Influence of a tip blowing casing treatment on the stator flow

In modern turbo machines, the stage loading in compressors is significantly increased to meet the power demand with enhanced efficiency. Casing treatments have proven to be effective in preventing stability issues that occur due to the high stage loading. Most numerical casing treatment studies cover only the rotor and neglect the stage behavior. However, the stage behavior is obviously impacted and the stator has to be redesigned if the rotor is treated. The present study investigates a 1.5 stage transonic and tip critical compressor. The stage was designed without a casing treatment. However, using a casing treatment now widely extend the operating range of the rotor, thus increasing its overall total pressure ratio. Therefore, the stator has also to cover a broader operating range. As the stator was not designed for this degree of throttling, surge is now triggered by the stator. In order to redesign the stator, the authors investigate the baseline stator to identify the reasons for failure and draw conclusions regarding the influence of the tip blowing casing treatment on the stator. The numerical investigation of the combined rotor and stator shows, on the one hand, the influence of the connecting interface on the compressor characteristic and the flow field. A model with a mixing plane interface is compared to a setup with a sliding plane interface. On the other hand, while using the circumferentially discrete interface, the influence of the tip blowing on the downstream stator is analyzed in depth.