can be set to the required number of hours, minutes or seconds as shown:
Tabular Display
To view the Table screen click the View Table icon from the main tool bar or click Table from the View dropdown menu as shown:
The data is displayed in a tabular format, similar to the screen as shown:
As the data is sampled, it is stored in spreadsheet format, updated each time the data is sampled. The table also contains columns for the calculated values. New sheets can be added to the spreadsheet for different data runs by clicking the
icon from the main toolbar. Sheets can be renamed by double clicking on the sheet name at the bottom left corner of the screen (initially Run 1, Run 2 etc) then entering the required name.
For more detailed information about Data Logging and changing the settings within the software refer to the Help available via the upper toolbar when operating the
Operation
Graphical Display
When several samples have been recorded, they can be viewed in graphical format. To view the data in Graphical format click the View graph icon from the main tool bar or click Graph from the View drop-down menu as shown:
The results are displayed in a graphical format as shown:
(The actual graph displayed will depend on the product selected and the exercise that is being conducted, the data that has been logged and the parameter(s) that has been selected).
Powerful and flexible graph plotting tools are available in the software, allowing the user full choice over what is displayed, including dual y axes, points or lines,
displaying data from different runs, etc. Formatting and scaling is done automatically by default, but can be changed manually if required.
To change the data displayed on the Graph click Graph Data from the Format dropdown menu as shown:
The available parameters (Series of data) are displayed in the left hand pane as shown:
Two axes are available for plotting, allowing series with different scaling to be presented on the same x axis.
To select a series for plotting, click the appropriate series in the left pane so that it is highlighted then click the appropriate right-facing arrow to move the series into one of the windows in the right hand pane. Multiple series with the same scaling can be plotted simultaneously by moving them all into the same window in the right pane. To remove a series from the graph, click the appropriate series in the right pane so that it is highlighted then click the appropriate left-facing arrow to move the series into the left pane.
The X-Axis Content is chosen by default to suit the exercise. The content can be changed if appropriate by opening the drop down menu at the top of the window. The format of the graphs, scaling of the axes etc. can be changed if required by clicking Graph in the Format drop-down menu as shown:
Operation
For more detailed information about changing these settings refer to the Help available via the upper toolbar when operating the software.
PID Control
Where appropriate, the software associated with some products will include a single or multiple PID control loops whereby a function on the product can be manually or automatically controlled using the PC by measuring an appropriate variable and varying a function such as a heater power or pump speed.
The PID loop can be accessed by clicking the box labelled PID or Control depending on the particular software:
A PID screen is then displayed as shown:
The Mode of operation always defaults to Manual control and 0% output when the software is loaded to ensure safe operation of the equipment. If appropriate, the operator can retain manual operation and simply vary the value from 0 to 100% in the
Manual Output box, then clicking Apply.
Alternatively, the PID loop can be changed to Automatic operation by clicking the
Automatic button. If any of the PID settings need to be changed from the default
values then these should be adjusted individually before clicking the Apply button. The controller can be restored to manual operation at any time by clicking the
Manual button. The value in the Manual Output box can be changed as required
before clicking the Apply button.
Settings associated with Automatic Operation such as the Setpoint, Proportional
Band, Integral Time, Derivative Time and Cycle Time (if appropriate) can be
changed by the operator as required before clicking the Apply button.
Clicking Calculations displays the calculations associated with the PID loop to aid understanding and optimization of the loop when changing settings as shown:
Operation
Clicking Settings returns the screen to the PID settings.
Clicking OK closes the PID screen but leaves the loop running in the background. In some instances the Process Variable, Control variable and Control Action can be varied to suit different exercises, however, in most instances these boxes are locked to suit a particular exercise. Where the variables can be changed the options available can be selected via a drop-down menu.
Advanced Features
The software incorporates advanced features such as the facility to recalibrate the sensor inputs from within the software without resorting to electrical adjustments of the hardware. For more detailed information about these advanced functions within the software refer to the Help available via the upper toolbar when operating the software.
Operating the Equipment
Preparation of the tunnel for use
Before switching on the Wind Tunnel: Ensure that the required model and/or measuring instrument has been securely installed in the working section
Any adjustable or removable features must be fastened or clamped to prevent movement.
Ensure that all appropriate hatches, covers etc have been secured.
Ensure that nothing is obstructing the inlet or the outlet of the wind tunnel.
Ensure that the IFD7 Electrical Console has been connected to the USB port on the control PC.
Note: When using the optional C15-12 Electronic Manometer ensure that the
USB lead from the C15-12 is connected to the PC followed by the USB lead from the IFD7 to ensure correct operation.
Switch on the RCD at the rear of the IFD7 Electrical Console.
Switch on the mains power switch at the front of the IFD7 Electrical Console.
Load the appropriate exercise from the C15 software. Note: Different software should be loaded to suit operation with either C15-11 or C15-12. If not using a manometer supplied by Armfield then the C15-11 software should be loaded.
