Conjugate Modelling of a Closed Co-Rotating Compressor Cavity

Robust methods to predict heat transfer are vital to accurately control the blade-tip clearance in compressors and the radial growth of the discs to which these blades are attached. Fundamentally, the flow in the cavity between the co-rotating discs is a conjugate problem: the temperature gradient across this cavity drives large-scale buoyant structures in the core that rotate asynchronously to the discs, which in turn governs the heat transfer and temperature distributions in the discs. The practical engine designer requires expedient computational methods and low-order modelling. A conjugate heat transfer methodology that can be used as a predictive tool is introduced here. Most simulations for rotating cavities only consider the fluid domain in isolation and typically require known disc temperature distributions as the boundary condition for the solution.

This paper presents a novel coupling strategy for the conjugate problem, where unsteady Reynolds Averaged Navier-Stokes (URANS) simulations for the fluid are combined with a series of steady simulations for the solid domain in an iterative approach. This strategy overcomes the limitations due to the difference in thermal inertia between fluid and solid; the method retains the unsteady flow features but allows a prediction of the disc temperature distributions, rather than using them as a boundary condition. This approach has been validated on the fundamental flow configuration of a closed co-rotating cavity. Metal temperatures and heat transfer correlations predicted by the simulation are compared to those measured experimentally for a range of engine-relevant conditions.