Lattice-Boltzmann modeling of centrifugal buoyancy-induced flows in rotating compressor cavities

Abstract

Turbofan compressor cooling circuits exhibit inherent unsteadiness within their cavities due to the interplay of forced and natural convection phenomena. This dynamic is fueled by axial cooling throughflow, centrifugal forces, and large temperature gradients. This paper introduces an extended compressible lattice-Boltzmann approach tailored for accurately modeling centrifugal buoyancy-driven flows in such cavities. The approach integrates a local rotating reference frame model into a hybrid thermal lattice Boltzmann method, facilitating the simulation of rotating flows of perfect gases. Moreover, a new mass-conserving boundary treatment, based on the reconstruction of distribution functions, enhances precision in predicting rotor disk heat transfer. Finally, an adapted direct-coupling mesh-refinement strategy, accounting for source terms at grid transitions, enables efficient high buoyancy flow simulations. The proposed approach effectively recovers flow and heat transfer mechanisms on sealed and open rotating compressor cavity rigs, spanning a large range of Rayleigh numbers (up to 109). Through an analysis of the compressibility effects, adjustments to the adiabatic exponent and Eckert number allow for a significant boost in computational speed without undermining the reliability of the flow and heat transfer dynamics, aligning well with established theoretical models and numerical studies. With computational efficiency that outperforms conventional compressible finite volume solvers, the proposed approach stands as a promising method for industrial-scale modeling of turbomachinery cooling circuits.