Session: 14-02 Compressor Cavities 2

Paper Number: 126600

126600 - Mass and Heat Exchange in Rotating Compressor Cavities With Variable Cob Separation 

Next generation aeroengines will operate at ever-increasing pressure ratios with smaller cores, where the control of blade-tip clearances across the flight cycle is an emerging design challenge. Such clearances are affected by the thermal expansion of the compressor discs that hold the blades, where acute thermal stresses govern operating life. The cavities formed by co-rotating discs feature a heated shroud at high radius and cooler cobs at low radius. A three-dimensional, unsteady and unstable flow structure is induced by destabilising buoyancy forces. The radial distribution of disc temperature is driven by a conjugate heat transfer at Grashof numbers of order 10^13. Such flows are further influenced by the heat and mass exchange with an axial throughflow of cooling air at low radius, where interaction depends on the Rossby number and separation of the disc cobs.

This paper presents a model to predict the cavity-throughflow interaction, and disc and fluid-core temperatures. The physics-based methodology provides expedient, reduced-order solutions to the complex conjugate problem appropriate for practical engine thermo-mechanical design. The model is validated by new experimental measurements using the Bath Compressor Cavity Rig, where variable disc cob spacings were investigated over a range of engine-representative conditions. Unsteady pressure measurements collected in the frame of reference of the rotating discs reveal new insight into the fundamentally aperiodic nature of the flow structure.

Presenting Author: Tom Nicholas University of Bath

Presenting Author Biography: Tom is a third year PhD student in the Department of Mechanical Engineering at the University of Bath. Tom’s research is focused on the internal air systems of gas turbine engines, particularly the fluid dynamics and heat transfer associated with buoyancy-induced flow in compressors. He develops novel theoretical models, which require a good knowledge of fluid mechanics and heat transfer, and he writes the computational codes to solve the resulting equations.

Authors:

Tom Nicholas University of Bath
Mikolaj Pernak University of Bath
Gary Lock University of Bath
James Scobie University of Bath
Hui Tang University of Bath