Distortion Transfer in Multi-Stage Compressor and Modeling of Spool-Coupling Problem With Circumferentially Distorted Inflow

Abstract Among various types of total pressure distortion, circumferential distortion is well known to reduce the operability range of the aero engine. The effect of the circumferential total pressure distortion on single-stage fans have been studied by various researchers. There are, however, few studies about the effect of the circumferential total pressure distortion on multistage compressors. It is also known that in the case of turbojet engines or low bypass ratio turbofan engines, not only the LPC (fan) but also the HPC is influenced by the circumferential distortion. This is called spool coupling effect. However, no method has been fully established to assess the effect of the circumferential distortion on each component and eventually on the whole engine. In the first part of the present study, the flow field of a multistage research compressor, the front six stages of the Energy Efficient Engine, under circumferentially distorted inflow is analyzed using the Body Force Method, whose coefficients are tuned using the steady RANS solution of the compressor with clean inlet flow. The computed results show that, while the rear stage operates much like in the way described by the parallel compressor model, the front stage experiences circumferential aero loading fluctuations due to the static pressure field formed at the boundaries of the distortion. Consistency of the results is qualitatively confirmed based on comparisons with theory. In the second part of the study, a new engine performance model including spool coupling effect is proposed. It is a so-called “Parallel Engine” model, in which all the components are divided into distorted and undistorted sectors. The spool coupling effect is represented by a single parameter, namely the normalized axial gap between LPC and HPC. Change in the performance of a notional turbojet engine with circumferential distortion due to the spool coupling effect is presented. Outlook to combine the two methods is briefly summarized at the end.