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

[+] Author and Article Information
Hui Tang

Department of Mechanical Engineering, University of Bath, Bath, BA2 7AY, United Kingdom

J. Michael Owen

Department of Mechanical Engineering, University of Bath, Bath, BA2 7AY, United Kingdom

1Corresponding author.

ASME doi:10.1115/1.4037926 History: Received July 11, 2017; Revised July 24, 2017


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. 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 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 10^12.

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