Spatial Decomposition of Aerodynamic Forcing and Interference Diagram: The Effects of Clocking on Aeromechanic Assessment

This paper describes an extensive numerical study aimed at the evaluation of the impact of rotor-rotor and stator-stator rel-ative position, better known as clocking, of two consecutive axial compressor stages on the unsteady pressure forcing for the aer-omechanic assessment of blade-rows. The two stages under con-siderations are derived from a 11-stage compressor. The analysis takes advantage of the spatial decomposition theory that is expected to improve the practical application of the interference diagram. The airfoil pressure perturbation is used to measure the unsteadiness content related to a specific engine order. The numerical analysis investigates both rotor and stator clocking since the two stage of interest may have the same rotor and stator airfoil count. First, the analysis focuses on the differences in the unsteady decomposed forcing at nominal speed. Also, results in-dicate no impact on the overall two stage efficiency. The same analysis is repeated at lower speed to determine if the clocking position with the minimum forcing holds approximately valid across the rotational speed range of the compressor. The com-parison of the two unsteady flow fields reveals that the clocking position that minimizes the unsteady lift changes with the rota-tional speed. Additional computations are carried out by chang-ing the rotor count to investigate the effect on unsteady lift. Fi-nally, the effect of stator clocking on rotor unsteady lift is also investigated in a set of additional runs and the results are dis-cussed.