Computational fluid dynamics simulations of blade damage effect on the performance of a transonic axial compressor near stall

Gas turbine axial compressor blades may encounter damage during service for various reasons such as damage by debris from casing or foreign objects impacting the blades, typically near the rotor's tip. This may lead to deterioration of performance and reduction in the surge margin. The damage breaks the cyclic symmetry of the rotor assembly; thus, computational fluid dynamics simulations have to be performed using full annulus compressor assembly. Moreover, downstream boundary conditions are unknown during rotating stall or surge, and simulations become difficult. This paper presents unsteady computational fluid dynamics analyses of compressor performance with tip curl damage. Computations were performed near the stall boundary. The primary objectives are to understand the effect of the damage on the flow behaviour and compressor stability. Computations for the undamaged rotor assembly were also performed as a reference case. A transonic axial compressor rotor was used for the time-accurate numerical unsteady flow simulations, with a variable area nozzle downstream simulating an experimental throttle. Computations were performed at 60% of the rotor design speed. Two different degrees of damage for one blade and multiple damaged blades were investigated. Rotating stall characteristics differ including the number of stall cells, propagation speed and rotating stall cell characteristics. Contrary to expectations, damaged blades with typical degrees of damage do not show noticeable effects on the global compressor performance near stall.