Where the exercise offers a choice of multiple models, select the correct model.
Starting up
Switch on power to the fan by clicking the ‘Fan On’ button in the software. The button will indicate ‘1’ when the fan is ready for use.
Gradually increase the fan speed using the software control box until the required air velocity is indicated. Always start at low velocity then gradually increase the velocity, checking readings on the manometers, lift/drag balance etc. to ensure that everything is assembled and connected correctly. The setting may be adjusted using the up and down arrow buttons, or a value may be typed directly into the box using the
keyboard.
Note: When using the C15-11 Inclined Manometer it is important to ensure that the
water level in any of the tubes does not reach the top manifold as water will be drawn into the flexible tubing. This will not present a safety hazard but water in the tubing will affect the accuracy of subsequent readings on the manometer. If water does enter the flexible tubing it will be necessary to disconnect the tubing from the quick release connector(s) on the manometer and blow through the flexible tubing to remove the blockage. This problem can easily be avoided by gradually increasing the speed of the fan while watching the readings on the manometer.
Adjusting the air velocity
The air velocity is always adjusted from the software by altering the fan speed. Fan speed is set as a percentage of the maximum speed, between 0% and 100%. The corresponding static head in the tunnel (given as the differential head between the tunnel and atmosphere) and air velocity (in meters per second) are then displayed on the software mimic diagram.
Check that the correct exercise is loaded and that the ‘Fan On’ button has been selected to indicate ‘1’ (power supply on). Wind speed in the test section can then be adjusted by clicking on the raise or lower arrows until the required speed is indicated, or a value may be typed directly into the fan speed box.
When making adjustments it will take a few moments for the fan speed to settle due to the inertia of the fan impeller, so allow it to stabilize before checking the resulting air velocity. Continue to make small adjustments to the fan setting until the required air velocity is achieved.
Operation in the working section will change. Operation at large angle of attack will severely reduce the air velocity through the tunnel. If constant air velocity is required at different model settings then the fan speed can be adjusted after making changes to the model, starting at the maximum speed available when the model is causing the maximum blockage.
Measuring the air velocity using the PC
The instantaneous average air velocity in the test section is indicated on the PC when viewing the diagram. The air velocity is indicated in units of m/s and is calculated from the static pressure measured at the tunnel wall.
Note: Before the tunnel is used for quantitative results it will be necessary to check
the accuracy of this indicator since no account is taken of the velocity profile across the working section. The calibration may also be used as a student exercise. Sensor calibration is described in the software Help Text.
Measuring the air velocity using the inclined manometer bank
Tube 1 indicates static head at the start of the working section.Tubes 11 & 12 indicate atmospheric head when not connected to a model or instrument.
Velocity = √(2 *ρmanometer * 9.81 * Head differential / ρair) m/s
Where Head differential = Δh = difference between static head and atmospheric head (in meters)
ρmanometer and ρair are both temperature-dependant and thus a reading for ambient
temperature is required for accuracy. The densities are then automatically calculated by the software, although they may also be determined from standard reference tables if desired.
If a quick, approximate air velocity is required for some reason then values of 1000 kg/m³ for water and 1 kg/m³ for air may be sufficient, i.e. V ≈ 140 √Δh
Installing models and sensors via the large circular hatch
Before removing or installing a model or instrument, ensure that the air velocity is zero and the fan has stopped rotating.
If a model is already in position, the flexible tubing from the model should be disconnected from the quick-release connector(s) on the manometer before the hatch is removed. On models of the student’s own design, tappings should be disconnected at whichever position is appropriate to the design.
The hatch is secured with two swinging latches. Support any model or cover in position, and loosen but do not completely remove the two thumb nuts securing the latches. Swing the latches aside, and withdraw the hatch and any attached model horizontally until hatch and model are both clear of the working section side. Insert the new model horizontally through the circular opening, taking care not to damage the model, the working section, or any model already in position within the working section. Fit the circular hatch on which the model is fitted into the hole, and support the model in place while swinging the latches into place to secure it and tightening the thumb nuts by hand.
Connect the flexible tubing from the model or instrument to the required manometer via the quick release connector(s).
If no hatch-mounted model or sensor is to be used, the basic blank hatch cover should be fitted in the same way as described for fitting a model.
Installing models via the removable floor
Before removing or installing a model or instrument, ensure that the air velocity is zero and the fan has stopped rotating.
If a model is already in position, the flexible tubing from the model should be
disconnected from the quick-release connector(s) on the manometer before the floor is removed. On models of the student’s own design, tappings should be
disconnected at whichever position is appropriate to the design.
The floor is held in position using eight thumbnuts. Remove all but two opposing corner nuts and place the nuts in a safe place. Support the floor securely before removing the final two nuts then lower the floor until the model is clear of the working section sides.
Lift the new model upwards into position, and support it while securing it in position with two nuts placed at opposite corners. Replace the other six thumb nuts,
tightening them by hand.
