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

Metal Wire

Wind Blower

Voltage Regulator

Experimental Setup

4 cm 20 cm3.3 cm

Spaced Double 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

Chart 1.Finding the optimum paper length for experiment

Optimal Range

Experiment: Intensity

Chart 3.The relationship between flow velocity and decibels measured when using different lengths of paper

Experiment: Intensity

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 to fit our experimental data

6v k I

Matching with Theory

Matching with Theory

• Experimental results matches well with theory• Deviations seen more often at lower wind velocities

Matching with Theory

Table 1.Deviation of theoretical prediction from experimental results

15cm Single PaperdB 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%

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 , the velocity of the air flow may be obtained.

6v I