Full-annulus simulations of airfoil clocking in a compressor at off-design operating conditions

Axial compressors have inherently unsteady flow fields because of relative motion between rotor and stator airfoils. This relative motion leads to viscous and inviscid interactions between blade rows. As the number of stages increases in a turbomachine, the buildup of convected wakes can lead to progressively more complex wake/wake and wake/airfoil interactions. Variations in the relative circumferential positions of airfoils in adjacent rotating or cion-rotating blade rows can change these interactions, leading to different unsteady forcing functions on airfoils and different compressor efficiencies. In addition, as the Mach number increases the interaction between blade rows can be intensified due to potential effects. It has been shown, both experimentally and computationally, that airfoil clocking can be used to improve the efficiency and reduce the unsteadiness in multiple-stage axial turbomachines with equal blade counts. While previous investigations have provided an improved understanding of the physics associated with airfoil clocking, more research is needed to determine if airfoil clocking is viable for use in modern gas-turbine compressors. This paper presents the results of a combined experimental/computational research effort intended to study the physics of at design and off-design operating conditions in a high-speed axial compressor. Experiments and computational simulations of airfoil clocking have been performed for operating conditions corresponding to design flow, near stall and near choke. The experimental portion of the work represents the completion of a long-term study on the effects of airfoil clocking on the performance of a 1-1/2 stage subsonic compressor. To accurately model the experimental compressor, the numerical simulations model the full annulus of 34 IGV, 35 rotor and 34 stator airfoils. Time-averaged and unsteady data (including performance quantities) are presented.