Connect the flexible tubing from the model or instrument to the required manometer via the quick release connector(s).
If no floor-mounted model is to be used, the basic blank floor should be fitted in the same way as described for fitting a model.
Installing the flow visualisation tube or Pitot Static tube
The procedure for inserting the flow visualisation system and the Pitot tube is
identical. However, the flow visualisation tube is usually fitted at the far upstream end of the working section while the Pitot tube is more commonly fitted centrally or
downstream within the within the working section (depending on the model used). The installation positions are fitted with blanking plugs when not in use. Loosen but do not remove the screw securing the appropriate blanking plug. Then remove the blanking plug and put in a safe place (it is not recommended that plugs are left on top of the wind tunnel, as vibration may cause them to travel).
Insert the short arm of the ‘L’ section tube into the tapping hole then carefully pass the tube through the hole until the long arm of the ‘L’ is upright within the tapping. Lower the tube until the support plug is snugly fitted into the tapping. Tighten the screw to secure the support plug.
After fitting the optional Pitot tube (C15-14), the two flexible tubes should be
connected to the quick-release fittings on the manometer (see Using the C15-14 Pitot Static Tube (requires C15-11 or C15-12) for more detail).
Using the flow visualisation system
The flow visualisation system consists of a height- and angle-adjustable tube which supports a long thread. The thread is light enough to be lifted easily by the air flow,
Operation
Vertical movement
The vertical position of the support tube is adjusted by loosening the screw in the roof tapping, carefully raising or lowering the tube within the tapping, and securing the tube in the new position by re-tightening the screw. The screw should only be tightened sufficiently to hold the tube in position. Over-tightening can damage the tube.
Horizontal movement
The tube is L-shaped, and the horizontal position of the thread may therefore be adjusted by rotating the support tube within the tapping so that the short length of the ‘L’ brings the thread across to one side or the other. Loosen the tapping screw before rotating the tube, and tighten the screw afterwards.
Adjusting length of thread
The length of thread can be adjusted to obtain the best visualisation (for example to demonstrate wake turbulence). Length can often be best adjusted during tunnel operation, and it is safe to make adjustments while the tunnel is in operation.
The thread is secured with a rubber ‘O’-ring around the top of the tube. Slide this ring up and off the tube, then shorten the thread by pulling the external end upwards through the tube, or lengthen it by feeding more thread into the tube. When the thread length is correct gently push the ‘O’-ring back onto the end of the tube to secure the thread at the required length.
Note: The end of the thread should be tied to the ‘O’-ring at all times so that
the thread cannot accidentally enter the tunnel and wrap around the rotating fan.
Using the C15-11 Inclined Manometer Bank
Connecting the equipment
Models or instruments can be connected to the manometer using the 10-way connector or two 1-way connectors that are located on the left hand side of the manometer.
The 10-way connector
The 10-way connector socket has tubes labelled 1 to 10. These correspond to the similarly-labelled tubes on the C15-11 or the labelled boxes on the software mimic diagram if connecting via the electronic manometer.
When using the 10-way connector ensure that the red clip on top of the fixed body is set to OPEN (left) before inserting the plug.
With the notch uppermost, push the plug in straight and horizontally (without twisting) until the two parts mate.
Operation
Before removing the plug ensure that the red clip is set to OPEN then pull the plug out horizontally without twisting.
The 1-way connectors
The 1-way connectors are used with accessories such as the C15-14 Pitot static tube. The two tubes connect to the single-way connectors labelled A and B.
Note that the 10-way or 1-way quick release connections can be changed while the wind tunnel is operating allowing different readings to be taken without changing the configuration of the model. For example, the pressure distribution on the surface of the aerofoil (C15-21) can be displayed on the manometer, followed by the pressure distribution from the Wake Survey Rake (C15-15) without changing the air velocity, or angle of attack.
Priming
Priming is only required with the C15-11 inclined manometer bank (Other sensors do not require the use of water). The manometer should be properly primed before use, as trapped air bubbles will affect the accuracy of the results.
Adjusting levels
A water reservoir with a screw operated displacer allows rapid adjustment of the datum level in the manometer tubes. Any change in the level in one tube affects the level in all of the other tubes because they are connected to a common reservoir. After each adjustment to the model, the wind speed etc. the displacer should be screwed up or down as required to restore the tube(s) at atmospheric pressure to the original datum. All readings can then be recorded relative to a common datum. Adjustment of the datum level does not affect the differentials between the various tubes i.e. the level in all tubes rises or falls by the same amount when the displacer is adjusted. Note that the water level will stop changing when the displacer becomes fully submerged.
Using cursors
Each manometer tube is fitted with an adjustable cursor ring which may be
positioned anywhere along the length of the tube. These are close-fitting, so that they will remain in position unless deliberately moved. The cursors should be moved either to the top of the bottom of each column when not in use, to allow maximum visibility of the columns.