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Aerodynamic noise generation in centrifugal turbomachinery

Abstract

The objective of this research was to identify which aspects of the fluid dynamics are associated with noise generation in centrifugal turbomachinery. Research emphasis was placed on the generation of noise at frequencies other than the blade passage tones. In order to avoid noise generated by the interaction of the discharged flow and stationary objects outside of the impeller, experiments are performed on a centrifugal impeller without diffuser and casing. With this discharge configuration, the radiated noise spectra are shown to be dominated by harmonically related broad humps at low frequency. These were proven to be generated by the interaction of a coherent unsteady flow structure rotating around the impeller discharge and the trailing edges of the impeller blades.

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Abbreviations

a :

Speed of sound

b :

Impeller blade width

C :

Length of the impeller blade along the surface

D :

Impeller diameter

f :

Frequency (Hz)

F :

Acoustic source spectral distribuition function

G :

Acoustic frequency response function

L :

Non-dimensional power spectral density

m :

Azimuthal mode number

p :

Pressure

P ref :

Reference acoustic pressure (20 μPa)

Q :

Volume flow rate

r :

Radius in cylindrical coordinates

R :

Impeller radius

U :

Phase averaged mean velocity in rotating coordinates

V :

Phase averaged mean velocity in laboratory coordinates

V tip :

Impeller tip speed (RΩ)

z :

Axial distance from the shroud

Z :

Number of impeller blades (7)

r :

Radial distance from the impeller

He :

Helmholtz number (fD/a)

St :

Strouhal number based on the impeller tip speed (πD/Z)(f/V tip )

ρ o :

Standard air density (1.21 kg/m3)

ϕ:

Flow coefficient (Q/πbDV tip )

ψ:

Head rise coefficient (Δp/V tip 2)

ω:

Angular rotational speed of the instability pattern (rad/sec)

Ω:

Angular rotational speed of the impeller (rad/sec)

p :

Pressure

r :

Radial

R :

Rotating coordinates

S :

Stationary coordinates

u :

Velocity in rotating coordinates

v :

Velocity in stationary coordinates

References

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Author information

Correspondence to Jong-Soo Choi.

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Choi, J. Aerodynamic noise generation in centrifugal turbomachinery. KSME Journal 8, 161 (1994). https://doi.org/10.1007/BF02953265

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Key words

  • Centrifugal Impeller
  • Centrifugal Turbomachinery
  • Aerodynamic Noise
  • Discharge Flow Instability
  • Trailing Edge Noise