Aeroelastic Impact Of A Circumferentially Varying Tip Gap

The tip leakage flow in axial compressors is a significant factor in engine performance and a subject of investigation over the last several decades. Many studies have already shown that the vortices generated by this tip leakage can have a negative impact on the surrounding flow field and overall performance, and lead to excitations as well. This study examines the effect of these vortices on aeroelasticity, specifically, the effect of a circumferentially varying tip gap; such as that produced by casing ovalization. For this paper, a single passage, structured grid, CFD model of a compressor\u27s mid-stage rotor-stator configuration was analyzed using StarCCM+\u27s harmonic balance solver. This was a frequency domain calculation, which provided significant time savings relative to the more conventional time accurate approach. The vibratory results from an Abaqus model were incorporated into the CFD in order to calculate the aerodynamic work. The calculation modeled a circumferentially varying tip gap representative of what is seen in a real engine, and results were compared to solutions from models with circumferentially constant gaps. Furthermore, test data from an industrial gas turbine was utilized in order to recreate realistic levels of tip gap variation, as well as to validate the mechanical modeLs vibratory results. The calculations showed that for the gap variation imposed, the work per cycle was increased by 59% relative to a case with constant gaps