The paper discusses origins of fan noise that pertain particularly to vehicles having confined power units. It is known that a fan running in a smooth flow and clean environment produces virtually no discrete components and A moderate level of random or broad bank noise. The environmental conditions in which many fans have to operate in practice are far from ideal and they can give rise to flow conditions through the fan which produce high levels of both discrete and random components. It is necessary to study the detailed flow paterns in units subjected to representative changes to determine methods of reducing the effects. The level of random noise depends essentially on the loading on the individual blades and, in particular, on the lift fluctuations represented by the turbulent pressure fluctuations in the boundary layers on the blades. If the pressure fluctuations are correlated on the blade, discrete tones may appear on the spectra. These features are discussed from a theoretical standpoint with associated experimental data. Tip clearance between the Blade and shaft vibration generate regular variations in the tip clearance and hence in the tip loading and the noise level. The paper presents theoretical calculations of this effect and early results from an experimental rig specifically designed to investigate this problem. Finally, our recent experimental results show that the noise from a blade in a smooth flow is much lower than predicted by existing formulae, notably sharland. With this in mind it is necessary to recalculate the penalty of having highly turbulent and badly distorted flow impinging on the fan from the radiator system.(a). For /TRRL/ associated experimental data.

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 217-235

Subject/Index Terms

Filing Info

  • Accession Number: 00137801
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • ISBN: 0853346429
  • Report/Paper Numbers: Proceeding
  • Files: ITRD, TRIS
  • Created Date: Apr 27 1977 12:00AM