Validation of Steady and Unsteady CFD Strategies in the Design of Axial Compressors for Gas Turbine Engines

Steady and unsteady CFD predictions of a state-of-the-art 11-stage axial compressor performances are compared with measurements and scrutinized to determine their ability to assist in the design phase. Unsteady calculations are capable of reproducing the measured stage loads and spanwise stagnation temperature and pressure profiles with good accuracy, while front-to-back stage loads predicted by the steady calculations deviate from measurements and result in an unrealistic early stall. Numerical experiments in design and off-design conditions suggest that unsteady effects change stage loads mostly through a deformation of the spanwise flow profiles, the primary driver of the compressor operability limits. Hence, single stage steady calculations, generally used in design iterations, are demonstrated to reproduce the single stage performance extracted from full multistage unsteady calculation by simply enforcing the time averaged inlet and exit spanwise profiles extracted from the multistage run. The proposed approach may reduce the computational effort in design loops by reducing the number of unsteady runs in favor of single stage steady runs with time averaged boundary conditions.