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Vibration analysis and noise reduction of the swinging unit

Vibration analysis and noise reduction of the swinging unit. 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.

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Vibration analysis and noise reduction of the swinging unit

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  1. Vibration analysis and noise reduction of the swinging unit

  2. 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. Flow source noises • Trace noise • Noise of the turbulent boundary layer

  4. Flow source noises • Noise of the separated boundary layer • Proper and improper constructions for the entrance region • Laminar sublayer • Turbulent boundary layer (1) Separation bubble

  5. Mechanical source noises Finite element modal analysis • DOF: 162168 • N. of elements: 26824 • Solver: COSMOS Mesh: Mode shape at 48.55 Hz:

  6. Mechanical source noises Results Number of natural frequencies in each 20 Hz range

  7. Measurement • Four-channel-measurement • 2 accelerometers • microphone • tachometer

  8. Measurement Zero pitch Max pitch direction 1 Max pitch direction 2

  9. Waterfall diagrams Microphone signal compared with finite element results

  10. Waterfall diagrams Microphone signal scaled by rpm

  11. Waterfall diagrams The 8 kHz PWM noise appearing in the signal of the 2nd accelerometer

  12. The 8 kHz PWM noise appearingin the signal of the microphone

  13. Conclusions • 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 Reduction or elimination of noise components Estimated total possible noise reduction:

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