Measurement and Analysis of Buoyancy-Induced Heat Transfer in Aero-Engine Compressor Rotors

Abstract

The flow inside cavities between co-rotating compressor discs of aero-engines is driven by buoyancy, with Grashof numbers exceeding 10 13 . This phenomenon creates a conjugate problem: the Nusselt numbers depend on the radial temperature distribution of the discs, and the disc temperatures depend on the Nusselt numbers. Furthermore, Coriolis forces in the rotating fluid generate cyclonic and anti-cyclonic circulations inside the cavity. Such flows are three-dimensional, unsteady and unstable, and it is a challenge to compute and measure the heat transfer from the discs to the axial throughflow in the compressor. In this paper, Nusselt numbers are experimentally determined from measurements of steady-state temperatures on the surfaces of both discs in a rotating cavity of the Bath Compressor-Cavity Rig. The data are collected over a range of engine-representative parameters and are the first results from a new experimental facility specifically designed to investigate buoyancy-induced flow. The radial distributions of disc temperature were collected under carefully-controlled thermal boundary conditions appropriate for analysis using a Bayesian model combined with the equations for a circular fin. The Owen-Tang buoyancy model has been used to compare predicted radial distributions of disc temperatures and Nusselt numbers with some of the experimentally determined values, taking account of radiation between the interior surfaces of the cavity.The experiments show that the average Nusselt numbers on the disc increase as the buoyancy forces increase. At high rotational speeds the temperature rise in the core, created by compressibility effects in the air, attenuates the heat transfer and there is a critical rotational Reynolds number for which the Nusselt number is a maximum. In the cavity, there is an inner region dominated by forced convection and an outer region dominated by buoyancy-induced flow. The inner region is a mixing region, in which entrained cold throughflow encounters hot flow from the Ekman layers on the discs. Consequently, the Nusselt numbers on the downstream disc in the inner region tend to be higher than those on the upstream disc.

Large Eddy Simulation Investigation of Low Rossby Number Buoyant Flow in Rotating Cavities

“…The geometry used here models a test rig at the University of Bath, as reported recently by Jackson et al [5]. A view of the rig working section is shown in Fig.…”

“…The width and radius ratios of the cavity are 𝑠/𝑏 = 0.17 and 𝑎/𝑏 = 0.29. For further information of the test rig and instrumentations, readers are advised to refer to Jackson et al [5] and Luberti et al [10]. In the present study, the single cavity model is based on the Bath experimental rig.…”

“…Previous research in this area has been discussed in a number of recent papers, for example Refs. [1][2][3][4][5][6], and so only the most recent and directly relevant studies are mentioned here. The complex nature of the rotating cavity flow has long been recognised.…”

“…Saini and Sandberg [6] give results for cases with Rossby number 𝑅𝑜 = 4.5 and rotational Reynolds number 𝑅𝑒 𝛺 = 7.8 × 10 4 using wallresolved LES. Gao and Chew [1] give results for cases with 𝑅𝑜 = 0.4 to 0.8 and 𝑅𝑒 𝛺 = 3.2 × 10 5 to 2.2 × 10 6 using wall-modelled LES (WMLES), and include comparison with recent experimental data from the University of Bath [5,9,10], respectively. Their interpretation of the flow and heat transfer mechanisms is summarised in Fig.…”

Design and Testing of a Rig to Investigate Buoyancy-Induced Heat Transfer in Aero-Engine Compressor Rotors

“…Careful consideration was also given to the analysis of the data and to the estimation of the uncertainties in the calculated Nusselt numbers. As this is an inverse problem, in which small uncertainties in the temperature measurement lead to very large uncertainties in the calculated heat fluxes, a Bayesian statistical model was used to calculate the fluxes; details of this are given in the paper by Jackson et al [15]. As buoyancy -induced flow is a conjugate problem, in which the conduction in the discs is coupled to convection in the air inside the cavity, the Bayesian model was used in conjunction with a one-dimensional circular fin equation for the conduction solution.…”