Theoretical Model of Buoyancy-Induced Heat Transfer in Closed Compressor Rotors

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

The cavities between the rotating compressor discs in aeroengines are open, and there is an axial throughflow of cooling air in the annular space between the centre of the discs and the central rotating compressor shaft. Buoyancy-induced flow occurs inside these open rotating cavities, with an exchange of heat and momentum between the axial throughflow and the air inside the cavity. However, even where there is no opening at the centre of the compressor discs – as is the case in some industrial gas turbines – buoyancy-induced flow can still occur inside the closed rotating cavities. The closed cavity also provides a limiting case for an open cavity when the axial clearance between the cobs – the bulbous hubs at the centre of compressor discs - is reduced to zero.
Bohn and his co-workers at the University of Aachen have studied three different closed-cavity geometries, and they have published experimental data for the case where the outer cylindrical surface is heated and the inner surface is cooled. In this paper, a buoyancy model is developed in which it is assumed that the heat transfer from the cylindrical surfaces is analogous to laminar free convection from horizontal plates, with the gravitational acceleration replaced by the centripetal acceleration. The resulting equations, which have been solved analytically, show how the Nusselt numbers depend on both the geometry of the cavity and its rotational speed. The theoretical solutions show that compressibility effects in the core attenuate the Nusselt numbers, and there is a critical Reynolds number at which the Nusselt number will be a maximum. For the three cavities tested, the predicted Nusselt numbers are in generally good agreement with the measured values of Bohn et al. over a large range of Raleigh numbers up to values approaching 1012. The fact that the flow remains laminar even at these high Rayleigh numbers is attributed to the Coriolis accelerations suppressing turbulence in the cavity, which is consistent with recently-published results for open rotating cavities.
LanguageEnglish
Title of host publicationASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition
Place of PublicationCharlotte, North Carolina, USA
PagesV05BT15A002
Number of pages9
VolumeVolume 5B: Heat Transfer
ISBN (Electronic)978-0-7918-5088-6
StatusPublished - 2017

Fingerprint

compressor rotors
buoyancy
heat transfer
cavities
compressors
Nusselt number
compressibility effects
air cooling
hubs
gas turbines
clearances
Rayleigh number
geometry
laminar flow
free convection

Cite this

Tang, H., & Owen, J. (2017). Theoretical Model of Buoyancy-Induced Heat Transfer in Closed Compressor Rotors. In ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition (Vol. Volume 5B: Heat Transfer, pp. V05BT15A002). [GT2017-63060] Charlotte, North Carolina, USA.

Theoretical Model of Buoyancy-Induced Heat Transfer in Closed Compressor Rotors. / Tang, Hui; Owen, John.

ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. Vol. Volume 5B: Heat Transfer Charlotte, North Carolina, USA, 2017. p. V05BT15A002 GT2017-63060.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Tang, H & Owen, J 2017, Theoretical Model of Buoyancy-Induced Heat Transfer in Closed Compressor Rotors. in ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. vol. Volume 5B: Heat Transfer, GT2017-63060, Charlotte, North Carolina, USA, pp. V05BT15A002.
Tang H, Owen J. Theoretical Model of Buoyancy-Induced Heat Transfer in Closed Compressor Rotors. In ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. Vol. Volume 5B: Heat Transfer. Charlotte, North Carolina, USA. 2017. p. V05BT15A002. GT2017-63060
Tang, Hui ; Owen, John. / Theoretical Model of Buoyancy-Induced Heat Transfer in Closed Compressor Rotors. ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. Vol. Volume 5B: Heat Transfer Charlotte, North Carolina, USA, 2017. pp. V05BT15A002
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