Transcript Paper Anemometer

Paper Anemometer
Team Taiwan
Official Description
• Paper Anemometer
• When thin strips of paper are placed in an air
flow, a noise may be heard.
• Investigate how the velocity of the air flow can
be deduced from this noise?
Problem Analysis
• Two qualities of sound may be considered:
– Frequency
– Strength
Decibel Sensor
Microphone
Experimental Setup
Experimental Setup
Voltage Regulator
Metal Wire
Wind Blower
Experimental Setup
4 cm
Spaced Double
20 cm
3.3 cm
Merged Double
Experiment
Wind velocity is adjusted with a voltage
regulator, the input voltage and its
corresponding wind velocity is measured.
Noise made by the paper is measured in
decibels and recorded by a microphone.
Experiment: Frequency
Chart 1.The frequency spectrum of the noise made by the flapping
paper
Experiment: Frequency
• No specific frequency is seen in the frequency
spectrum of the noise
• Therefore, we will try to use the intensity of
the noise to estimate the velocity of the wind
Theory
• The sound intensity of a vortex interacting
with a surface is proportional to the sixth
power of the flow velocity
Source: Powell, Alan, Theory of Vortex Sound, The Journal of the Acoustical
Society of America, January 1964
Experiment: Intensity
90
Optimal Range
89
88
Decibels
87
86
10.7 m/s
85
84
83
82
0
10
20
30
40
50
60
Paper Length (cm)
Chart 1.Finding the optimum paper length for experiment
Experiment: Intensity
95
Decibels
90
6cm
9cm
12cm
15cm
85
80
75
6.5
7.5
8.5
9.5
10.5
11.5
Wind Velocity (m/s)
Chart 3.The relationship between flow velocity and decibels measured
when using different lengths of paper
Experiment: Intensity
95
Decibels
90
85
Spaced
Double
80
Merged
Double
75
Single
70
5
7
9
11
13
Wind Velocity (m/s)
Chart 4.The relationship between flow velocity and decibels measured
when using different arrangements of 15 cm paper strips.
Matching with Theory
• According to the theory, the intensity of the
noise is proportional to the sixth power of the
wind velocity.
• We will use v 
experimental data
6
k  I to fit our
Matching with Theory
13
Wind Velocity (m/s)
12
6cm
6 Predicted
11
9cm
10
9 Predicted
12cm
9
12 Predicted
8
15cm
15 Predicted
7
6
75
80
85
Decibels
90
95
Matching with Theory
Wind Velocity (m/s)
12
11
10
Double 15
Double 15 Predicted
9
Merged 15
Merged 15 Predicted
8
15cm
7
15 Predicted
6
75
80
85
90
Decibels
• Experimental results matches well with theory
• Deviations seen more often at lower wind velocities
Matching with Theory
15cm Single Paper
dB
V (m/s)
Predicted (m/s) Deviation (m/s) Deviation %
79.00
6.80
7.08
-0.28
4.14%
82.60
8.30
8.13
0.17
2.04%
87.40
9.30
9.78
-0.48
5.11%
89.00
10.70
10.39
0.31
2.86%
90.50
11.20
11.01
0.19
1.69%
AVG 3.17%
Table 1.Deviation of theoretical prediction from experimental results
Using the Paper Anemometer
• Set up the experimental device with a paper
strip and a decibel meter.
• Calibrate the device with air flows of different
known velocities.
• Calculate the ratio k from the velocity-decibel
relationship.
Using the Paper Anemometer
• Blow on the paper strip with an air flow of
unknown velocity and measure the sound
pressure level.
• Convert decibels to sound intensity. Using the
relationship v 6  I , the velocity of the air
flow may be obtained.