The
MKII wind tunnel assembly, with the BE1
test model in the visualization chamber.
Not
directly connected with the generating history of Herstmonceux
Museum, though designed and constructed in the workshop garage, in
Lime Park, as a
way to visualize and measure the efficiency of a vehicle shape, in the
ability to pass through air, with the least resistance to
movement.
This
was the second compact re-circulating wind tunnel to be built in this
location. Designed to be a desktop machine, it is that small.
Strain gauges provided measurement of drag, lift and down-force. A
turn table was incorporated so vehicle models could be tested in side wind conditions. Air temperature and wind speed were also monitored and smoke could be trailed over models to visualize airflow, to highlight problem areas. This
instrument measured just 60" x 40" x 15". Being a closed circuit design it was not unbearably noisy in operation.
A wind tunnel is a complex piece of engineering. The
Wright Brothers were the first inventors to use such a tool to compile lift and drag tables for various wing shapes. It is much more difficult to design a balance to measure lift and down-force on each wheel of a vehicle. When working at such a small scale, accuracy of measurement is essential. Fortunately, electronics come to the rescue, with compensated amplifiers providing multiplication of movement up to a thousand.
Some
of the wind tunnel models on display at Herstmonceux Museum, the larger
ones for use in the MKII measuring instrument were 1:24 scale. The
smaller models were 1:50 scale. These were hand carved in wood, then
painted to as near as possible present a surface finish representative
of a full size vehicle. The rough grain of wood, would not have worked
so well. These models were carved in the Lime Park workshops.
A wind tunnel is a research tool developed to assist with studying the effects of air moving over or around solid objects. The most famous early experimenters to build a wind tunnel were the Wright
Brothers, Orvill and Wilbur.
Air is blown or sucked through a duct equipped with a viewing port and instrumentation where models or geometrical shapes are mounted for study. Various techniques are then used to study the actual airflow around the geometry and compare it with theoretical results, which must also take into account the Reynolds number and Mach number for the regime of operation. For example:
*Threads can be attached to the surface of study objects to detect flow direction and relative speed of air flow.
*Dye or smoke can be injected upstream into the air-stream and the streamlines that dye particles follow photographed as the experiment proceeds.
*Probes consisting of a Pitot tube can be inserted at specific points in the air flow to measure static and dynamic air pressure.
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A key component of any wind tunnel is the fan assembly. A fan should be able to generate high wind speeds, sufficient for the vehicles being tested.
Take a look at the propeller and motor to the left. A 1hp motor is mounted on eight springs to reduce vibration, rubber damped. The whole fan module is then positioned on rubber mounts, which in turn channel vibration through a weighted plywood frame. The net effect is to pass the vibration through materials with different natural frequencies, so acting as a vibration filter, much like coils and capacitors are used to filter out unwanted frequencies in Hi Fi speaker systems. Lead weights are also employed to give mass to the mild steel base frame unit. |
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Air temperature and wind speed were also monitored and smoke could be trailed over models to visualize airflow, to highlight problem areas. This tunnel could fit comfortably on an office desk. It measured just 60" x 40" x 15". Being a closed circuit design it was not unbearably noisy in operation.
The plexiglas chamber provided superb all round visibility, which is so important.
Strain gauges provided measurement of drag, lift and down-force. A rotating table was incorporated so that vehicle models could be tested in side wind conditions.
It is much more difficult to design a balance to measure lift and down-force on each wheel of a vehicle. When working at such a small scale, accuracy of measurement is essential.
Fortunately, electronics come to the rescue, with compensated amplifiers providing multiplication of movement (lift/downforce) up to ten thousand. |
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Electrical
signals, as variable voltages, are amplified and sent to
moving-coil, needle instruments in a purpose built instrument
console.
These
gauges measure micro amperes, to provide a visual indicator of
how a vehicle is performing in the wind tunnel. it is possible
to see attitude changes from lift and ground effect. Apart from
measuring simple drag. |
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The
Power Supply Unit (PSU) shows the current and operating voltage
of the main fan motor. The speed of the fan motor may be varied.
There
is also an hours run meter and temperature gauge.
The build of this wind tunnel took approximately
3 months from start to conclusion, at a cost of around £6,000 in 1988.
A bargain research tool. |
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Five
RS strain gauge amplifiers gave separate channels of information to provide a range of measurements to include
overall drag, + lift and down-force for each wheel.
Each amplifier is fed information from a
(Wheatstone) bridge of four foil resistors bonded to each element of the balance, two on each side.
The balance comprises of five elements, consequently, quite a few (20) strain gauges
were needed, and some patience during the epoxy bonding and positioning. The marking out must be exceptionally accurate for consistent results.
