Toward Intra-Row Gap Optimization for One and Half Stage Transonic Compressor

Multistage effects on both aerodynamics and aeromechanics have been identified as significant. Thus, design optimizations for both aerodynamic performance and aeromechanical stability should be done in the unsteady multistage environment. The key issue preventing such a procedure to be carried out is the enormous computing time cost of multistage unsteady simulations. In this paper, a methodology based on the single-passage shape-correction method integrated with an interface disturbance truncation technique has been developed. The capability, efficiency, and accuracy of the developed methodology have been demonstrated for a one and a half stage quasi-three-dimensional transonic compressor with realistic blade counts. Furthermore, the interface disturbance truncation technique enables us to separate multirow interaction effects from the upstream and the downstream, which makes it possible to superimpose different rotor upstream gap effects and rotor downstream gap effects on the middle row rotor aerodynamic damping. In addition, a gap influence coefficient approach has been developed for investigation of all the possible gap spacing combinations of $M$ upstream stator-rotor gaps and $N$ downstream rotor-stator gaps. Then the number of cases that need to be computed has been reduced from $M×N$ to $M+N$⁠, which saved substantial computing time. The optimization analysis shows significant damping variation $(∼300%)$ within the chosen intrarow gap design space. The intrarow gap spacing could have either stabilizing or destabilizing effects so that the stabilizing axial spacing could be utilized to increase flutter-free margin in aeromechanical designs. The current approach also can be used for setting aeromechanical constraints for aerodynamic performance optimizations.