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

Abstract

An investigation into the behavior of two transonic compressor rotors operating at nearstall conditions while ingesting hotsteam 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 divided into three broad areas: experimental, theoretical and numerical. The first area, experimental, used the Naval Postgraduate School's transonic compressor rig. The rig was modified to introduce hot steam into the inlet flow during testing. Two rotoronly tests were completed; one with an unswept rotor and the other with a forward swept rotor. The experimental program yielded two sets of results. The first recorded data on the operational behavior of a transonic compressor ingesting a superheated steam and air mixture, notably the quantification of the stall margin (SM) reduction. The second data set captured transient measurements of the inlet flow gas properties. The transient inlet data were then used in the second research area; a theoretical analysis based on a thermodynamic model of the inlet flow. Prior to this investigation, little information was available for higher temperature steam–air mixtures of this type. The analysis used certain simplifying assumptions to perform a fundamental of the inflow which yielded the inlet flow transient changes of specific heat capacities, gas constants, and, therefore, sonic velocities. Using these transient inlet properties, the third area of the investigation was performed, developing a numerical model. A fully transient simulation over the time period of an ingestion event would not be practical due to the large computational requirements needed. A quasitransient method with large intermediate time steps was developed. The method is presented and was found to be reasonable at predicting the stallmargin reduction when compared to the available experimental results. These results would have potential use in design applications and for evaluating existing compressor steam ingestion tolerance.