2. TUNNEL TEST - EQUIPMENT & PROCEDURES
2.1 Setting up the rotor, the wind tunnel, and the equipment
Description of the wind tunnel, rotor model, and equipments
The wind tunnel is an open suction type tunnel, as shown in Photo 1, with
a big testing area of 1.36 x 1.45m before contracting to a smaller testing
area of 0.45 x 0.45m. The tunnel is capable of generating wind speed below
4m/s at the larger section. The wind speed is controlled indirectly by
increasing or decreasing the tunnel fan rpm from a control panel. The
maximum allowable wind tunnel fan rpm was 1200. The information on rotor
model and equipment such as the tachometer and the anemometer can be found
from Report I, as both testings used the same equipment.
Photo 1: Front portion of the low speed wind tunnel with the side plastic
door opened
Positioning of rotor and wind tunnel setup
Previous measurements show that the maximum wind speed in tunnel is very
low. A simple testing confirmed that the rotor was unable to operate at
the tunnel highest speed of 3.07m/s. At this wind speed, the rotor simply
rotated slowly roughly around 1 to 2 revolution per second even when released
from 500rpm. By opening up the side plastic door of the wind tunnel, as
shown in Photo 2, the wind speed of more than half of the cross section
increased about 35% but the other half near the opening side was blocked.
The wind direction became slightly slanted as it curved into the tunnel
from the opening. Nonetheless, the current quality of wind seemed to be
better than that from large fans as the wind was still continuous and
remained very constant. Therefore, the decision to continue was taken.
Photo 2: The side opening left opened to create faster but curved wind.
Wind speed and direction around the possible test area inside the tunnel
was roughly checked using anemometer and thread to find the best position.
The rotor was positioned as shown in Photo 3 and previous Photo 2. Pieces
of tire rubber were placed between the frame of rotor and the floor of
tunnel for vibration damping purpose. 15kg of weights were placed on each
side of the frame to hold the rotor securely.
Photo 3: The position of the rotor in the wind tunnel
Measuring the wind speed with the anemometer
Pitot tube in the wind tunnel was not usable during testing because of
the wind’s deflected direction. The anemometer used in previous
fan testing was used again to measure wind speed at 3 points at about
10cm in front of the stationary rotor. The 1st point was the centre of
the swept area while the other 2 points were located on both sides of
the centre point at distance of about 2/3 times of the radius. Horizontal
markings on tunnel floor and a vertical stick with threads were used to
locate measuring points as shown in Photo 4. The anemometer was oriented
roughly to the wind speed direction by referring to the threads direction
before readings were taken.
Photo 4: The vertical stick used to locate the points for measuring wind
speeds
Tachometer setup and reading position
Tachometer was positioned so that its’ beams shoot straight to the
reflective tape as shown in Photo 5. Clips were used to continuously press
the ON button. A timer was placed nearby to display the elapsed time.
Because of the glare on the wind tunnel plastic wall and the display screen
on the tachometer, readings have to be taken from inside the tunnel. (I
sat, lean, and squeezed myself pathetically as small as possible near
the wall-floor corner on the opening side while recording down the data.
The position is shown by the pencil and notepad in previous Photo 3.).
Photo 5: The tachometer aimed to the reflective tape on the rotor in the
wind tunnel with the timer nearby
2.2 Testing procedures for inertia acceleration method
To bring the rotor the maximum rpm, the counter wind half was shielded
off with my body. To find the minimum possible starting rpm, the rotor
was decelerated using a leather rope (shown in previous Photo 3) tightened
around the rotor pulley. The minimum possible rpm without stalling was
recorded (Not repeated for lower wind speed due to limited time). The
value was slightly below 300rpm at maximum tunnel rpm of 1200.
To find the lowest possible operating wind speed or the cut in speed,
the tunnel’s fan rpm were reduced gradually from the maximum allowable
of 1200rpm until the rpm where the rotor ‘lost’ the fast rotation
(mostly over 300rpm) and decelerated to 1 to 2 revolution per second.
The maximum rotor rpm for each decrement of tunnel’s fan rpm were
recorded during this simple test. Wind speeds were recorded from the centre
of swept area. The lowest tunnel’s fan rpm where the cut in will
occur was 850rpm.
The test started by decelerating the unloaded rotor from maximum rpm
to the minimum starting rpm of 300. Then, the rpm for every 5 seconds
interval was recorded until the maximum speed was reached. The test was
repeated for wind speeds at tunnel rpm of 1200, 1100, and 1000.
2.3 Additional testing to calibrate anemometer to wind tunnel pitot tube
The wind speeds in the front (near suction part) and testing parts (before
contraction) were measured using an anemometer (I was in the wind
tunnel holding a stick with the anemometer at the end. The anemometer
was pointed to upstream). The corresponding fluid height in manometer
for wind tunnel pitot tube was recorded down. The readings were taken
until the maximum allowable tunnel fan rpm (the tunnel’s maximum
wind speed).
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