The components used in the making of this tunnel, were
quite expensive if you are on a small budget, but more importantly, with suppliers such as Radio Spares (RS) they are at least are widely available to
professional scientists and amateur enthusiasts. |
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Here is
a close up of the wiring of one of the five steel elements against which
the slight bend, fractionally stretched one side of the plate (increasing resistance) and compressed (lowered resistance) the other side of the
plate, alters resistance. The sensitivity (voltage) multiplication effect of such a bridge is well known.
The completed assembly is coated in silicone for environmental protection. |
WIND TUNNEL HISTORY
English military engineer Benjamin Robins (1707–1751) invented a whirling arm apparatus to determine drag. The Englishmen Wenham and Browning did air flow experiments in a wind tunnel in 1871.
The Wright Brothers, working with Octave Chanute invented and built a simple wind tunnel in 1901 to study the effects of airflow over various shapes while developing their revolutionary Wright Flyer. The Wright wind tunnel was used more recently to test modern low-speed fliers, such as the human-powered "Albatross".
Subsequent use of wind tunnels proliferated as the science of aerodynamics and discipline of aeronautical engineering were established as air travel and power were developed.
Wind tunnels were often limited in the volume and speed of airflow which could be delivered.
The wind tunnel used by German scientists at Peenemünde prior and during
WWII is an interesting example of the difficulties associated with extending the useful range of large wind tunnels.
It used some large natural caves which were increased in size by excavation and then sealed to store large volumes of air which could then be routed through the wind tunnels. This innovative approach allowed lab research in high speed regimes and greatly accelerated the rate of advance of Germany's aeronautical engineering efforts.
Later research into airflows near or above the speed of sound used a related approach. Metal pressure chambers were used to store high pressure air which was then accelerated through a nozzle designed to provide supersonic flow. The observation or instrumentation chamber was then placed at the proper location in the throat or nozzle for the desired airspeed.
Computational fluid dynamics has augmented, and is starting to replace, the use of wind tunnels. For example, the experimental rocket plane SpaceShipOne was designed without any use of wind tunnels. (However, on one test flight threads were attached to the surface of the wings, performing a wind tunnel type of test during an actual flight in order to refine the computational model.)
An area that is still much too complex for the use of Computational fluid dynamics is determining the effects of flow around buildings and bridges. Boundary layer wind tunnels are the state of the art method to test such structures. These wind tunnels are also used to simulate and measure wind characteristics at the pedestrian level and exhaust gas dispersion patterns for laboratories and other emitting sources.
Wind tunnel tests in a boundary layer wind tunnel allow for the natural drag of the earth's surface to be simulated. For accuracy, it is important to simulate the mean wind speed profile and turbulence effects within the atmospheric boundary layer. Most codes and standards recognize that wind tunnel testing can produce reliable information for designers, especially when their projects are in complex terrain or on exposed sites.
Alongside,
the world's smallest water basin, the Museum is home to some interesting
technological exhibits, many world record contenders.
There are
several innovative vehicles and vessels on permanent display at
Herstmonceux Museum, including:
1.
Art
Gallery - Collection of paintings, pictures, graphics, sculptures,
wooden carvings & exotic glassware
2.
Archives - Historic documents library, patents, trademarks,
copyright, films, catalogued legal papers & letters
3. An
Edwardian ice well, throwback to the days before refrigeration
4.
A large underground (condensation/cooling) and water storage chamber for
ice making
5. The world's smallest water
basin, test tank for model boats
6.
World's smallest
wind tunnel, vehicle drag measuring instrument using electronic
strain-gauges
7.
Three
PV boat models,
Navigator, SWATH & 2 cats + route map prior to Swiss PlanetSolar
8.
Seavax, the ocean cleanup
proof of concept prototype from 2016
9.
AmphiMax, radio controlled (working) beach launching & recovery
vehicle for SeaVax
10.
Anthony the
most dangerous giant
Australian bulldog ant, 300 times normal size
11.
EV - FCEV refueling station
model in 1:20 scale
12. The only working
(fully functional) water well in Herstmonceux village
13.
The fountain of youth, supplied from natural well water
drawn on site
14.
Second World War, 'Anderson Inspired,' bomb proof shelter constructed by Major Charles de Roemer
15.
City
sports FCEV-BEV, hydrogen gull wing proof of concept DC50 electric car
16.
Land speed record car: Bluebird-Electric BE1 (original 1st) with battery
cartridge exchange
17.
Land speed record car: Bluebird-Electric BE2 (original 2nd) with cartridge
exchange
18.
A complete mummified squirrel, found when re-roofing the Museum June
2017
19.
A fully operational, and restored VW Kombi van dating from 1978
(historic vehicle)
20.
BMW i3, battery electric vehicle hybrid, with onboard generator range
extender
21. Solar panel, sun tracking system,
with battery storage
22.
A hornet's nest found on site & preserved in 2016 (reported as
[Asian] invasive species, to be safe)
23.
Three sewing machines, including an antique Singer and a Brother
industrial.
24. Adventure climbing frames for children (back to nature)
Swiss Family Robinson
