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.

The flow inside cavities between co-rotating compressor discs of aero-engines is driven by buoyancy, with Grashof numbers exceeding 1013. 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 change in compressor blade-tip clearance across the flight cycle depends on the expansion of the rotor, which in turn depends on the temperature and stress in the discs. The radial distribution of temperature is directly coupled to the buoyancy-driven flow and heat transfer in the rotating disc cavities. This paper describes a new test rig specifically designed to investigate this conjugate phenomenon. The rig test section includes four rotating discs enclosing three cavities. Two discs in the central cavity are instrumented with thermocouples to provide the radial distribution of temperature; the two outer cavities are thermally insulated to create appropriate boundary conditions for the heat transfer analysis. An axial throughflow of air is supplied between a stationary shaft and the bore of the discs. The temperature of the throughflow air is measured by thermocouples in rakes upstream and downstream of the central cavity. For a cold throughflow, the outer shroud of the central cavity is heated. Two independently-controlled radiant heaters allow differential shroud temperatures for the upstream and downstream discs, as found in aero-engine compressors. Alternatively, the throughflow can be heated above the shroud temperature to simulate the transient conditions during engine operation where stratified flow can occur inside the cavity. The rig is designed to operate in conditions where both convective and radiative heat transfer dominate; all internal surfaces of the cavity are painted matt black to allow the accurate calculation of the radiant heat transfer.

Abstract For the next generation of aero-engines, manufacturers are planning to increase the overall compressor pressure ratio from the existing values around 50:1 to values of 70:1. The requirement to control the tight clearances between the blade tips and the casing overall engine-operating conditions is a challenge for the engine designer attempting to minimize tip-clearances losses. Accurate prediction of the tip clearance requires an accurate prediction of the radial growth of the compressor rotor, which depends on the temperature distribution of the disk. The flow in the rotating cavities between adjacent disks is buoyancy-driven, which creates a conjugate heat transfer problem: the disk temperature depends on the radial distribution of the Nusselt number, which in turn depends on the radial distribution of disk temperature. This paper focuses on calculating the radial growth of a simplified compressor disk in isolation from the other components. Calculations were performed using steady one-dimensional (1D) theoretical and two-dimensional numerical computations (2D finite element analysis (FEA)) for overall pressure ratios (OPRs) of 50:1, 60:1, and 70:1. At each pressure ratio, calculations were conducted for five different temperature distributions; the distribution based on an experimentally validated buoyancy model was used as the datum case, and the results from this were compared with those from linear, quadratic, cubic, and quartic power laws. The results show that the assumed distribution of disk temperature has a significant effect on the calculated disk growth, whereas the pressure ratio has only a relatively small effect. Good agreement between the growth calculated by the 1D theoretical model and the FEA suggests that the 1D model should be useful for design purposes. Although the results were obtained for steady-state conditions, a method is outlined for calculating the growth under transient conditions.

For the next generation of aero-engines, manufacturers are planning to increase the overall compressor pressure ratio from existing values around 50:1 to values of 70:1. The requirement to control the tight clearances between the blade tips and the casing over all engine-operating conditions is a challenge for the engine designer attempting to minimise tip-clearances losses. Accurate prediction of the tip clearance requires an accurate prediction of the radial growth of the compressor rotor, which depends on the temperature distribution of the disc. The flow in the rotating cavities between adjacent discs is buoyancy-driven, which creates a conjugate heat transfer problem: the disc temperature depends on the radial distribution of Nusselt number, which in turn depends on the radial distribution of disc temperature. This paper focuses on calculating the radial growth of a simplified compressor disc in isolation from the other components. Calculations were performed using one-dimensional (1D) theoretical and two-dimensional finite-element computations (2D FEA) for overall pressure ratios (OPR) of 50:1, 60:1 and 70:1. At each pressure ratio, calculations were conducted for five different temperature distributions; the distribution based on an experimentally-validated buoyancy model was used as the datum case, and results from this were compared with those from linear, quadratic, cubic and quartic power laws. The results show that the assumed distribution of disc temperature has a significant effect on the calculated disc growth, whereas the pressure ratio has only a relatively small effect. The good agreement between the growth calculated by the 1D theoretical model and the FEA suggests that the 1D model should be useful for design purposes.