1 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)

A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007

Vibration analysis and noise reduction of the swinging unit

2 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)

A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007

Noise components of ducted fans

• Flow source Trace noise Noise of the turbulent boundary layer Noise of the separated flow region

• Mechanical source Noise of the drive train Noise of the excited cover Noise of the PWM control

3 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)

A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007

Flow source noises

• Trace noise

• Noise of the turbulent boundary layer

0

0

drag

lifting

F

FS

4 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)

A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007

Flow source noises

•Noise of the separated boundary layer

Proper and improper constructions for the entrance region

(1) Separation bubble (1) Laminar sublayer(2) Turbulent boundary

layer

5 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)

A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007

Mechanical source noises

Finite element modal analysis

•DOF: 162168•N. of elements: 26824 •Solver: COSMOS

Mesh: Mode shape at 48.55 Hz:

6 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)

A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007

Mechanical source noises

Results

Number of natural frequencies in each 20 Hz range

7 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)

A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007

Measurement

• Four-channel-measurement 2 accelerometers microphone tachometer

8 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)

A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007

Measurement

Zero pitch

Max pitch direction 1

Max pitchdirection 2

9 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)

A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007

Waterfall diagrams

Microphone signal compared with finite element results

10 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)

A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007

Waterfall diagrams

Microphone signal scaled by rpm

11 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)

A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007

Waterfall diagrams

The 8 kHz PWM noise appearing in the signal of the 2nd accelerometer

12 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)

A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007

The 8 kHz PWM noise appearing in the signal of the microphone

13 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)

A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007

Conclusions

Reduction or elimination of noise components

• Flow source components Trace noise - Not significant Noise of the turbulent boundary layer - By choosing better airfoil Noise of the separated flow region - Proper contstruction of the

entrance region

• Mechanical source components Noise of the excited cover - By increasing stiffness, rarefying

natural frequencies Noise of the PWM control - By raising controller frequency

above human hearing limit

Estimated total possible noise reduction:dBALA 86