Investigation and Prediction of Steam-Induced Stall-Margin Reduction in Two Transonic Rotor Fans

Abstract

A comprehensive investigation into the behavior of two transonic compressor rotors operating at near-stall conditions while ingesting hot-steam was undertaken. This type of inlet flow was similar to that experienced by naval aircraft during steam catapult launches and has had the potential to adversely affect engine performance. The research was undertaken in three broad areas. The first phase of the investigation was experimental. The Naval Postgraduate School’s, transonic compressor rig was modified to include the capability of adding hot steam to the rig inlet flow. Two rotor-only tests, one with an unswept rotor and the other with a forward swept rotor were completed. The experimental program yielded two sets of results. The first was data on the operational behavior of a transonic compressor ingesting a super-heated steam and air mixture, notably the quantification of their stall margin reduction. The second was transient data of the inlet flow which was used in the next phase of the investigation. This second phase was a theoretical analysis based on a thermodynamic model of the inlet flow. It was found that little information was available for higher temperature steam-air mixtures of this type. The analysis used certain simplifying assumptions to perform a fundamental thermodynamic analysis of the inflow. This allowed insights to be gained into the inlet flow properties. The third part of the investigation was numerical. A fully transient simulation over the time period of interest would not be practical due to the large computational requirements that would be needed. A quasi-transient method with large intermediate time-steps was developed. It was found to be reasonable at predicting the stall-margin reduction when compared to the available experimental results while being computationally inexpensive. This would have potential use in design applications and for evaluating existing compressor steam ingestion tolerance.